MCP spec conformance: 10 requirement(s) violated (via @hasmcp/mcp-spec-test) — spec 2026-07-28

[hasmcp-dev]

Running the black-box @hasmcp/mcp-spec-test conformance suite against opfor's MCP server (built from source per the README: npm install && npm run build --workspaces --if-present then node runners/mcp/dist/index.js) shows the server printing a plaintext startup banner to stdout before any JSON-RPC traffic — specifically ◇ injected env (0) from .env // tip: ⌘ enable debugging { debug: true } — which corrupts the stdio JSON-RPC framing that MCP clients expect on that stream. As a result, the process gets torn down before the handshake completes ("server exited"), the official-SDK client sees the connection close, and 22 further checks can't be verified. This is a genuine framing bug rather than a test-environment artifact: on stdio transport, MCP servers must not write anything but JSON-RPC messages to stdout, and this banner (presumably a startup-logging/env-loader library) is doing exactly that.

Conformance report

MCP 2026-07-28 conformance report

Verdict: not conformant — 10 requirements violated.

Target	sh -c '[ -d agent-opfor ] || git clone https://github.com/KeyValueSoftwareSystems/agent-opfor && cd agent-opfor && npm install && npm run build --workspaces --if-present && node runners/mcp/dist/index.js'
Transport	stdio
Revision tested	2026-07-28
Revisions supported	2026-07-28, 2025-11-25
Passed	4
Failed	10
Not verified	22
Cases applied	36
Duration	21347ms
Generated	2026-08-24T14:16:27.016Z
Tool	@hasmcp/mcp-spec-test 0.1.1

Failed (10)

the server deviates from the spec here

server/discover

• server/discover is answered without a session or handshake
  expected 200, got 0: {"_raw":"server exited"}

  0 !== 200

• server/discover advertises the versions the server can serve
  Cannot read properties of undefined (reading 'supportedVersions')

• server/discover is a CacheableResult with usable cache hints
  Cannot read properties of undefined (reading 'ttlMs')

• server/discover reports server identity and capabilities
  Cannot read properties of undefined (reading 'capabilities')

• server/discover is stable across calls within its own TTL
  Cannot read properties of undefined (reading 'supportedVersions')

• server/discover advertises a revision this suite supports
  Cannot read properties of undefined (reading 'supportedVersions')

Version negotiation

• a request with no version at all is served on the default
  a version-less request must be served, got 0: {"_raw":"server exited"}

  0 !== 200

Official SDK interop

• a stock official-SDK client completes the handshake
  MCP error -32000: Connection closed
• the handshake settles on a revision inside the supported window
  initialize must return a protocolVersion, got undefined
• a stock official-SDK client can list tools
  MCP error -32000: Connection closed

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 (4)

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

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 "sh -c '[ -d agent-opfor ] || git clone https://github.com/KeyValueSoftwareSystems/agent-opfor && cd agent-opfor && npm install && npm run build --workspaces --if-present && node runners/mcp/dist/index.js'" --spec-version 2026-07-28

(on Apple Silicon / arm64 hosts, add --platform linux/amd64; the published image currently only ships an amd64 manifest but runs fine under emulation)

Without Docker (npx):

npx @hasmcp/mcp-spec-test@latest -c "sh -c '[ -d agent-opfor ] || git clone https://github.com/KeyValueSoftwareSystems/agent-opfor && cd agent-opfor && npm install && npm run build --workspaces --if-present && node runners/mcp/dist/index.js'" --spec-version 2026-07-28

You can see the offending stdout line directly with:

node runners/mcp/dist/index.js
# stdout prints: ◇ injected env (0) from .env // tip: ⌘ enable debugging { debug: true }

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This report was generated by an automated MCP conformance sweep across public MCP server repos. If this turns out to be a false positive specific to the test container/environment, or not applicable, feel free to close it — no offense taken.