Whether a cached tool list defeats a change notification

See also

Sources

1. 1
   If the time-to-live field is absent, clients should assume a default of 0, treat the response as immediately stale, and rely on their own caching heuristics or on notifications.

   Model Context Protocol specification 2026-07-28, Caching · Time-to-Live (TTL) Field, bullet 3 · Checked 2026-09-05
2. 2
   The Model Context Protocol caching specification requires servers to provide a time-to-live value of 0 or greater whenever they include a TTL field.

   Model Context Protocol specification 2026-07-28, Caching · Time-to-Live (TTL) Field, bullet 3 · Checked 2026-09-05
3. 3
   A server that computes a per-caller tools list and marks the response with a public cache scope would let one caller's authorized tool set be served to another caller from a shared cache.inferred

   Model Context Protocol specification 2026-07-28, Caching · Security Considerations combined with the server tools Capabilities section · Checked 2026-09-05
4. 4
   The caching page's own sequence diagram walks through a tools list cache being invalidated by a notifications/tools/list_changed message before the time-to-live expires.

   Model Context Protocol specification 2026-07-28, Caching · Mermaid sequence diagram following Interaction with Notifications, read from the raw body · Checked 2026-09-05
5. 5
   The caching page's sequence diagram illustrates the tools-list cache-invalidation scenario using an example time-to-live of 300000 milliseconds, which is illustrative rather than a specified default.

   Model Context Protocol specification 2026-07-28, Caching · Mermaid sequence diagram following Interaction with Notifications, read from the raw body · Checked 2026-09-05
6. 6
   In the sentence that connects notification to cache invalidation, the word invalidates is bolded and the following should is lowercase and unstyled, unlike every other RFC 2119 keyword on the page.field report

   Model Context Protocol specification 2026-07-28, Caching · Interaction with Notifications, closing paragraph, raw markup · Checked 2026-09-05
7. 7
   The caching page publishes a floor for the time-to-live field and no ceiling and no recommended default magnitude for any cacheable operation.

   Model Context Protocol specification 2026-07-28, Caching · Time-to-Live (TTL) Field, whole section · Checked 2026-09-05
8. 8
   None of the 4 specification pages states what a client should, must or may do on determining that it missed a list changed notification.

   Model Context Protocol specification 2026-07-28, Caching · Whole documents: caching, server tools, subscriptions, resources · Checked 2026-09-05
9. 9
   The Model Context Protocol caching page states that a relevant notification received while a cached response is still fresh invalidates that cached response, which should then be considered immediately stale.

   Model Context Protocol specification 2026-07-28, Caching · Interaction with Notifications, closing paragraph · Checked 2026-09-05
10. 10
    The caching page's Interaction with Notifications section never uses the words subscribe, subscription or subscriptions/listen; it names listChanged and notification and never names the mechanism that delivers them.

    Model Context Protocol specification 2026-07-28, Caching · Interaction with Notifications section · Checked 2026-09-05
11. 11
    The caching page states that a response marked with a public cache scope may be shared between callers even when it came from an authenticated endpoint, and its worked example is an authenticated tools list call.

    Model Context Protocol specification 2026-07-28, Caching · Security Considerations, opening paragraph · Checked 2026-09-05
12. 12
    A server may provide a time-to-live without advertising listChanged, in which case the client relies entirely on time-to-live freshness with no invalidation signal at all.

    Model Context Protocol specification 2026-07-28, Caching · Interaction with Notifications, bullet 1 · Checked 2026-09-05
13. 13
    A client whose requested toolsListChanged filter is silently dropped from the subscription acknowledgment receives no notification, so the caching page's invalidation scenario never applies to it even though the server advertised listChanged.inferred

    Model Context Protocol specification 2026-07-28, Subscriptions · Acknowledgment section combined with the caching page's Interaction with Notifications · Checked 2026-09-05
14. 14
    The tools list result set may vary by the authorization presented on the request, because credentials are per-request input rather than connection state.

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

Documents

Cite this page

WarmTransfer. (2026, September 5). Whether a cached tool list defeats a change notification. WarmTransfer. https://warmtransfer.net/knowledge/mcp-cache-versus-notification

@misc{warmtransfer-mcp-cache-versus-notification,
  title  = {Whether a cached tool list defeats a change notification},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/mcp-cache-versus-notification},
  note   = {Verified 2026-09-05}
}