ratemyagent

Test MCP servers like production services.

RateMyAgent is a reliability scanner for MCP servers. Most evaluation asks whether a tool can do the task. This asks whether it stays reliable when operated like a production service — under load, slow dependencies, rate limits, server errors, malformed replies and dropped connections.

Experimental / planned: an LLM adapter for Anthropic and OpenAI chat completions exists but has never been run against a live API (details), and an agent adapter is not started — see Roadmap.

NOTE: Read-only tools, STAGING rather than production: there's no dry-run yet. Expanding capabilities soon.

Point it at a target and it:

1. Measures a baseline — latency distribution, token cost, where concurrency saturates, and whether the tools enforce their own JSON Schema.
2. Injects faults — timeouts, 429s, 500s, malformed replies and refused connections, through a proxy the target cannot see.
3. Studies what happened — did each disrupted operation recover, and how many calls did it cost.

Then it scores the result 0–100 against a YAML policy you control, gates CI with an exit code, and writes an AGENTS.md fix guide you can hand straight to a coding agent.

It is built for the developer who wrote an MCP server — often with AI help — and wants to know whether it is ready before something depends on it. It tests behaviour, not source: a schema that is declared but never enforced, missing backpressure, or a retry loop that amplifies failures all show up in what the target does.

When the evidence cannot support a number, it says so instead of printing one. An unmeasurable check comes back n/a with the reason attached and leaves the score, rather than counting as a zero or a pass. Why that matters.

What it measures, and what it refuses to score

Five dimensions, weighted to 100. Each can decline.

The recovery threshold is derived, not fixed. The fault injector produces 1 - fault_rate ** retries against a target that never fails — 96% at the default rate — so a fixed floor would grade the flag rather than the target. Every report header states the rate and the floor it implies, because two scans at different rates are not comparable.

Targets: MCP over stdio, Streamable HTTP and SSE, plus five built-in mock profiles that need no server. The LLM adapter is experimental, as above. Outputs: terminal scorecard, markdown report, AGENTS.md, JSON. Every scan reproduces under --seed. Per-probe detail is in docs/PROBES.md.

Install

Published on PyPI. Python 3.10+.

pip install ratemyagent

That gives you the engine, the mock targets, and every output format — enough to run a full scan without installing anything else. The adapters that talk to real systems need their SDKs, which are optional so you only pull what you use:

pip install 'ratemyagent[mcp]'          # scan MCP servers (mcp SDK 1.x or 2.x)
pip install 'ratemyagent[anthropic]'    # scan Anthropic chat completions
pip install 'ratemyagent[openai]'       # scan OpenAI chat completions
pip install 'ratemyagent[all]'          # all of the above

With uv: uv tool install ratemyagent for a standalone CLI, or uv pip install 'ratemyagent[all]' into the current environment.

30 seconds, no API key

There is a built-in mock target, so you can see the whole thing work before pointing it at anything real. No key, no server, no network.

ratemyagent scan --target mock --profile degraded --requests 40 \
    --concurrency 16 --fault-rate 0.3

RateMyAgent Scan Results
========================

Target: degraded-mock (mock)
Probes: 6/6 complete   Duration: 0.01s
Faults: fault rate 30%, 2 retries -> recovery floor 91.0% (derived, not the policy value)

Phase 1  baseline
  Latency ................ p50 3.36s, p95 7.99s, p99 - over 40 requests (0.0% errors)
  Cost ................... 647 in / 120 out tokens per request, no price known for this model
  Concurrency ............ no saturation up to 16 concurrent, sustained 16
  Contract ............... 15 edge cases across 3 tools: 0 rejected cleanly, 15 accepted, 0 crashed

Phase 2  chaos (fault injection)
  Fault tolerance ........ 20 faults injected, 10/10 operations recovered (100%) within 2 retries, 1.30x call amplification

Phase 3  behavior analysis
  Behavior ............... 10/10 disrupted operations recovered (100%) within 2 retries, 1.30x amplification (ours), 0 duplicate deliveries (ours)

                             actual     target     status
  p95 latency                7.99s      5.00s      FAIL
  schema violations accepted 9          0          FAIL
  error rate                 0.0%       5.0%       pass ~
  contract crash rate        0.0%       0.0%       pass
  recovery rate              100.0%     91.0%      pass ~
  p99 latency                -          10.00s     n/a ~
  cost per request           -          $0.1000    n/a ~
  retry amplification        -          2.00x      n/a ~
  duplicate mutations        -          0          n/a ~

  ~ recovery rate -- 10/10 disrupted operations recovered, a
    95% interval of 72.2%-100.0%, which spans the 91.0% this
    fault rate produces against a target that never fails.
    recovery_rate_min is scored from it regardless. Remedy:
    --requests or --fault-rate.
  ~ error rate -- Zero failures in 40 requests bounds the
    error rate at roughly 8% with 95% confidence, not at 0%.
    Remedy: --requests.
  ~ 5 caveats on unscored rows (behavior, concurrency, cost,
    latency) -- -v to show.

  Score breakdown:
    latency         14/20     (p95 latency was 7,988ms, policy allows at most 5,000ms)
    cost            -/15      (not measured against this target)
    concurrency     -/15      (no policy threshold reads it)
    contract        8/15      (invalid inputs accepted was 9, policy allows at most 0)
    behavior        35/35

  Score: 81/100  (policy production-default)

Latency findings:
  - p95 7.99s and 0.0% errors across 40 requests, with no
    heavy tail, no unusual call overhead, and no error pattern
    to report.

Cost findings:
  - No cost problems found: 647 input tokens per request with
    no significant fixed prefix.

Concurrency findings:
  - Peak goodput is 4.4 successful req/s at 16 concurrent.
    Past that, added concurrency buys latency and errors
    rather than completed work.

Contract findings:
  - CRITICAL 9 inputs the schema forbids were accepted with a
    success response: missing_required[query],
    null_required[query], wrong_type[query]. Every accepted
    violation is on 'query'. The tool is not validating what
    it declares, so invalid data reaches whatever it writes
    to.

Fault tolerance findings:
  - Injected 20 faults across 93 calls (22%): 6 server_error,
    5 rate_limit, 4 connection_refused, 3 timeout, 2
    malformed.
  - Every one of the 10 disrupted operations recovered within
    2 retries.
  - Under fault the latency probe saw a 20% error rate, p95
    8.03s.

Behavior findings:
  - Every one of the 10 disrupted operations recovered within
    2 retries. That budget is the scanner's, not the target's,
    and is not configurable.

8 findings across 6 probes. Run with --output agents-md to generate a fix guide.

FAIL: score 81 meets pass threshold 75, but 2 checks failed: p95 latency, schema violations accepted.
Biggest gaps: contract (8/15), latency (14/20).

ratemyagent v1.4.1 - pip install ratemyagent - github.com/SMWundefined/RateMyAgent

How to read it:

• Actual sits next to target so the gap is the information.
• n/a means the probe could not measure this target. It is excluded from the score rather than counted as a failure.
• ~ marks a caveat about how strong the evidence is — here, that 10 disrupted operations cannot tell this target apart from the injector's own 91% floor.
• The last two lines are the verdict, because that is what a CI log gets searched for. A score above the pass threshold with a failed check is still a FAIL.

The target above is a built-in mock. Before reading a behavior row on a real MCP server the same way, see Known limitations.

Scan a real target

# An MCP server over stdio -- pass the tool and real arguments
ratemyagent scan --target mcp --uri "stdio://uvx mcp-server-git" \
    --tool git_log --tool-args '{"repo_path": "/path/to/repo"}'

# A hosted MCP server over Streamable HTTP
ratemyagent scan --target mcp --uri https://api.example.com/mcp \
    --header 'Authorization: Bearer $TOKEN'

Four things to know before scanning something real:

• Pass --tool and --tool-args. Probing calls a tool for real, once per request. Without real arguments, placeholders are synthesized from the schema, and if the server rejects them the scan refuses and exits 2 rather than scoring the rejection.
• Probing a write tool writes. Auto-selection only picks a tool it can establish is read-only; a tool that changes state needs --allow-mutating. Point that at something disposable.
• Credentials: --header for http/sse, --env KEY=VALUE for a stdio server — the MCP SDK does not pass your shell environment to the child process. Values are redacted in every report and export.
• A rate-limited dependency reads as an unreliable one. The scan becomes part of the load. Scale --requests to the quota.

Transports: https://host/mcp (Streamable HTTP), stdio://./server.py, and sse+https://host/sse (deprecated by the 2025-06-18 spec).

The detail behind each of these — the refusal messages, the read-only gate, credential redaction, --scan-timeout — is in docs/SCANNING.md.

Validated on two SQLite MCP servers. --verify-tool was run against npx mcp-sqlite@1.0.9 (create_record / read_records) and npx mcp-server-sqlite-npx@0.8.0 (write_query / read_query), each writing an {op_id} into a throwaway database. Both reported duplicate_mutations from the database's own contents — one operation applied twice on each, two on one arm — and a stdlib-only script that re-derives the ids and counts the rows agreed with every number. This is what a plain insert does under at-least-once retry: the reply was dropped after the row was written, the caller retried, and a second row appeared. Neither server is doing anything wrong, and neither finding is a bug report against them — an insert with no idempotency key behaves exactly this way, which is why it is the case worth being able to measure.

How a scan works

Three phases, in order. Phase 2 needs phase 1 to compare against; phase 3 reads what phase 2 recorded.

Phase 1 — Baseline. Latency, cost, concurrency and contract probes measure the target as it is. These are the numbers everything else is compared against.

Phase 2 — Fault injection. A FaultProxy wraps the target and injects faults at a configurable rate. Probes cannot tell they are wrapped, so the same probes run against a sabotaged target and any difference is attributable to the faults.

Phase 3 — Behavior analysis. Reads the trajectory of every operation phase 2 disrupted: did it recover, how long did that take, how many calls did one operation cost. This is the part that is not a load test — it measures behaviour under failure, not failure counts.

Against something that retries — an agent, or a client wrapping a service — the trajectory is the target's. Against a bare server the retry loop belongs to the scanner, so what gets scored there is target survivability.

The contributor-facing walkthrough is in docs/ARCHITECTURE.md.

Scoring

Results are scored 0–100 against a YAML policy. Probes measure; the policy decides.

• Meeting a threshold scores 100 for that check — a threshold is a limit, not a target.
• Missing it decays linearly to 0 at twice the limit, so a near miss and a catastrophe do not score alike.
• A metric the scan could not produce is skipped, not zeroed. Missing evidence is not a failure.
• Passing requires both a score at or above pass_score and no failed check. A failed check also caps the score at 89, or at 49 for a contract crash or a duplicate mutation, so one failure cannot be averaged away. A duplicate-mutation failure needs --verify-tool; without it the check is skipped rather than passed.

# my-policy.yaml
name: my-service
thresholds:
  p95_latency_ms: 3000
  error_rate_max: 0.02
  recovery_rate_min: 0.95
  retry_amplification_max: 1.5
  duplicate_mutation_max: 0
pass_score: 80

ratemyagent policy                                    # show the shipped defaults
ratemyagent scan --target mock --policy my-policy.yaml

Every threshold is optional, and an unknown key is an error rather than silently unscored. Full reference, including the shipped default explained threshold by threshold and how the caps work: docs/POLICY.md.

CI integration

ratemyagent ci --target mcp --uri stdio://./server.py --policy production.yaml
echo $?     # 0 pass, 1 fail, 2 the scan could not run

Exit code 2 matters: a broken scanner is not a failing target, and a gate that cannot tell them apart is not worth having in a pipeline. Failed checks are printed individually, and --scan-timeout bounds the whole run so a hung handshake fails cleanly instead of burning the job's time limit.

ci is the gate; scan is not. scan prints FAIL and still exits 0 — it reports, and a reporting command that exits non-zero breaks every pipeline that runs it for the artifact. Only ci turns the verdict into an exit code, so a gate that greps scan's output for FAIL is not a gate. Both exit 2 when the scan could not run at all, which since 1.4.1 includes a run refused because the target still holds the ids this seed would write, and a run whose --verify-tool was requested but did not measure.

# .github/workflows/reliability.yml
name: reliability

on: [push, pull_request]

jobs:
  scan:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: astral-sh/setup-uv@v5
        with:
          python-version: "3.12"

      - run: uv pip install --system '.[mcp]'

      - name: Reliability gate
        run: |
          ratemyagent ci \
            --target mcp --uri stdio://./server.py \
            --policy production.yaml \
            --requests 120 --concurrency 16 --fault-rate 0.25 \
            --json-out scan.json

      - uses: actions/upload-artifact@v4
        if: always()
        with:
          name: reliability-scan
          path: scan.json

Use enough requests that the numbers mean something. recovery_rate from the default 20 requests is measured over roughly 4 disrupted operations, which is an anecdote rather than a rate.

AGENTS.md and the report

ratemyagent scan --target mcp --uri stdio://./server.py --output all
# then, in Claude Code, Codex, Cursor or whatever you use:
#   "Read AGENTS.md and fix what it found."

Both markdown outputs are written to be handed straight to a coding agent. AGENTS.md is the fix guide — findings with root causes and copy-pasteable patches. REPORT.md is the evidence behind them — every metric, every probe, and how the scan was run, organized by phase. Hand over the first to get work done, the second when you want the model to check the reasoning rather than trust it. They are about 2,300 and 1,700 tokens, so both fit in any context window.

Each finding states what was observed, why it matters in production, the root cause — weighted toward what AI-generated servers actually get wrong — and a fix naming the tool that failed:

FINDING: 9 schema-forbidden inputs accepted

Your tool declares required fields and types in its JSON Schema but does not enforce them at runtime. This is common in AI-generated MCP servers where the schema is correct but the handler trusts its input. Every field marked "required" needs an explicit check before the handler touches the data, because the calling agent WILL send malformed arguments — that is normal traffic, not an attack.

Suggested fix for tool "search_database":

if "query" not in args or not isinstance(args["query"], str):
    return {"error": "query is required and must be a string"}

Re-scanning into the same file reports what changed since the last scan. Real output is in examples/: a scan of the official mcp-server-git (AGENTS.md, report) and a deliberately broken mock that triggers every finding at once.

Known limitations

Each of these affects scores you can produce today. The full account, with the measurements behind each one, is in docs/LIMITATIONS.md — read it before relying on a number.

• Retry behaviour is not scored against a bare MCP server. A server does not retry; the scanner does, so retry amplification describes RateMyAgent. It is reported, marked n/a, and becomes scoreable with an AgentTarget.
• Duplicate mutations need --verify-tool. Left to itself the scan counts calls it re-sent after dropping a reply and reports that as its own; it cannot see whether the target applied them twice. Pass a read-only tool that reports the target's state, with {op_id} in --tool-args, and the metric is measured per operation (how). Without it the check is skipped, not passed — and since 1.4.1 a scan whose oracle was requested but did not measure never prints PASS, and ci exits 2.
• Synthesized arguments are shallow. A scan refuses when the server rejects them, but a tool that accepts a placeholder is profiled on a trivial call.
• Network-backed targets vary run to run. Quote a range from repeated runs, with the count.
• The scan can cause the failure it reports. Against a rate limiter, retries add load. Since 1.0.1 the scan backs off and honours Retry-After, but it does not detect a quota.
• A latency figure describes the path the call took. A cache hit is a real cost, not a round trip to the dependency the tool's name implies.
• Faults are transient. Each attempt is faulted independently; sustained outages are not modelled.

API stability

1.0 means the frozen surface will not break without a major version. It does not mean the findings are finished — the section above says plainly what this tool still cannot measure.

Frozen: scan(), the target adapters, ProbeConfig, Policy, the result shapes (ScanResult, ProbeResult, CheckResult, Caveat), ErrorKind and FaultKind members, the CLI flags, the exit codes, and the eleven metric names a policy threshold reads.

Not frozen: the rest of ProbeResult.metrics, Response.meta, and ProbeConfig.extra keys with no CLI flag behind them. Each is a reporting channel rather than a contract, and anything a consumer comes to depend on gets promoted to a named field by a written procedure rather than by habit.

docs/API-STABILITY.md is the full statement, including the promotion rules and why each unfrozen thing is unfrozen. It ships in the sdist. Wheels carry no docs directory, so from a wheel this section and the file at the matching git tag are the reference.

Roadmap

• Next — ratemyagent chaos for targeted single-fault scenarios; --contract-tools to raise contract coverage above the default three (with a hazard noted in docs/SCANNING.md); a dry-run mode, which needs --verify-tool as its evidence that nothing was applied
• v2 — sustained outage windows; historical trending across scans; AgentTarget wrapping a Python script, gated on verify-tool catching a real applied duplicate on a real server (not yet: server-memory was a negative control) and on three outside users

Deliberately out of scope: web dashboards, continuous monitoring, framework-specific adapters, security scanning, and anything requiring a database.

Contributing

git clone https://github.com/SMWundefined/RateMyAgent.git
cd RateMyAgent

uv venv --python 3.12
uv pip install -e '.[dev]'              # editable, with pytest and ruff

uv run pytest -q                        # prints the count; no network or API keys
uv run ruff check .

Start with docs/ARCHITECTURE.md — it covers the Target interface, the FaultProxy, the trajectory model, and the policy engine, including the parts that are load-bearing and the reasoning behind them.

House rules, in short:

• Every probe needs tests that run without API keys, a network, or an MCP server. Use the mock targets in tests/conftest.py.
• Probes measure, the policy judges. A probe that emits a verdict is a bug.
• The FaultProxy is the only place faults are injected.
• No interactive prompts. This is an SRE tool; it has to stay pipeable.
• Say what you measured, not what you would like to be true. Findings call out thin evidence rather than letting it pass quietly.

License

Apache License 2.0 — see LICENSE and NOTICE.

Apache rather than MIT because it carries an express patent grant from contributors, and section 5 states that contributions are offered under the same terms unless you say otherwise. MIT is silent on both. Equally permissive; less for a legal review to work out.