Documentation Index

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Filesystems Charter

Charter for the MCP Filesystems Working Group.

Group Type

Working Group

Mission Statement

The Filesystems Working Group exists to make MCP Resources bidirectional, so that an agent can write a result back to the server it reads its inputs from. Agent platforms are converging on presenting services to models as filesystems, and Resources already addresses content by URI under a file:// scheme the specification defines as identifying “resources that behave like a filesystem”. Currently, Resources carries that surface in the read direction. The WG will produce a single Extensions Track SEP covering write operations, optimistic concurrency control, and the interaction with change notification and caching.

Scope

In Scope

• Specification Work: One Extensions Track SEP, provisionally titled Filesystem Operations for Resources, covering:
  1. Operations. Define create, update, delete, and a metadata read (stat) that answers existence, size and last-modified for one URI without fetching the body.
  2. Optimistic concurrency control. Specify how two writers avoid a lost update, and how a client creates a resource under a create-if-absent precondition.
  3. Change notification and caching. Specify how a write interacts with notifications/resources/updated, the time-to-live and cache scope fields ttlMs and cacheScope, and the lastModified annotation.
• Cross-Cutting Concerns: Reconcile the proposals that extend this primitive into one coherent design. SEP-2571, Resource Submission for Agent Coordination proposes resources/create and resources/delete. SEP-2532, Resource Streaming for Binary Content Delivery proposes resources/stream. SEP-1708, MCP Client-Brokered Filesystem Access proposed a files/* method family standing beside Resources, and closed on 23 January 2026.
• Documentation: Document the new operations in the specification, and give server authors guidance on choosing between a resource write path and a tool-based one.

Out of Scope

• A parallel files/* primitive standing beside Resources. The WG broadens the existing Resources primitive.
• Host-side sandbox and local-disk semantics. The WG standardizes the client and server wire format. How a host materializes resources into a filesystem for the model stays a host concern.
• Authorization policy for writes, beyond stating where the existing MCP authorization specification applies.

Related Groups

• File Uploads WG. Both groups transfer content to a server. Coordination needed on where an upload-oriented flow ends and a resource write operation begins.
• Skills Over MCP WG. Filesystem dependency, including questions about write access, was an agenda item at the office hours of 24 March 2026 and remains open.
• Agents WG. Multi-agent and job orchestration systems are the motivating consumers of a shared write path.

Leadership

Authority & Decision Rights

Membership

Operations

Discord: #filesystems-wg.

Note The cadence above is provisional. This is subject to change once the first working session sets it.

Deliverables & Success Metrics

Active Work Items

The group’s first act is to take up SEP-2571 with its author, since it already covers create and delete.

Success Criteria

• An accepted Extensions Track SEP covering create, update, delete and stat, with a defined optimistic concurrency control mechanism and a specified interaction with notifications/resources/updated, ttlMs, cacheScope and lastModified.
• Each proposal in this space resolved. SEP-2571 and SEP-2532 are open at time of writing, and each should end up folded in, superseded, or explicitly scoped out.
• Reference implementations in at least two Tier 1 SDKs.
• Two independent server implementations exercising the write path against a common client.

Changelog

Last updated Oct 08, 2026