Why
r/mcp feedback (2026-08): a server can keep tools/list identical and still swap behavior at call time (args, time, client). The listing fingerprint is a strong tripwire for postmark-mcp; it is not proof of a stable server.
Also worth instrumenting argument validation on tools/call, not only the listing: silent mid-call behavior change is where users get bitten.
Constraints
- Do not store tool descriptions or response bodies on the wire / in forwarded events (poisoned description must not become a surveillance feed)
- Prefer hashes / shape digests over content
Proposal (design first)
- Optional response-shape digest on
tools/call results
- Optional arg-validation / error-class drift signals
- Document that a quiet listing digest is not a stable-server claim (README update tracked separately)
Source
https://www.reddit.com/r/mcp/comments/1vvinyo/
Why
r/mcp feedback (2026-08): a server can keep
tools/listidentical and still swap behavior at call time (args, time, client). The listing fingerprint is a strong tripwire for postmark-mcp; it is not proof of a stable server.Also worth instrumenting argument validation on
tools/call, not only the listing: silent mid-call behavior change is where users get bitten.Constraints
Proposal (design first)
tools/callresultsSource
https://www.reddit.com/r/mcp/comments/1vvinyo/