Working Group
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.
- Specification Work: One Extensions Track SEP, provisionally titled Filesystem Operations for Resources, covering:
- Operations. Define create, update, delete, and a metadata read (
stat) that answers existence, size and
last-modified for one URI without fetching the body.
- Optimistic concurrency control. Specify how two writers avoid a lost update, and how a client creates a
resource under a create-if-absent precondition.
- 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.
- 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.
- 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. The published
Skills extension uses Resources for file reads and defines optional directory reading.
It does not depend on filesystem write operations; coordinate on future resource operations that affect skills.
- Agents IG. Multi-agent and job orchestration systems are the motivating consumers of a shared write path.
Discord: #filesystems-wg.
Note The cadence above is provisional. This is subject to change once the first working session sets it.
The group's first act is to take up SEP-2571 with its author, since it already covers create and delete.
- 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.