JSON-RPC
JSONRPCErrorResponse
JSONRPCMessage
Refers to any valid JSON-RPC object that can be decoded off the wire, or encoded to be sent.
JSONRPCNotification
A notification which does not expect a response.
JSONRPCRequest
id: RequestId;
jsonrpc: “2.0”;
method: string;
params?: { [key: string]: any };
}
A request that expects a response.
JSONRPCResultResponse
A successful (non-error) response to a request.
Common Types
Annotations
Optional annotations for the client. The client can use annotations to inform how objects are used or displayed
Describes who the intended audience of this object or data is.
It can include multiple entries to indicate content useful for multiple audiences (e.g., [“user”, “assistant”]).
The moment the resource was last modified, as an ISO 8601 formatted string.
Should be an ISO 8601 formatted string (e.g., “2025-01-12T15:00:58Z”).
Examples: last activity timestamp in an open file, timestamp when the resource was attached, etc.
Describes how important this data is for operating the server.
A value of 1 means “most important,” and indicates that the data is effectively required, while 0 means “least important,” and indicates that the data is entirely optional.
Cursor
An opaque token used to represent a cursor for pagination.
EmptyResult
A response that indicates success but carries no data.
Error
The error type that occurred.
Additional information about the error. The value of this member is defined by the sender (e.g. detailed error information, nested errors etc.).
A short description of the error. The message SHOULD be limited to a concise single sentence.
Icon
An optionally-sized icon that can be displayed in a user interface.
Optional MIME type override if the source MIME type is missing or generic.
For example: “image/png”, “image/jpeg”, or “image/svg+xml”.
Optional array of strings that specify sizes at which the icon can be used.
Each string should be in WxH format (e.g., “48x48”, “96x96”) or “any” for scalable formats like SVG.
If not provided, the client should assume that the icon can be used at any size.
A standard URI pointing to an icon resource. May be an HTTP/HTTPS URL or a data: URI with Base64-encoded image data.
Consumers SHOULD takes steps to ensure URLs serving icons are from the same domain as the client/server or a trusted domain.
Consumers SHOULD take appropriate precautions when consuming SVGs as they can contain executable JavaScript.
Optional specifier for the theme this icon is designed for. light indicates
the icon is designed to be used with a light background, and dark indicates
the icon is designed to be used with a dark background.
If not provided, the client should assume the icon can be used with any theme.
LoggingLevel
| “debug”
| “info”
| “notice”
| “warning”
| “error”
| “critical”
| “alert”
| “emergency”
The severity of a log message.
These map to syslog message severities, as specified in RFC-5424: https://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1
ProgressToken
A progress token, used to associate progress notifications with the original request.
RequestId
A uniquely identifying ID for a request in JSON-RPC.
Result
See General fields: _meta for notes on _meta usage.
Role
The sender or recipient of messages and data in a conversation.
Content
AudioContent
_meta?: { [key: string]: unknown };
annotations?: Annotations;
data: string;
mimeType: string;
type: “audio”;
}
Audio provided to or from an LLM.
See General fields: _meta for notes on _meta usage.
Optional annotations for the client.
The base64-encoded audio data.
The MIME type of the audio. Different providers may support different audio types.
BlobResourceContents
_meta?: { [key: string]: unknown };
blob: string;
mimeType?: string;
uri: string;
}
See General fields: _meta for notes on _meta usage.
A base64-encoded string representing the binary data of the item.
The MIME type of this resource, if known.
The URI of this resource.
ContentBlock
EmbeddedResource
_meta?: { [key: string]: unknown };
annotations?: Annotations;
resource: TextResourceContents | BlobResourceContents;
type: “resource”;
}
The contents of a resource, embedded into a prompt or tool call result.
It is up to the client how best to render embedded resources for the benefit of the LLM and/or the user.
See General fields: _meta for notes on _meta usage.
Optional annotations for the client.
ImageContent
_meta?: { [key: string]: unknown };
annotations?: Annotations;
data: string;
mimeType: string;
type: “image”;
}
An image provided to or from an LLM.
See General fields: _meta for notes on _meta usage.
Optional annotations for the client.
The base64-encoded image data.
The MIME type of the image. Different providers may support different image types.
ResourceLink
_meta?: { [key: string]: unknown };
annotations?: Annotations;
description?: string;
icons?: Icon[];
mimeType?: string;
name: string;
size?: number;
title?: string;
type: “resource_link”;
uri: string;
}
A resource that the server is capable of reading, included in a prompt or tool call result.
Note: resource links returned by tools are not guaranteed to appear in the results of resources/list requests.
See General fields: _meta for notes on _meta usage.
Optional annotations for the client.
A description of what this resource represents.
This can be used by clients to improve the LLM’s understanding of available resources. It can be thought of like a “hint” to the model.
Optional set of sized icons that the client can display in a user interface.
Clients that support rendering icons MUST support at least the following MIME types:
image/png- PNG images (safe, universal compatibility)image/jpeg(andimage/jpg) - JPEG images (safe, universal compatibility)
Clients that support rendering icons SHOULD also support:
image/svg+xml- SVG images (scalable but requires security precautions)image/webp- WebP images (modern, efficient format)
The MIME type of this resource, if known.
Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn’t present).
The size of the raw resource content, in bytes (i.e., before base64 encoding or any tokenization), if known.
This can be used by Hosts to display file sizes and estimate context window usage.
Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.
If not provided, the name should be used for display (except for Tool,
where annotations.title should be given precedence over using name,
if present).
The URI of this resource.
TextContent
_meta?: { [key: string]: unknown };
annotations?: Annotations;
text: string;
type: “text”;
}
Text provided to or from an LLM.
See General fields: _meta for notes on _meta usage.
Optional annotations for the client.
The text content of the message.
TextResourceContents
_meta?: { [key: string]: unknown };
mimeType?: string;
text: string;
uri: string;
}
See General fields: _meta for notes on _meta usage.
The MIME type of this resource, if known.
The text of the item. This must only be set if the item can actually be represented as text (not binary data).
The URI of this resource.
completion/complete
CompleteRequest
id: RequestId;
jsonrpc: “2.0”;
method: “completion/complete”;
params: CompleteRequestParams;
}
A request from the client to the server, to ask for completion options.
CompleteRequestParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
argument: { name: string; value: string };
context?: { arguments?: { [key: string]: string } };
ref: PromptReference | ResourceTemplateReference;
}
Parameters for a completion/complete request.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
The argument’s information
- name: string
The name of the argument
- value: string
The value of the argument to use for completion matching.
Additional, optional context for completions
Optionalarguments?: { [key: string]: string }Previously-resolved variables in a URI template or prompt.
CompleteResult
_meta?: { [key: string]: unknown };
completion: { hasMore?: boolean; total?: number; values: string[] };
[key: string]: unknown;
}
The server’s response to a completion/complete request
See General fields: _meta for notes on _meta usage.
OptionalhasMore?: booleanIndicates whether there are additional completion options beyond those provided in the current response, even if the exact total is unknown.
Optionaltotal?: numberThe total number of completion options available. This can exceed the number of values actually sent in the response.
- values: string[]
An array of completion values. Must not exceed 100 items.
PromptReference
Identifies a prompt.
Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn’t present).
Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.
If not provided, the name should be used for display (except for Tool,
where annotations.title should be given precedence over using name,
if present).
ResourceTemplateReference
A reference to a resource or resource template definition.
The URI or URI template of the resource.
elicitation/create
ElicitRequest
id: RequestId;
jsonrpc: “2.0”;
method: “elicitation/create”;
params: ElicitRequestParams;
}
A request from the server to elicit additional information from the user via the client.
ElicitRequestParams
The parameters for a request to elicit additional information from the user via the client.
ElicitResult
_meta?: { [key: string]: unknown };
action: “accept” | “decline” | “cancel”;
content?: { [key: string]: string | number | boolean | string[] };
[key: string]: unknown;
}
The client’s response to an elicitation request.
See General fields: _meta for notes on _meta usage.
The user action in response to the elicitation.
- “accept”: User submitted the form/confirmed the action
- “decline”: User explicitly decline the action
- “cancel”: User dismissed without making an explicit choice
The submitted form data, only present when action is “accept” and mode was “form”. Contains values matching the requested schema. Omitted for out-of-band mode responses.
BooleanSchema
default?: boolean;
description?: string;
title?: string;
type: “boolean”;
}
ElicitRequestFormParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
message: string;
mode?: “form”;
requestedSchema: {
$schema?: string;
properties: { [key: string]: PrimitiveSchemaDefinition };
required?: string[];
type: “object”;
};
task?: TaskMetadata;
}
The parameters for a request to elicit non-sensitive information from the user via a form in the client.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
The message to present to the user describing what information is being requested.
The elicitation mode.
$schema?: string;
properties: { [key: string]: PrimitiveSchemaDefinition };
required?: string[];
type: “object”;
}
A restricted subset of JSON Schema. Only top-level properties are allowed, without nesting.
If specified, the caller is requesting task-augmented execution for this request. The request will return a CreateTaskResult immediately, and the actual result can be retrieved later via tasks/result.
Task augmentation is subject to capability negotiation - receivers MUST declare support for task augmentation of specific request types in their capabilities.
ElicitRequestURLParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
elicitationId: string;
message: string;
mode: “url”;
task?: TaskMetadata;
url: string;
}
The parameters for a request to elicit information from the user via a URL in the client.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
The ID of the elicitation, which must be unique within the context of the server. The client MUST treat this ID as an opaque value.
The message to present to the user explaining why the interaction is needed.
The elicitation mode.
If specified, the caller is requesting task-augmented execution for this request. The request will return a CreateTaskResult immediately, and the actual result can be retrieved later via tasks/result.
Task augmentation is subject to capability negotiation - receivers MUST declare support for task augmentation of specific request types in their capabilities.
The URL that the user should navigate to.
EnumSchema
LegacyTitledEnumSchema
default?: string;
description?: string;
enum: string[];
enumNames?: string[];
title?: string;
type: “string”;
}
Use TitledSingleSelectEnumSchema instead. This interface will be removed in a future version.
(Legacy) Display names for enum values. Non-standard according to JSON schema 2020-12.
MultiSelectEnumSchema
NumberSchema
default?: number;
description?: string;
maximum?: number;
minimum?: number;
title?: string;
type: “number” | “integer”;
}
PrimitiveSchemaDefinition
Restricted schema definitions that only allow primitive types without nested objects or arrays.
SingleSelectEnumSchema
StringSchema
default?: string;
description?: string;
format?: “uri” | “email” | “date” | “date-time”;
maxLength?: number;
minLength?: number;
title?: string;
type: “string”;
}
TitledMultiSelectEnumSchema
default?: string[];
description?: string;
items: { anyOf: { const: string; title: string }[] };
maxItems?: number;
minItems?: number;
title?: string;
type: “array”;
}
Schema for multiple-selection enumeration with display titles for each option.
Optional default value.
Optional description for the enum field.
Schema for array items with enum options and display labels.
- anyOf: { const: string; title: string }[]
Array of enum options with values and display labels.
Maximum number of items to select.
Minimum number of items to select.
Optional title for the enum field.
TitledSingleSelectEnumSchema
default?: string;
description?: string;
oneOf: { const: string; title: string }[];
title?: string;
type: “string”;
}
Schema for single-selection enumeration with display titles for each option.
Optional default value.
Optional description for the enum field.
Array of enum options with values and display labels.
- const: string
The enum value.
- title: string
Display label for this option.
Optional title for the enum field.
UntitledMultiSelectEnumSchema
default?: string[];
description?: string;
items: { enum: string[]; type: “string” };
maxItems?: number;
minItems?: number;
title?: string;
type: “array”;
}
Schema for multiple-selection enumeration without display titles for options.
Optional default value.
Optional description for the enum field.
Schema for the array items.
- enum: string[]
Array of enum values to choose from.
- type: “string”
Maximum number of items to select.
Minimum number of items to select.
Optional title for the enum field.
UntitledSingleSelectEnumSchema
default?: string;
description?: string;
enum: string[];
title?: string;
type: “string”;
}
Schema for single-selection enumeration without display titles for options.
Optional default value.
Optional description for the enum field.
Array of enum values to choose from.
Optional title for the enum field.
initialize
InitializeRequest
id: RequestId;
jsonrpc: “2.0”;
method: “initialize”;
params: InitializeRequestParams;
}
This request is sent from the client to the server when it first connects, asking it to begin initialization.
InitializeRequestParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
capabilities: ClientCapabilities;
clientInfo: Implementation;
protocolVersion: string;
}
Parameters for an initialize request.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
The latest version of the Model Context Protocol that the client supports. The client MAY decide to support older versions as well.
InitializeResult
_meta?: { [key: string]: unknown };
capabilities: ServerCapabilities;
instructions?: string;
protocolVersion: string;
serverInfo: Implementation;
[key: string]: unknown;
}
After receiving an initialize request from the client, the server sends this response.
See General fields: _meta for notes on _meta usage.
Instructions describing how to use the server and its features.
This can be used by clients to improve the LLM’s understanding of available tools, resources, etc. It can be thought of like a “hint” to the model. For example, this information MAY be added to the system prompt.
The version of the Model Context Protocol that the server wants to use. This may not match the version that the client requested. If the client cannot support this version, it MUST disconnect.
ClientCapabilities
elicitation?: { form?: object; url?: object };
experimental?: { [key: string]: object };
roots?: { listChanged?: boolean };
sampling?: { context?: object; tools?: object };
tasks?: {
cancel?: object;
list?: object;
requests?: {
elicitation?: { create?: object };
sampling?: { createMessage?: object };
};
};
}
Capabilities a client may support. Known capabilities are defined here, in this schema, but this is not a closed set: any client can define its own, additional capabilities.
Present if the client supports elicitation from the server.
Experimental, non-standard capabilities that the client supports.
Present if the client supports listing roots.
OptionallistChanged?: booleanWhether the client supports notifications for changes to the roots list.
Present if the client supports sampling from an LLM.
Optionalcontext?: objectWhether the client supports context inclusion via includeContext parameter. If not declared, servers SHOULD only use
includeContext: “none”(or omit it).Optionaltools?: objectWhether the client supports tool use via tools and toolChoice parameters.
cancel?: object;
list?: object;
requests?: {
elicitation?: { create?: object };
sampling?: { createMessage?: object };
};
}
Present if the client supports task-augmented requests.
Optionalcancel?: objectWhether this client supports tasks/cancel.
Optionallist?: objectWhether this client supports tasks/list.
Optionalrequests?: { elicitation?: { create?: object }; sampling?: { createMessage?: object } }Specifies which request types can be augmented with tasks.
Optionalelicitation?: { create?: object }Task support for elicitation-related requests.
Optionalcreate?: objectWhether the client supports task-augmented elicitation/create requests.
Optionalsampling?: { createMessage?: object }Task support for sampling-related requests.
OptionalcreateMessage?: objectWhether the client supports task-augmented sampling/createMessage requests.
Implementation
description?: string;
icons?: Icon[];
name: string;
title?: string;
version: string;
websiteUrl?: string;
}
Describes the MCP implementation.
An optional human-readable description of what this implementation does.
This can be used by clients or servers to provide context about their purpose and capabilities. For example, a server might describe the types of resources or tools it provides, while a client might describe its intended use case.
Optional set of sized icons that the client can display in a user interface.
Clients that support rendering icons MUST support at least the following MIME types:
image/png- PNG images (safe, universal compatibility)image/jpeg(andimage/jpg) - JPEG images (safe, universal compatibility)
Clients that support rendering icons SHOULD also support:
image/svg+xml- SVG images (scalable but requires security precautions)image/webp- WebP images (modern, efficient format)
Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn’t present).
Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.
If not provided, the name should be used for display (except for Tool,
where annotations.title should be given precedence over using name,
if present).
An optional URL of the website for this implementation.
ServerCapabilities
completions?: object;
experimental?: { [key: string]: object };
logging?: object;
prompts?: { listChanged?: boolean };
resources?: { listChanged?: boolean; subscribe?: boolean };
tasks?: {
cancel?: object;
list?: object;
requests?: { tools?: { call?: object } };
};
tools?: { listChanged?: boolean };
}
Capabilities that a server may support. Known capabilities are defined here, in this schema, but this is not a closed set: any server can define its own, additional capabilities.
Present if the server supports argument autocompletion suggestions.
Experimental, non-standard capabilities that the server supports.
Present if the server supports sending log messages to the client.
Present if the server offers any prompt templates.
OptionallistChanged?: booleanWhether this server supports notifications for changes to the prompt list.
Present if the server offers any resources to read.
OptionallistChanged?: booleanWhether this server supports notifications for changes to the resource list.
Optionalsubscribe?: booleanWhether this server supports subscribing to resource updates.
cancel?: object;
list?: object;
requests?: { tools?: { call?: object } };
}
Present if the server supports task-augmented requests.
Optionalcancel?: objectWhether this server supports tasks/cancel.
Optionallist?: objectWhether this server supports tasks/list.
Optionalrequests?: { tools?: { call?: object } }Specifies which request types can be augmented with tasks.
Optionaltools?: { call?: object }Task support for tool-related requests.
Optionalcall?: objectWhether the server supports task-augmented tools/call requests.
Present if the server offers any tools to call.
OptionallistChanged?: booleanWhether this server supports notifications for changes to the tool list.
logging/setLevel
SetLevelRequest
id: RequestId;
jsonrpc: “2.0”;
method: “logging/setLevel”;
params: SetLevelRequestParams;
}
A request from the client to the server, to enable or adjust logging.
SetLevelRequestParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
level: LoggingLevel;
}
Parameters for a logging/setLevel request.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
The level of logging that the client wants to receive from the server. The server should send all logs at this level and higher (i.e., more severe) to the client as notifications/message.
notifications/cancelled
CancelledNotification
jsonrpc: “2.0”;
method: “notifications/cancelled”;
params: CancelledNotificationParams;
}
This notification can be sent by either side to indicate that it is cancelling a previously-issued request.
The request SHOULD still be in-flight, but due to communication latency, it is always possible that this notification MAY arrive after the request has already finished.
This notification indicates that the result will be unused, so any associated processing SHOULD cease.
A client MUST NOT attempt to cancel its initialize request.
For task cancellation, use the tasks/cancel request instead of this notification.
CancelledNotificationParams
_meta?: { [key: string]: unknown };
reason?: string;
requestId?: RequestId;
}
Parameters for a notifications/cancelled notification.
See General fields: _meta for notes on _meta usage.
An optional string describing the reason for the cancellation. This MAY be logged or presented to the user.
The ID of the request to cancel.
This MUST correspond to the ID of a request previously issued in the same direction.
This MUST be provided for cancelling non-task requests.
This MUST NOT be used for cancelling tasks (use the tasks/cancel request instead).
notifications/initialized
InitializedNotification
jsonrpc: “2.0”;
method: “notifications/initialized”;
params?: NotificationParams;
}
This notification is sent from the client to the server after initialization has finished.
notifications/tasks/status
TaskStatusNotification
jsonrpc: “2.0”;
method: “notifications/tasks/status”;
params: TaskStatusNotificationParams;
}
An optional notification from the receiver to the requestor, informing them that a task’s status has changed. Receivers are not required to send these notifications.
TaskStatusNotificationParams
Parameters for a notifications/tasks/status notification.
notifications/message
LoggingMessageNotification
jsonrpc: “2.0”;
method: “notifications/message”;
params: LoggingMessageNotificationParams;
}
JSONRPCNotification of a log message passed from server to client. If no logging/setLevel request has been sent from the client, the server MAY decide which messages to send automatically.
LoggingMessageNotificationParams
_meta?: { [key: string]: unknown };
data: unknown;
level: LoggingLevel;
logger?: string;
}
Parameters for a notifications/message notification.
See General fields: _meta for notes on _meta usage.
The data to be logged, such as a string message or an object. Any JSON serializable type is allowed here.
The severity of this log message.
An optional name of the logger issuing this message.
notifications/progress
ProgressNotification
jsonrpc: “2.0”;
method: “notifications/progress”;
params: ProgressNotificationParams;
}
An out-of-band notification used to inform the receiver of a progress update for a long-running request.
ProgressNotificationParams
_meta?: { [key: string]: unknown };
message?: string;
progress: number;
progressToken: ProgressToken;
total?: number;
}
Parameters for a notifications/progress notification.
See General fields: _meta for notes on _meta usage.
An optional message describing the current progress.
The progress thus far. This should increase every time progress is made, even if the total is unknown.
The progress token which was given in the initial request, used to associate this notification with the request that is proceeding.
Total number of items to process (or total progress required), if known.
notifications/prompts/list_changed
PromptListChangedNotification
jsonrpc: “2.0”;
method: “notifications/prompts/list_changed”;
params?: NotificationParams;
}
An optional notification from the server to the client, informing it that the list of prompts it offers has changed. This may be issued by servers without any previous subscription from the client.
notifications/resources/list_changed
ResourceListChangedNotification
jsonrpc: “2.0”;
method: “notifications/resources/list_changed”;
params?: NotificationParams;
}
An optional notification from the server to the client, informing it that the list of resources it can read from has changed. This may be issued by servers without any previous subscription from the client.
notifications/resources/updated
ResourceUpdatedNotification
jsonrpc: “2.0”;
method: “notifications/resources/updated”;
params: ResourceUpdatedNotificationParams;
}
A notification from the server to the client, informing it that a resource has changed and may need to be read again. This should only be sent if the client previously sent a resources/subscribe request.
ResourceUpdatedNotificationParams
Parameters for a notifications/resources/updated notification.
See General fields: _meta for notes on _meta usage.
The URI of the resource that has been updated. This might be a sub-resource of the one that the client actually subscribed to.
notifications/roots/list_changed
RootsListChangedNotification
jsonrpc: “2.0”;
method: “notifications/roots/list_changed”;
params?: NotificationParams;
}
A notification from the client to the server, informing it that the list of roots has changed. This notification should be sent whenever the client adds, removes, or modifies any root. The server should then request an updated list of roots using the ListRootsRequest.
notifications/tools/list_changed
ToolListChangedNotification
jsonrpc: “2.0”;
method: “notifications/tools/list_changed”;
params?: NotificationParams;
}
An optional notification from the server to the client, informing it that the list of tools it offers has changed. This may be issued by servers without any previous subscription from the client.
notifications/elicitation/complete
ElicitationCompleteNotification
jsonrpc: “2.0”;
method: “notifications/elicitation/complete”;
params: { elicitationId: string };
}
An optional notification from the server to the client, informing it of a completion of a out-of-band elicitation request.
- elicitationId: string
The ID of the elicitation that completed.
ping
PingRequest
A ping, issued by either the server or the client, to check that the other party is still alive. The receiver must promptly respond, or else may be disconnected.
tasks
CreateTaskResult
_meta?: { [key: string]: unknown };
task: Task;
[key: string]: unknown;
}
A response to a task-augmented request.
See General fields: _meta for notes on _meta usage.
RelatedTaskMetadata
Metadata for associating messages with a task.
Include this in the _meta field under the key io.modelcontextprotocol/related-task.
The task identifier this message is associated with.
Task
createdAt: string;
lastUpdatedAt: string;
pollInterval?: number;
status: TaskStatus;
statusMessage?: string;
taskId: string;
ttl: number | null;
}
Data associated with a task.
ISO 8601 timestamp when the task was created.
ISO 8601 timestamp when the task was last updated.
Suggested polling interval in milliseconds.
Current task state.
Optional human-readable message describing the current task state. This can provide context for any status, including:
- Reasons for “cancelled” status
- Summaries for “completed” status
- Diagnostic information for “failed” status (e.g., error details, what went wrong)
The task identifier.
Actual retention duration from creation in milliseconds, null for unlimited.
TaskMetadata
Metadata for augmenting a request with task execution.
Include this in the task field of the request parameters.
Requested duration in milliseconds to retain task from creation.
TaskStatus
The status of a task.
tasks/get
GetTaskRequest
id: RequestId;
jsonrpc: “2.0”;
method: “tasks/get”;
params: { taskId: string };
}
A request to retrieve the state of a task.
- taskId: string
The task identifier to query.
GetTaskResult
The response to a tasks/get request.
tasks/result
GetTaskPayloadRequest
id: RequestId;
jsonrpc: “2.0”;
method: “tasks/result”;
params: { taskId: string };
}
A request to retrieve the result of a completed task.
- taskId: string
The task identifier to retrieve results for.
GetTaskPayloadResult
The response to a tasks/result request. The structure matches the result type of the original request. For example, a tools/call task would return the CallToolResult structure.
See General fields: _meta for notes on _meta usage.
tasks/list
ListTasksRequest
id: RequestId;
jsonrpc: “2.0”;
method: “tasks/list”;
params?: PaginatedRequestParams;
}
A request to retrieve a list of tasks.
ListTasksResult
_meta?: { [key: string]: unknown };
nextCursor?: string;
tasks: Task[];
[key: string]: unknown;
}
The response to a tasks/list request.
See General fields: _meta for notes on _meta usage.
An opaque token representing the pagination position after the last returned result. If present, there may be more results available.
tasks/cancel
CancelTaskRequest
id: RequestId;
jsonrpc: “2.0”;
method: “tasks/cancel”;
params: { taskId: string };
}
A request to cancel a task.
- taskId: string
The task identifier to cancel.
CancelTaskResult
The response to a tasks/cancel request.
prompts/get
GetPromptRequest
id: RequestId;
jsonrpc: “2.0”;
method: “prompts/get”;
params: GetPromptRequestParams;
}
Used by the client to get a prompt provided by the server.
GetPromptRequestParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
arguments?: { [key: string]: string };
name: string;
}
Parameters for a prompts/get request.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
Arguments to use for templating the prompt.
The name of the prompt or prompt template.
GetPromptResult
_meta?: { [key: string]: unknown };
description?: string;
messages: PromptMessage[];
[key: string]: unknown;
}
The server’s response to a prompts/get request from the client.
See General fields: _meta for notes on _meta usage.
An optional description for the prompt.
PromptMessage
Describes a message returned as part of a prompt.
This is similar to SamplingMessage, but also supports the embedding of
resources from the MCP server.
prompts/list
ListPromptsRequest
id: RequestId;
jsonrpc: “2.0”;
method: “prompts/list”;
params?: PaginatedRequestParams;
}
Sent from the client to request a list of prompts and prompt templates the server has.
ListPromptsResult
_meta?: { [key: string]: unknown };
nextCursor?: string;
prompts: Prompt[];
[key: string]: unknown;
}
The server’s response to a prompts/list request from the client.
See General fields: _meta for notes on _meta usage.
An opaque token representing the pagination position after the last returned result. If present, there may be more results available.
Prompt
_meta?: { [key: string]: unknown };
arguments?: PromptArgument[];
description?: string;
icons?: Icon[];
name: string;
title?: string;
}
A prompt or prompt template that the server offers.
See General fields: _meta for notes on _meta usage.
A list of arguments to use for templating the prompt.
An optional description of what this prompt provides
Optional set of sized icons that the client can display in a user interface.
Clients that support rendering icons MUST support at least the following MIME types:
image/png- PNG images (safe, universal compatibility)image/jpeg(andimage/jpg) - JPEG images (safe, universal compatibility)
Clients that support rendering icons SHOULD also support:
image/svg+xml- SVG images (scalable but requires security precautions)image/webp- WebP images (modern, efficient format)
Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn’t present).
Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.
If not provided, the name should be used for display (except for Tool,
where annotations.title should be given precedence over using name,
if present).
PromptArgument
Describes an argument that a prompt can accept.
A human-readable description of the argument.
Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn’t present).
Whether this argument must be provided.
Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.
If not provided, the name should be used for display (except for Tool,
where annotations.title should be given precedence over using name,
if present).
resources/list
ListResourcesRequest
id: RequestId;
jsonrpc: “2.0”;
method: “resources/list”;
params?: PaginatedRequestParams;
}
Sent from the client to request a list of resources the server has.
ListResourcesResult
_meta?: { [key: string]: unknown };
nextCursor?: string;
resources: Resource[];
[key: string]: unknown;
}
The server’s response to a resources/list request from the client.
See General fields: _meta for notes on _meta usage.
An opaque token representing the pagination position after the last returned result. If present, there may be more results available.
Resource
_meta?: { [key: string]: unknown };
annotations?: Annotations;
description?: string;
icons?: Icon[];
mimeType?: string;
name: string;
size?: number;
title?: string;
uri: string;
}
A known resource that the server is capable of reading.
See General fields: _meta for notes on _meta usage.
Optional annotations for the client.
A description of what this resource represents.
This can be used by clients to improve the LLM’s understanding of available resources. It can be thought of like a “hint” to the model.
Optional set of sized icons that the client can display in a user interface.
Clients that support rendering icons MUST support at least the following MIME types:
image/png- PNG images (safe, universal compatibility)image/jpeg(andimage/jpg) - JPEG images (safe, universal compatibility)
Clients that support rendering icons SHOULD also support:
image/svg+xml- SVG images (scalable but requires security precautions)image/webp- WebP images (modern, efficient format)
The MIME type of this resource, if known.
Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn’t present).
The size of the raw resource content, in bytes (i.e., before base64 encoding or any tokenization), if known.
This can be used by Hosts to display file sizes and estimate context window usage.
Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.
If not provided, the name should be used for display (except for Tool,
where annotations.title should be given precedence over using name,
if present).
The URI of this resource.
resources/read
ReadResourceRequest
id: RequestId;
jsonrpc: “2.0”;
method: “resources/read”;
params: ReadResourceRequestParams;
}
Sent from the client to the server, to read a specific resource URI.
ReadResourceRequestParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
uri: string;
}
Parameters for a resources/read request.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
The URI of the resource. The URI can use any protocol; it is up to the server how to interpret it.
ReadResourceResult
_meta?: { [key: string]: unknown };
contents: (TextResourceContents | BlobResourceContents)[];
[key: string]: unknown;
}
The server’s response to a resources/read request from the client.
See General fields: _meta for notes on _meta usage.
resources/subscribe
SubscribeRequest
id: RequestId;
jsonrpc: “2.0”;
method: “resources/subscribe”;
params: SubscribeRequestParams;
}
Sent from the client to request resources/updated notifications from the server whenever a particular resource changes.
SubscribeRequestParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
uri: string;
}
Parameters for a resources/subscribe request.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
The URI of the resource. The URI can use any protocol; it is up to the server how to interpret it.
resources/templates/list
ListResourceTemplatesRequest
id: RequestId;
jsonrpc: “2.0”;
method: “resources/templates/list”;
params?: PaginatedRequestParams;
}
Sent from the client to request a list of resource templates the server has.
ListResourceTemplatesResult
_meta?: { [key: string]: unknown };
nextCursor?: string;
resourceTemplates: ResourceTemplate[];
[key: string]: unknown;
}
The server’s response to a resources/templates/list request from the client.
See General fields: _meta for notes on _meta usage.
An opaque token representing the pagination position after the last returned result. If present, there may be more results available.
ResourceTemplate
_meta?: { [key: string]: unknown };
annotations?: Annotations;
description?: string;
icons?: Icon[];
mimeType?: string;
name: string;
title?: string;
uriTemplate: string;
}
A template description for resources available on the server.
See General fields: _meta for notes on _meta usage.
Optional annotations for the client.
A description of what this template is for.
This can be used by clients to improve the LLM’s understanding of available resources. It can be thought of like a “hint” to the model.
Optional set of sized icons that the client can display in a user interface.
Clients that support rendering icons MUST support at least the following MIME types:
image/png- PNG images (safe, universal compatibility)image/jpeg(andimage/jpg) - JPEG images (safe, universal compatibility)
Clients that support rendering icons SHOULD also support:
image/svg+xml- SVG images (scalable but requires security precautions)image/webp- WebP images (modern, efficient format)
The MIME type for all resources that match this template. This should only be included if all resources matching this template have the same type.
Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn’t present).
Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.
If not provided, the name should be used for display (except for Tool,
where annotations.title should be given precedence over using name,
if present).
A URI template (according to RFC 6570) that can be used to construct resource URIs.
resources/unsubscribe
UnsubscribeRequest
id: RequestId;
jsonrpc: “2.0”;
method: “resources/unsubscribe”;
params: UnsubscribeRequestParams;
}
Sent from the client to request cancellation of resources/updated notifications from the server. This should follow a previous resources/subscribe request.
UnsubscribeRequestParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
uri: string;
}
Parameters for a resources/unsubscribe request.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
The URI of the resource. The URI can use any protocol; it is up to the server how to interpret it.
roots/list
ListRootsRequest
id: RequestId;
jsonrpc: “2.0”;
method: “roots/list”;
params?: RequestParams;
}
Sent from the server to request a list of root URIs from the client. Roots allow servers to ask for specific directories or files to operate on. A common example for roots is providing a set of repositories or directories a server should operate on.
This request is typically used when the server needs to understand the file system structure or access specific locations that the client has permission to read from.
ListRootsResult
_meta?: { [key: string]: unknown };
roots: Root[];
[key: string]: unknown;
}
The client’s response to a roots/list request from the server. This result contains an array of Root objects, each representing a root directory or file that the server can operate on.
See General fields: _meta for notes on _meta usage.
Root
Represents a root directory or file that the server can operate on.
See General fields: _meta for notes on _meta usage.
An optional name for the root. This can be used to provide a human-readable identifier for the root, which may be useful for display purposes or for referencing the root in other parts of the application.
The URI identifying the root. This must start with file:// for now. This restriction may be relaxed in future versions of the protocol to allow other URI schemes.
sampling/createMessage
CreateMessageRequest
id: RequestId;
jsonrpc: “2.0”;
method: “sampling/createMessage”;
params: CreateMessageRequestParams;
}
A request from the server to sample an LLM via the client. The client has full discretion over which model to select. The client should also inform the user before beginning sampling, to allow them to inspect the request (human in the loop) and decide whether to approve it.
CreateMessageRequestParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
includeContext?: “none” | “thisServer” | “allServers”;
maxTokens: number;
messages: SamplingMessage[];
metadata?: object;
modelPreferences?: ModelPreferences;
stopSequences?: string[];
systemPrompt?: string;
task?: TaskMetadata;
temperature?: number;
toolChoice?: ToolChoice;
tools?: Tool[];
}
Parameters for a sampling/createMessage request.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
A request to include context from one or more MCP servers (including the caller), to be attached to the prompt. The client MAY ignore this request.
Default is “none”. Values “thisServer” and “allServers” are soft-deprecated. Servers SHOULD only use these values if the client declares ClientCapabilities.sampling.context. These values may be removed in future spec releases.
The requested maximum number of tokens to sample (to prevent runaway completions).
The client MAY choose to sample fewer tokens than the requested maximum.
Optional metadata to pass through to the LLM provider. The format of this metadata is provider-specific.
The server’s preferences for which model to select. The client MAY ignore these preferences.
An optional system prompt the server wants to use for sampling. The client MAY modify or omit this prompt.
If specified, the caller is requesting task-augmented execution for this request. The request will return a CreateTaskResult immediately, and the actual result can be retrieved later via tasks/result.
Task augmentation is subject to capability negotiation - receivers MUST declare support for task augmentation of specific request types in their capabilities.
Controls how the model uses tools.
The client MUST return an error if this field is provided but ClientCapabilities.sampling.tools is not declared.
Default is { mode: “auto” }.
Tools that the model may use during generation. The client MUST return an error if this field is provided but ClientCapabilities.sampling.tools is not declared.
CreateMessageResult
_meta?: { [key: string]: unknown };
content: SamplingMessageContentBlock | SamplingMessageContentBlock[];
model: string;
role: Role;
stopReason?: string;
[key: string]: unknown;
}
The client’s response to a sampling/createMessage request from the server. The client should inform the user before returning the sampled message, to allow them to inspect the response (human in the loop) and decide whether to allow the server to see it.
See General fields: _meta for notes on _meta usage.
The name of the model that generated the message.
The reason why sampling stopped, if known.
Standard values:
- “endTurn”: Natural end of the assistant’s turn
- “stopSequence”: A stop sequence was encountered
- “maxTokens”: Maximum token limit was reached
- “toolUse”: The model wants to use one or more tools
This field is an open string to allow for provider-specific stop reasons.
ModelHint
Hints to use for model selection.
Keys not declared here are currently left unspecified by the spec and are up to the client to interpret.
A hint for a model name.
The client SHOULD treat this as a substring of a model name; for example:
claude-3-5-sonnetshould matchclaude-3-5-sonnet-20241022sonnetshould matchclaude-3-5-sonnet-20241022,claude-3-sonnet-20240229, etc.claudeshould match any Claude model
The client MAY also map the string to a different provider’s model name or a different model family, as long as it fills a similar niche; for example:
gemini-1.5-flashcould matchclaude-3-haiku-20240307
ModelPreferences
costPriority?: number;
hints?: ModelHint[];
intelligencePriority?: number;
speedPriority?: number;
}
The server’s preferences for model selection, requested of the client during sampling.
Because LLMs can vary along multiple dimensions, choosing the “best” model is rarely straightforward. Different models excel in different areas—some are faster but less capable, others are more capable but more expensive, and so on. This interface allows servers to express their priorities across multiple dimensions to help clients make an appropriate selection for their use case.
These preferences are always advisory. The client MAY ignore them. It is also up to the client to decide how to interpret these preferences and how to balance them against other considerations.
How much to prioritize cost when selecting a model. A value of 0 means cost is not important, while a value of 1 means cost is the most important factor.
Optional hints to use for model selection.
If multiple hints are specified, the client MUST evaluate them in order (such that the first match is taken).
The client SHOULD prioritize these hints over the numeric priorities, but MAY still use the priorities to select from ambiguous matches.
How much to prioritize intelligence and capabilities when selecting a model. A value of 0 means intelligence is not important, while a value of 1 means intelligence is the most important factor.
How much to prioritize sampling speed (latency) when selecting a model. A value of 0 means speed is not important, while a value of 1 means speed is the most important factor.
SamplingMessage
_meta?: { [key: string]: unknown };
content: SamplingMessageContentBlock | SamplingMessageContentBlock[];
role: Role;
}
Describes a message issued to or received from an LLM API.
See General fields: _meta for notes on _meta usage.
ToolChoice
Controls tool selection behavior for sampling requests.
Controls the tool use ability of the model:
- “auto”: Model decides whether to use tools (default)
- “required”: Model MUST use at least one tool before completing
- “none”: Model MUST NOT use any tools
ToolResultContent
_meta?: { [key: string]: unknown };
content: ContentBlock[];
isError?: boolean;
structuredContent?: { [key: string]: unknown };
toolUseId: string;
type: “tool_result”;
}
The result of a tool use, provided by the user back to the assistant.
Optional metadata about the tool result. Clients SHOULD preserve this field when including tool results in subsequent sampling requests to enable caching optimizations.
See General fields: _meta for notes on _meta usage.
The unstructured result content of the tool use.
This has the same format as CallToolResult.content and can include text, images, audio, resource links, and embedded resources.
Whether the tool use resulted in an error.
If true, the content typically describes the error that occurred. Default: false
An optional structured result object.
If the tool defined an outputSchema, this SHOULD conform to that schema.
The ID of the tool use this result corresponds to.
This MUST match the ID from a previous ToolUseContent.
ToolUseContent
_meta?: { [key: string]: unknown };
id: string;
input: { [key: string]: unknown };
name: string;
type: “tool_use”;
}
A request from the assistant to call a tool.
Optional metadata about the tool use. Clients SHOULD preserve this field when including tool uses in subsequent sampling requests to enable caching optimizations.
See General fields: _meta for notes on _meta usage.
A unique identifier for this tool use.
This ID is used to match tool results to their corresponding tool uses.
The arguments to pass to the tool, conforming to the tool’s input schema.
The name of the tool to call.
tools/call
CallToolRequest
id: RequestId;
jsonrpc: “2.0”;
method: “tools/call”;
params: CallToolRequestParams;
}
Used by the client to invoke a tool provided by the server.
CallToolRequestParams
_meta?: { progressToken?: ProgressToken; [key: string]: unknown };
arguments?: { [key: string]: unknown };
name: string;
task?: TaskMetadata;
}
Parameters for a tools/call request.
See General fields: _meta for notes on _meta usage.
- [key: string]: unknown
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.
Arguments to use for the tool call.
The name of the tool.
If specified, the caller is requesting task-augmented execution for this request. The request will return a CreateTaskResult immediately, and the actual result can be retrieved later via tasks/result.
Task augmentation is subject to capability negotiation - receivers MUST declare support for task augmentation of specific request types in their capabilities.
CallToolResult
_meta?: { [key: string]: unknown };
content: ContentBlock[];
isError?: boolean;
structuredContent?: { [key: string]: unknown };
[key: string]: unknown;
}
The server’s response to a tool call.
See General fields: _meta for notes on _meta usage.
A list of content objects that represent the unstructured result of the tool call.
Whether the tool call ended in an error.
If not set, this is assumed to be false (the call was successful).
Any errors that originate from the tool SHOULD be reported inside the result
object, with isError set to true, not as an MCP protocol-level error
response. Otherwise, the LLM would not be able to see that an error occurred
and self-correct.
However, any errors in finding the tool, an error indicating that the server does not support tool calls, or any other exceptional conditions, should be reported as an MCP error response.
An optional JSON object that represents the structured result of the tool call.
tools/list
ListToolsRequest
id: RequestId;
jsonrpc: “2.0”;
method: “tools/list”;
params?: PaginatedRequestParams;
}
Sent from the client to request a list of tools the server has.
ListToolsResult
_meta?: { [key: string]: unknown };
nextCursor?: string;
tools: Tool[];
[key: string]: unknown;
}
The server’s response to a tools/list request from the client.
See General fields: _meta for notes on _meta usage.
An opaque token representing the pagination position after the last returned result. If present, there may be more results available.
Tool
_meta?: { [key: string]: unknown };
annotations?: ToolAnnotations;
description?: string;
execution?: ToolExecution;
icons?: Icon[];
inputSchema: {
$schema?: string;
properties?: { [key: string]: object };
required?: string[];
type: “object”;
};
name: string;
outputSchema?: {
$schema?: string;
properties?: { [key: string]: object };
required?: string[];
type: “object”;
};
title?: string;
}
Definition for a tool the client can call.
See General fields: _meta for notes on _meta usage.
Optional additional tool information.
Display name precedence order is: title, annotations.title, then name.
A human-readable description of the tool.
This can be used by clients to improve the LLM’s understanding of available tools. It can be thought of like a “hint” to the model.
Execution-related properties for this tool.
Optional set of sized icons that the client can display in a user interface.
Clients that support rendering icons MUST support at least the following MIME types:
image/png- PNG images (safe, universal compatibility)image/jpeg(andimage/jpg) - JPEG images (safe, universal compatibility)
Clients that support rendering icons SHOULD also support:
image/svg+xml- SVG images (scalable but requires security precautions)image/webp- WebP images (modern, efficient format)
$schema?: string;
properties?: { [key: string]: object };
required?: string[];
type: “object”;
}
A JSON Schema object defining the expected parameters for the tool.
Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn’t present).
$schema?: string;
properties?: { [key: string]: object };
required?: string[];
type: “object”;
}
An optional JSON Schema object defining the structure of the tool’s output returned in the structuredContent field of a CallToolResult.
Defaults to JSON Schema 2020-12 when no explicit $schema is provided. Currently restricted to type: “object” at the root level.
Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.
If not provided, the name should be used for display (except for Tool,
where annotations.title should be given precedence over using name,
if present).
ToolAnnotations
destructiveHint?: boolean;
idempotentHint?: boolean;
openWorldHint?: boolean;
readOnlyHint?: boolean;
title?: string;
}
Additional properties describing a Tool to clients.
NOTE: all properties in ToolAnnotations are hints.
They are not guaranteed to provide a faithful description of
tool behavior (including descriptive properties like title).
Clients should never make tool use decisions based on ToolAnnotations received from untrusted servers.
If true, the tool may perform destructive updates to its environment. If false, the tool performs only additive updates.
(This property is meaningful only when readOnlyHint == false)
Default: true
If true, calling the tool repeatedly with the same arguments will have no additional effect on its environment.
(This property is meaningful only when readOnlyHint == false)
Default: false
If true, this tool may interact with an “open world” of external entities. If false, the tool’s domain of interaction is closed. For example, the world of a web search tool is open, whereas that of a memory tool is not.
Default: true
If true, the tool does not modify its environment.
Default: false
A human-readable title for the tool.
ToolExecution
Execution-related properties for a tool.
Indicates whether this tool supports task-augmented execution. This allows clients to handle long-running operations through polling the task system.
- “forbidden”: Tool does not support task-augmented execution (default when absent)
- “optional”: Tool may support task-augmented execution
- “required”: Tool requires task-augmented execution
Default: “forbidden”
A response to a request that indicates an error occurred.