mcpprobe

Security scanner for Model Context Protocol servers. It checks authentication, OAuth metadata, transport conformance, tool-description poisoning, rug pulls, secrets in metadata, verbose errors and basic resource limits, maps every finding to the OWASP MCP, Agentic and LLM Top 10 lists, and writes JSON, SARIF 2.1.0 and a readable terminal summary.

It runs locally, sends no telemetry, and never calls a tool in its default mode.

Only scan servers you own or are explicitly authorised to test. See Ownership rule.

60-second quickstart

$ pipx run --spec mcpprobe-scanner mcpprobe https://your-server.example/mcp

or install it:

$ pipx install mcpprobe-scanner    # or: pip install mcpprobe-scanner; the command is `mcpprobe`
$ mcpprobe https://your-server.example/mcp --sarif mcpprobe.sarif --json mcpprobe.json

A local stdio server you run yourself:

$ mcpprobe --stdio "npx -y @your-scope/your-mcp-server@1.2.3"

Passing a bearer token you own (for checks behind your auth):

$ mcpprobe https://your-server.example/mcp --header "Authorization: Bearer $MCP_TEST_TOKEN"

The summary lists each finding with severity, check ID, confidence, OWASP mapping, an evidence excerpt and a plain-English fix, followed by a coverage table showing which checks ran, which were skipped and why. mcpprobe checks lists every check; CHECKS.md documents them in full.

What it checks

Protocol revisions: the scanner tries server/discover (2026-07-28) first, then initialize with 2025-11-25 and 2025-06-18, then the deprecated 2024-11-05 HTTP+SSE transport, and records which one answered.

Passive vs active

Passive (default) sends only what a normal MCP client sends (negotiation, the */list methods, well-known metadata documents) plus a handful of benign malformed requests (bad Origin, bogus version header, forged session ID, self-minted wrong-audience JWT, truncated JSON, one oversized and one deeply nested request). It never calls a tool.

Active (--active) is for checks that call tools with non-destructive canaries. In 0.1.0 these are stubs, but the gate is real and enforced in code. Active mode is refused unless you pass all of:

• --authorised-by "<who approved this, e.g. name/role/ticket>"
• --scope "<what is in scope>"
• --verify dns-txt (HTTP targets) or --verify local (stdio servers you run yourself)

For dns-txt, generate a token and publish it:

$ mcpprobe token your-server.example
Publish this DNS TXT record, then run with --active --verify dns-txt:
  _mcpprobe.your-server.example.  TXT  "mcpprobe-verification=<token>"
$ mcpprobe https://your-server.example/mcp --active --verify dns-txt \
    --authorised-by "platform security, CHG-1234" --scope "https://your-server.example/mcp" \
    --json scan.json

Every active run writes an authorisation record (scan.authorisation.json next to the report): who authorised it, the scope, the verification proof, rate cap and excluded tools. Use --exclude-tool NAME for tools that must never be called.

Ownership rule

Scan only MCP servers you own, operate, or have explicit written permission to test. This applies to passive mode too: even benign requests are unauthorised access if the system is not yours. mcpprobe identifies itself on every request and honours opt-outs (below), but those are courtesy mechanisms, not permission.

Scanner identification, opt-out and rate limits

• User-Agent: mcpprobe/<version> (+https://mcpprobe.tech/scanning-policy).
• Opt-out, checked before any MCP request and impossible to override:
  • DNS TXT mcpprobe-opt-out=all at _mcpprobe.<host> (or a parent domain), checked before any packet reaches the host;
  • an HTTP 200 at /.well-known/mcpprobe-opt-out.
• Rate: 5 requests/second by default (--rate), hard ceiling 10.

Exit codes

SARIF and GitHub code scanning

As a GitHub Action (Docker container action, no Python setup needed):

name: MCP security
on: [push, pull_request]
permissions:
  contents: read
  security-events: write
jobs:
  mcpprobe:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: mcpprobe-dev/mcpprobe@v0.1.0
        with:
          target: https://staging.your-server.example/mcp
          fail-on: high
          sarif-output: mcpprobe.sarif
          sarif-location: src/server.py   # optional: anchor alerts to a repo file
      - uses: github/codeql-action/upload-sarif@v3
        if: always()
        with:
          sarif_file: mcpprobe.sarif
          category: mcpprobe

Or from any CI with the CLI:

$ pipx run --spec mcpprobe-scanner mcpprobe https://staging.your-server.example/mcp --sarif mcpprobe.sarif --fail-on high

Results use error for critical/high, warning for medium and note for low/info, with GitHub's security-severity on each rule and the OWASP IDs as tags. Because a scanned endpoint is not a file, results point at the target URL unless you pass --sarif-location.

Rug-pull detection

$ mcpprobe https://your-server.example/mcp --baseline .mcpprobe/baseline.json

The first run stores canonical SHA-256 hashes of every tool, prompt, resource and the server instructions. Later runs report anything added, removed or changed (a changed description after approval is the classic rug pull) and update the file; use --no-write-baseline to compare without updating.

Reports and evidence

• --json FILE: the full report, including every request/response pair (timestamp, method, status, a header subset, bodies truncated to 4 KB). Authorization values and recognised secret patterns are redacted.
• --sarif FILE: SARIF 2.1.0.
• -v: descriptions and scan notes in the terminal; -q: no terminal output.

Server-supplied text is shown with control characters made visible and is never interpreted as terminal markup.

Python API and LLM-judge hook

import asyncio
from mcpprobe.checks import JudgeVerdict, ScanOptions
from mcpprobe.scanner import ScanConfig, run_scan


def judge(text: str, task: str) -> JudgeVerdict | None:
    return None  # plug in your own model here; mcpprobe makes no LLM calls


report, evidence = asyncio.run(
    run_scan(ScanConfig(target="https://your-server.example/mcp", options=ScanOptions(judge=judge)))
)
print(report.counts())

Development

$ pip install -e ".[dev]"
$ ruff check . && ruff format --check . && mypy && pytest
$ python -m tests.fake_server --preset vulnerable --port 8765   # deliberately vulnerable local server
$ mcpprobe http://127.0.0.1:8765/mcp

Security issues: see SECURITY.md. Licence: MIT.