MCP spec conformance: 7 requirements violated (via @hasmcp/mcp-spec-test) — spec 2026-07-28

[hasmcp-dev]

Running the black-box @hasmcp/mcp-spec-test conformance suite against the simple-tool example server from this repo (via uvx) found 7 spec violations when negotiating the newest supported revision (2026-07-28). The root cause across most failures is that the server does not implement the server/discover method at all (Method not found), which this revision's test suite treats as required; there is also one version-negotiation case where a version-less tools/list is rejected instead of being served on the default revision. For contrast, re-running the same suite pinned to the older 2025-11-25 revision produced zero failures, so this appears specific to 2026-07-28 support (the official SDK client itself doesn't yet implement that newest revision either, per the "Official SDK interop" passes below, so this may simply reflect that 2026-07-28 support is still in progress rather than a regression).

Conformance report

MCP 2026-07-28 conformance report

Verdict: not conformant — 7 requirements violated.

Target	uvx --from 'git+https://github.com/modelcontextprotocol/python-sdk#subdirectory=examples/servers/simple-tool' mcp-simple-tool
Transport	stdio
Revision tested	2026-07-28
Revisions supported	2026-07-28, 2025-11-25
Passed	7
Failed	7
Not verified	22
Cases applied	36
Duration	22604ms
Generated	2026-08-24T09:25:00.186Z
Tool	@hasmcp/mcp-spec-test 0.1.1

Failed (7)

the server deviates from the spec here

server/discover

• server/discover is answered without a session or handshake
  expected 200, got 0: {"_raw":"no response within 10000ms"}

0 !== 200

• server/discover advertises the versions the server can serve
  server/discover unexpected JSON-RPC error: {"code":-32601,"message":"Method not found","data":"server/discover"}
• server/discover is a CacheableResult with usable cache hints
  server/discover unexpected JSON-RPC error: {"code":-32601,"message":"Method not found","data":"server/discover"}
• server/discover reports server identity and capabilities
  server/discover unexpected JSON-RPC error: {"code":-32601,"message":"Method not found","data":"server/discover"}
• server/discover is stable across calls within its own TTL
  server/discover unexpected JSON-RPC error: {"code":-32601,"message":"Method not found","data":"server/discover"}
• server/discover advertises a revision this suite supports
  server/discover unexpected JSON-RPC error: {"code":-32601,"message":"Method not found","data":"server/discover"}

Version negotiation

• a request with no version at all is served on the default
  a version-less tools/list must be served, not refused: {"code":-32602,"message":"Invalid request parameters","data":""}

Not verified (22)

skipped; a skip is not a pass

Capability methods

• tools/list returns schema-conformant tools
  cannot determine what the target supports — server/discover returned no result (status 0)
• tools/call on an unknown tool is an error, not a crash
  cannot determine what the target supports — server/discover returned no result (status 0)
• tools/call returns a schema-conformant CallToolResult
  cannot determine what the target supports — server/discover returned no result (status 0)
• prompts/list returns schema-conformant prompts
  cannot determine what the target supports — server/discover returned no result (status 0)
• prompts/get returns messages with a role and content
  cannot determine what the target supports — server/discover returned no result (status 0)
• resources/list returns schema-conformant resources
  cannot determine what the target supports — server/discover returned no result (status 0)
• resources/templates/list returns schema-conformant templates
  cannot determine what the target supports — server/discover returned no result (status 0)
• resources/read returns contents for every sampled resource
  cannot determine what the target supports — server/discover returned no result (status 0)
• resources/read on an unknown uri is an error
  cannot determine what the target supports — server/discover returned no result (status 0)
• following nextCursor terminates and does not repeat a page
  cannot determine what the target supports — server/discover returned no result (status 0)
• an invalid pagination cursor is rejected (SHOULD)
  cannot determine what the target supports — server/discover returned no result (status 0)

Version negotiation

• a version declared in _meta is accepted
  cannot determine what the target supports — server/discover returned no result (status 0)
• an unsupported version is rejected with the supported list
  cannot determine what the target supports — server/discover returned no result (status 0)
• clientInfo is optional (SHOULD, not MUST)
  cannot determine what the target supports — server/discover returned no result (status 0)

Result envelope

• every result carries the required resultType
  cannot determine what the target supports — server/discover returned no result (status 0)
• cacheable list results carry the schema-required cache hints
  cannot determine what the target supports — server/discover returned no result (status 0)
• results identify the server in _meta
  cannot determine what the target supports — server/discover returned no result (status 0)
• a client on an older version receives no newer-revision fields
  cannot determine what the target supports — server/discover returned no result (status 0)

subscriptions/listen

• subscriptions/listen acknowledges only the opted-in notification types
  cannot determine what the target supports — server/discover returned no result (status 0)
• the acknowledgment carries the subscription id for correlation
  cannot determine what the target supports — server/discover returned no result (status 0)
• a listen requesting no notification types is not a subscription to everything
  cannot determine what the target supports — server/discover returned no result (status 0)
• a cancelled subscription ends with a conformant teardown result, if it sends one
  cannot determine what the target supports — server/discover returned no result (status 0)

Passed (7)

checked and conformant

server/discover

• the suite is reading a schema that matches the features it selected

Result envelope

• schema sanity: the envelope fields match the features selected

Official SDK interop

• the official SDK does not yet implement the newest revision
• a stock official-SDK client completes the handshake
• the handshake settles on a revision inside the supported window
• a stock official-SDK client can list tools

subscriptions/listen

• schema sanity: SubscriptionsListenResult requires _meta and resultType

How to reproduce

With Docker:

docker pull hasmcp/mcp-spec-test:latest
docker run --rm hasmcp/mcp-spec-test -c "uvx --from 'git+https://github.com/modelcontextprotocol/python-sdk#subdirectory=examples/servers/simple-tool' mcp-simple-tool" --spec-version 2026-07-28

Without Docker (npx):

npx @hasmcp/mcp-spec-test@latest -c "uvx --from 'git+https://github.com/modelcontextprotocol/python-sdk#subdirectory=examples/servers/simple-tool' mcp-simple-tool" --spec-version 2026-07-28

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This issue was generated by an automated MCP conformance sweep across public MCP server repos. If this turns out to be a false positive (e.g. an artifact of the test container's environment, or the newest spec revision simply not being a target for this SDK yet), feel free to close it — no offense taken.