File Uploads Charter

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Group Type

Working Group

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Mission Statement

The File Uploads Working Group exists to define how MCP tools and elicitation requests declare file inputs so that hosts can present native file pickers and pass user-selected file content to servers. Today, servers that need a file from the user resort to prose instructions asking for base64 strings or local paths, which produces inconsistent UX and pushes encoding details onto end users. This WG will specify a minimal, schema-level mechanism for declaring file inputs and the wire format for delivering them, anchored on SEP-2356.

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Scope

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In Scope

• Specification Work: SEPs defining declarative file input descriptors on tool input schemas and elicitation request schemas, the wire encoding for file content, and host-side handling requirements.
• Reference Implementations: SDK types and helpers for FileInputDescriptor, data URI encoding, and a sample host flow demonstrating picker invocation and value substitution.
• Cross-Cutting Concerns: Coordination with the MCP Apps WG where embedded UI surfaces present their own file pickers, and with the Security WG on host-side validation requirements.
• Documentation: Specification sections covering file input declaration and a migration guide for servers currently using ad-hoc base64 instructions.

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Out of Scope

• Server-to-client file delivery, which is already covered by Resources and BlobResourceContents.
• Changes to the transport layer or session model.

The WG may evaluate approaches such as streaming, chunked transfer, or presigned upload URLs as part of its design work; whether those land in the initial SEP or a follow-up is a WG decision rather than a charter constraint.

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Related Groups

• MCP Apps WG — embedded app UIs may surface their own file pickers; the descriptor format should be reusable in that context.
• Security WG — host-side validation requirements for user-supplied file content (the SEP references OWASP ASVS V5 for general upload hygiene).
• Tool Annotations IG — file input descriptors are a form of input-parameter metadata and should remain consistent with the broader annotation taxonomy.

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Leadership

Sponsored by Den Delimarsky (@localden) and Nick Cooper (@nickcoai).

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Authority & Decision Rights

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Membership

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Operations

Discord: #file-uploads-wg

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Deliverables & Success Metrics

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Active Work Items

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Success Criteria

• An accepted SEP defining the file input descriptor and wire encoding.
• Reference implementations in at least two Tier-1 SDKs.
• At least one production host rendering a native file picker from the descriptor.
• Conformance test coverage for the new schema keyword.

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Changelog