Stateful tools in the Model Context Protocol

Verified 2026-09-05 · 15 claims · sources tier 1 · 3 disputed

Also known as MRTR, Multi Round-Trip Requests, state handle, stateful tools.

The Model Context Protocol defines guidance for designing stateful tools within its server features specification 12. WarmTransfer's reading of the sources is that statefulness in Model Context Protocol tools functions as a design convention carried in ordinary tool arguments and results rather than a protocol mechanism 15.

How stateful tools work

The Stateful Tools section of the Model Context Protocol declares itself non-normative guidance for tool design 12. Furthermore, this section contains no RFC 2119 keywords; MUST, SHOULD, MAY, REQUIRED, and SHALL each occur zero times within it 9. The protocol itself has no concept of a state handle 10. Instead, from the perspective of the wire, a handle is simply an ordinary string returned in a tool result and passed as an ordinary argument to subsequent tool calls 10.

The specification reconciles stateful tools with the baseline rule that a tool set must not vary per connection: the invariance rule applies strictly to the tools list operation, whereas handles vary the arguments of the tool call itself 11. However, the specification does not state what state a stateful tool holds, who holds it, how long it is retained, or what happens to that state when a connection drops 14.

Protocol evolution and changes across revisions

In the field, reports suggest that the Tools page grew by roughly half between the 2025-11-25 and 2026-07-28 revisions, with the expansion being almost entirely additive 1. Comparison across the revisions reveals several modifications to tool constraints and fields 8​4​5:

• The requirement that a server's tool set must not vary per connection is new in the 2026-07-28 revision and does not appear in the 2025-11-25 revision 8.
• The recommendation that servers return tools in a deterministic order is also new in the 2026-07-28 revision and is absent from the 2025-11-25 revision 4.
• Execution and task support fields that were present in the 2025-11-25 Tools page were removed in the 2026-07-28 revision 5.

Multi Round-Trip Requests and state handling

Multi Round-Trip Requests are designed to function without requiring a shared storage layer across server instances or stateful load balancing 6. WarmTransfer's reading of the sources is that Multi Round-Trip Requests do not share the long-lived connection machinery used by The MCP subscriptions listen stream and notification delivery 7.

Deprecation policy discrepancies

Sources disagree on the deprecation rules and timelines across specification sections 3​13​2. Sources disagree on the length of deprecation windows: the changelog announces a minimum twelve-month deprecation window 3, yet the deprecated features registry gives HTTP with server-sent events an earliest removal of three months after a proposal reaches Final without publishing that date 13. In addition, this is disputed by internal registry statements: the deprecated features registry claims that no features have been removed under the policy yet, even while the changelog for that exact revision lists removals 2.

Applicability

Across the claims in this article, the evidence covers Model Context Protocol, verified as of 2026-09-05. The deployment model is not covered by any claim in this article. Specific rules and comparisons apply to specification revision 2025-11-25 8​4 and revision 2026-07-28 12​9​10​14​11​5​6.

What remains uncertain

The specific extension to which tasks moved following their removal from the Tools page is not covered by any claim in this article. Whether the corpus extractor drops diagrams or truncates code blocks during documentation processing is not covered by any claim in this article. Whether any Webex published MCP servers for external AI clients expose stateful tools is not covered by any claim in this article. Whether a state handle can be forged or replayed by an unauthorized party is not covered by any claim in this article. The contents and features of Discovery in the Model Context Protocol introduced as a new page in this revision are not covered by any claim in this article. The detailed protocol mechanism governing Multi Round-Trip Requests beyond its avoidance of shared storage is not covered by any claim in this article. The specification details surrounding Model Context Protocol resources and the caching utility are not covered by any claim in this article. How long a state handle lives and who stores it is not covered by any claim in this article.

WarmTransfer. (2026, September 5). Stateful tools in the Model Context Protocol. WarmTransfer. https://warmtransfer.net/knowledge/mcp-stateful-tools

@misc{warmtransfer-mcp-stateful-tools,
  title  = {Stateful tools in the Model Context Protocol},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/mcp-stateful-tools},
  note   = {Verified 2026-09-05}
}