Gauntlet

- type confusion (string where a number is required, …)
- boundary (empty / 100k-char strings, i64::MAX, negatives, zero, huge floats)
- missing required fields, wrong-typed arguments, deep nesting
- run: mcp-fuzz run --stdio --sarif mcp.sarif --fail-on high -- node server.js
- uses: github/codeql-action/upload-sarif@v3

The README includes setup instructions such as mcp-fuzz run --stdio -- node my-server.js.

mcp-fuzz run --stdio --tool search --iterations 300 --fail-on high -- ./server

It connects, calls tools/list, and for every tool generates payloads driven by the schema:

- type confusion (string where a number is required, …)

- boundary (empty / 100k-char strings, i64::MAX, negatives, zero, huge floats)

- injection (path traversal, SQLi, command/template/format-string, prompt injection, CRLF, NUL bytes, RTL/zero-width Unicode) — sent purely as data, never executed

- missing required fields, wrong-typed arguments, deep nesting
Outcomes are classified: a dropped connection ⇒ crash (HIGH), a timeout ⇒ hang (HIGH), -32603 ⇒ internal-error (MEDIUM), success on schema-invalid input ⇒ accepted-invalid (LOW). A clean -32602 invalid params is treated as the server correctly validating — not a finding.
Runs are reproducible (--seed). After a crash the fuzzer respawns the server and continues; if the server can't be brought back, it records that once and stops cleanly, rather than blaming every later payload for the original crash.

Findings (worst first):
[HIGH ] crash search::server crashed on field 'query': null-byte
stderr tail:
thread 'main' panicked at 'invalid utf-8 ...'
[LOW ] accepted-invalid search::schema-invalid input accepted without error: missing required field 'query'
``

- mcp-armor — runtime defense sidecar: scans tool calls, verifies signed manifests, blocks known-bad CVEs
- mcp-gauntlet (this one) — pre-deploy mcp-fuzz (schema-aware fuzzer) + mcp-storm (load tester)
- mcp-covenant — contract & breaking-change detector (semver for your MCP interface)
- mcp-herald — static migration linter for the MCP 2026-07-28 spec
- mcp-passport — publish-readiness validator for the MCP Registry
- mcp-otel — W3C Trace Context → OpenTelemetry bridge
- mcp-cache-kit — leak-safe SEP-2549 caching (ttlMs + cacheScope`)
- skilldoctor — linter + security scanner for agent skill files