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Copy page Copy page ​ Group Type Working Group ​ 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 . ​ Scope ​ 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. ​ 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. ​ 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. ​ Leadership Role Name Organization GitHub Term Lead Den Delimarsky Anthropic @localden Initial Sponsored by Den Delimarsky ( @localden ) and Nick Cooper ( @nickcoai ). ​ Authority & Decision Rights Decision Type Authority Level Meeting logistics & scheduling WG Leads (autonomous) Proposal prioritization within WG WG Leads (autonomous) SEP triage & closure (in scope) WG Leads (autonomous, with documented rationale) Technical design within scope WG consensus Spec changes (additive) WG consensus → Core Maintainer approval Spec changes (breaking/fundamental) WG consensus → Core Maintainer approval + wider review Scope expansion Core Maintainer approval required WG Member approval WG Member sponsors ​ Membership Name Organization GitHub Discord Level Den Delimarsky Anthropic @localden Lead Nick Cooper OpenAI @nickcoai WG Member Olivier Chafik Anthropic @ochafik WG Member ​ Operations Meeting Frequency Duration Purpose Working Session Biweekly 30 min Technical discussion, proposal review Discord: #file-uploads-wg ​ Deliverables & Success Metrics ​ Active Work Items Item Status Target Date Champion SEP-2356: Declarative file inputs Draft End May @ochafik TypeScript SDK reference implementation — End May @ochafik Reference implementation in a second Tier-1 SDK — End June TBD ​ 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. ​ Changelog Date Change 2026-04-23 Initial charter Was this page helpful? 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