Stateful tools in the Model Context Protocol

See also

Sources

1. 1
   Because the Message Flow section of the Tools page is diagram-only in both 2025-11-25 and 2026-07-28, an extraction that removes mermaid blocks leaves that section empty in both revisions and a comparison of the two extractions shows no change there, although the diagrams differ.inferred

   Model Context Protocol specification 2026-07-28, Server Features: Tools · Message Flow (compared with the same section of mcp-spec-2025-11-25-server-tools) · Checked 2026-09-30
2. 2
   The Stateful Tools example on the 2026-07-28 Tools page is a jsonc block containing comments and three separate objects, so it is complete as published yet is not a single valid JSON document.

   Model Context Protocol specification 2026-07-28, Server Features: Tools · Stateful Tools, jsonc block · Checked 2026-09-30
3. 3
   In the MCP 2025-11-25 Tools page, the Message Flow section consists of a single mermaid sequenceDiagram code block and contains no prose.

   Model Context Protocol specification 2025-11-25, Server Features: Tools · Message Flow · Checked 2026-09-30
4. 4
   The 2025-11-25 Tools Message Flow diagram shows the update steps without an opt block and without any subscriptions/listen or acknowledgement message: the server sends tools/list_changed and the client then calls tools/list.

   Model Context Protocol specification 2025-11-25, Server Features: Tools · Message Flow, mermaid block, 'Updates' note · Checked 2026-09-30
5. 5
   As served on 2026-09-30 the 2026-07-28 Tools page contained 23 json blocks, 1 jsonc block and 1 mermaid block, every fence was closed, and the document ended with the list item 'Log tool usage for audit purposes'.

   Model Context Protocol specification 2026-07-28, Server Features: Tools · whole page; final line under Security Considerations · Checked 2026-09-30
6. 6
   In the MCP 2026-07-28 Tools page, the Message Flow section consists of a single mermaid sequenceDiagram code block and contains no prose.

   Model Context Protocol specification 2026-07-28, Server Features: Tools · Message Flow · Checked 2026-09-30
7. 7
   The 2026-07-28 Tools Message Flow diagram places the update steps inside an 'opt listChanged' block in which the client first sends subscriptions/listen (toolsListChanged: true) and the server sends notifications/subscriptions/acknowledged before notifications/tools/list_changed.

   Model Context Protocol specification 2026-07-28, Server Features: Tools · Message Flow, mermaid block, 'opt listChanged' group · Checked 2026-09-30
8. 8
   Because legacy clients have no fall-forward mechanism, a server that must keep existing initialize-based integrations working while adopting 2026-07-28 has to be dual-era rather than modern-only, and it may serve both eras concurrently on one endpoint.inferred

   Model Context Protocol specification 2026-07-28, Versioning and Compatibility · Compatibility Matrix; Backward Compatibility with Initialization-Based Versions · Checked 2026-09-16
9. 9
   Because MCP is stateless and has no protocol-level sessions, servers that need state mint explicit handles, and servers implementing authorization MUST verify all inbound requests and MUST NOT treat possession of a state handle as authentication.

   Model Context Protocol specification 2026-07-28, Security Best Practices · State Handle Hijacking · Checked 2026-09-16
10. 10
    The Tools page grew by roughly half between the 2025-11-25 and 2026-07-28 revisions and the change is almost entirely additive.field report

    Model Context Protocol specification 2026-07-28, Server Features: Tools · Tools page compared across the two revisions · Checked 2026-09-05
11. 11
    The deprecated features registry states that no features have been removed under the policy yet while the changelog for the same revision lists removals.disputed

    Model Context Protocol specification 2026-07-28, Deprecated Features · Deprecated Features registry compared with Key Changes · Checked 2026-09-05
12. 12
    The specification changelog announces a minimum 12 month deprecation window.disputed

    Model Context Protocol specification 2026-07-28, Key Changes · Key Changes, deprecation policy · Checked 2026-09-05
13. 13
    The recommendation that servers return tools in a deterministic order is new in the 2026-07-28 revision and does not appear in the 2025-11-25 revision.

    Model Context Protocol specification 2025-11-25, Server Features: Tools · Tools page compared across the two revisions · Checked 2026-09-05
14. 14
    The execution and task support fields present in the 2025-11-25 Tools page are removed in the 2026-07-28 revision.

    Model Context Protocol specification 2026-07-28, Server Features: Tools · Tools page compared across the two revisions · Checked 2026-09-05
15. 15
    Multi Round-Trip Requests are designed to work without requiring a shared storage layer across server instances or stateful load balancing.

    Model Context Protocol specification 2026-07-28, Multi Round-Trip Requests · Multi Round-Trip Requests · Checked 2026-09-05
16. 16
    Multi Round-Trip Requests do not share the long-lived connection machinery that subscriptions use.inferred

    Model Context Protocol specification 2026-07-28, Multi Round-Trip Requests · Multi Round-Trip Requests · Checked 2026-09-05
17. 17
    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.

    Model Context Protocol specification 2025-11-25, Server Features: Tools · Tools page compared across the two revisions · Checked 2026-09-05
18. 18
    The Stateful Tools section contains no RFC 2119 keywords at all; MUST SHOULD MAY REQUIRED and SHALL each occur 0 times within it.

    Model Context Protocol specification 2026-07-28, Server Features: Tools · Tools > Stateful Tools · Checked 2026-09-05
19. 19
    The specification states that the protocol has no concept of a state handle and that from the wire's perspective a handle is an ordinary string in a tool result and an ordinary argument to subsequent tool calls.

    Model Context Protocol specification 2026-07-28, Server Features: Tools · Tools > Stateful Tools · Checked 2026-09-05
20. 20
    The specification reconciles stateful tools with the rule that a tool set must not vary per connection: the invariance rule binds the tools list operation while handles vary the tool call.

    Model Context Protocol specification 2026-07-28, Server Features: Tools · Tools > overview paragraph read together with Stateful Tools · Checked 2026-09-05
21. 21
    The Model Context Protocol's Stateful Tools section declares itself non-normative guidance for tool design.

    Model Context Protocol specification 2026-07-28, Server Features: Tools · Tools > Stateful Tools · Checked 2026-09-05
22. 22
    The deprecated features registry gives HTTP with server-sent events an earliest removal of 3 months after a proposal reaches Final, and does not publish that date.disputed

    Model Context Protocol specification 2026-07-28, Deprecated Features · Deprecated Features registry · Checked 2026-09-05
23. 23
    The specification does not state what state a stateful tool holds who holds it or for how long, nor what happens to it when a connection drops.

    Model Context Protocol specification 2026-07-28, Server Features: Tools · Tools > Stateful Tools · Checked 2026-09-05
24. 24
    Statefulness in Model Context Protocol tools is a design convention carried in ordinary tool arguments and results rather than a protocol mechanism.inferred

    Model Context Protocol specification 2026-07-28, Server Features: Tools · Tools > Stateful Tools · Checked 2026-09-05

Documents

Cite this page

WarmTransfer. (2026, September 30). 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 2026-09-30}
}