mcp-check-fixture

The MCP server MCPJam's GitHub PR checks are validated against. This directory is the seed for the standalone public repository mcpjam/mcp-check-fixture — the only repo the walking-skeleton check pipeline is wired to (server/services/github-checks/recipes.ts).

It lives here so it is reviewed alongside the pipeline that depends on it, and so the ops step is "copy and push" rather than "write from scratch".

Publishing it

cp -R test-servers/mcp-check-fixture /tmp/mcp-check-fixture
cd /tmp/mcp-check-fixture
git init && git add -A && git commit -m "mcp-check-fixture: minimal MCP server"
gh repo create mcpjam/mcp-check-fixture --public --source=. --push

package-lock.json is committed here on purpose, and must stay committed in the published repo: the run recipe uses npm ci, which fails outright without one. A repo missing its lockfile reports build_failed — correctly, but confusingly. @types/node is likewise a real devDependency, not an assumption about the build environment: tsconfig.json declares "types": ["node"], and this package is standalone with no workspace to hoist it from.

The two things that must not be "cleaned up"

It binds 0.0.0.0, not 127.0.0.1. E2B's host bridge only forwards to ports bound on all interfaces. A loopback-only server is invisible from outside the sandbox and the check reports server_unhealthy with a stderr tail that may not mention the bind address at all.

It answers initialize on /mcp immediately. That handshake is the health probe — the worker polls it until it succeeds. Anything that delays it (a warm-up, a lazily mounted route) reads as an unhealthy server.

Run recipe

The recipe hardcoded in the Inspector for this repo:

field	value
build	npm ci && npm run build
start	npm start
port	3001
mcpPath	/mcp

Changing any of those means changing recipes.ts in the same breath.

Tools

Three, all deterministic and side-effect-free — the eval suite's job is to prove the pipeline works, not to be an interesting test:

• echo({ text }) → the same text
• add({ a, b }) → the sum
• server_info() → {"name":"mcp-check-fixture","version":"1.0.0"}

Locally

npm install && npm run build && npm start
curl -s localhost:3001/mcp -H 'content-type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"curl","version":"1"}}}'

Exercising the check's failure modes

Each of these is a one-line change, and each should produce a specific check conclusion — useful for verifying the pipeline end to end:

Change	Expected outcome	Check conclusion
break a tool's return value	evals_failed	failure
introduce a type error	build_failed	failure
throw at the top of server.ts	server_unhealthy	failure
bind 127.0.0.1 instead of 0.0.0.0	server_unhealthy	failure