MCP Failure Lab

Name: MCP Failure Lab
Author: cloudlabworks

by cloudlabworksversion 0.1.2i★ –iRuns on your computer

Registry nameio.github.cloudlabworks/mcp-failure-lab

Install

Overview

Description from the maker (original English)

Deliberately faulty MCP server for testing how agent clients handle tool errors and disconnects.

PopNx MCP’s three pillars

These three are never merged into one score: opinions, measurements and popularity are different things.

User voiceiNo reviews yetReviews open together with accounts in a later step
Our basic checksi1 of 1 passedChecked from public information; code not scanned yet
UsageiNot measured yet★ –

What you can do with it

We have not written a plain-language summary for this one yet. Below are the facts we read from the registry.

Connection: Runs on your computer
Transport: stdio
Category: Other

Install

Pick the AI app you use, then copy the settings.

Before you install

Basic checks: 1 of 1 passed
Runs on your computer with your user’s permissions (files, network, apps).
You fill in yourself: LAB_SCENARIO, LAB_DELAY_MS, LAB_FAILURES

You need

DockerDocker installed

Which app do you use?

ClaudeClaude CodeCursorVS CodeChatGPT

Pick your app above. We remember it, so next time the button says “Install in …”.

Open Claude Desktop → Settings → Developer → Edit Config, and paste this into claude_desktop_config.json

{
  "mcpServers": {
    "failure-lab": {
      "command": "docker",
      "args": [
        "run",
        "-i",
        "--rm",
        "-e",
        "LAB_SCENARIO",
        "-e",
        "LAB_DELAY_MS",
        "-e",
        "LAB_FAILURES",
        "ghcr.io/cloudlabworks/mcp-failure-lab:0.1.2"
      ],
      "env": {
        "LAB_SCENARIO": "your-value",
        "LAB_DELAY_MS": "your-value",
        "LAB_FAILURES": "your-value"
      }
    }
  }
}

Run this in your terminal

claude mcp add failure-lab --env LAB_SCENARIO=your-value --env LAB_DELAY_MS=your-value --env LAB_FAILURES=your-value -- docker run -i --rm -e LAB_SCENARIO -e LAB_DELAY_MS -e LAB_FAILURES ghcr.io/cloudlabworks/mcp-failure-lab:0.1.2

Fill in the empty values before running it.

Open in Cursor

Or copy the settings yourself

Paste into .cursor/mcp.json in your project, or ~/.cursor/mcp.json

{
  "mcpServers": {
    "failure-lab": {
      "command": "docker",
      "args": [
        "run",
        "-i",
        "--rm",
        "-e",
        "LAB_SCENARIO",
        "-e",
        "LAB_DELAY_MS",
        "-e",
        "LAB_FAILURES",
        "ghcr.io/cloudlabworks/mcp-failure-lab:0.1.2"
      ],
      "env": {
        "LAB_SCENARIO": "your-value",
        "LAB_DELAY_MS": "your-value",
        "LAB_FAILURES": "your-value"
      }
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

Open in VS Code

Or copy the settings yourself

Paste into .vscode/mcp.json in your project

{
  "servers": {
    "failure-lab": {
      "type": "stdio",
      "command": "docker",
      "args": [
        "run",
        "-i",
        "--rm",
        "-e",
        "LAB_SCENARIO",
        "-e",
        "LAB_DELAY_MS",
        "-e",
        "LAB_FAILURES",
        "ghcr.io/cloudlabworks/mcp-failure-lab:0.1.2"
      ],
      "env": {
        "LAB_SCENARIO": "your-value",
        "LAB_DELAY_MS": "your-value",
        "LAB_FAILURES": "your-value"
      }
    }
  }
}

Your browser asks to open the app, then the app shows the settings and asks you to confirm. Key values are left empty for you to fill in.

This one runs on your computer, and ChatGPT can only connect to servers on the internet. Pick another app.

Your choice stays on this device in a cookie; no account needed.

Values you fill in

LAB_SCENARIO env
Fault to inject: healthy, tool-error, transient-error, delay, malformed, or disconnect
LAB_DELAY_MS env
Delay in milliseconds for the delay scenario (0 to 10000)
LAB_FAILURES env
Failing calls before success for the transient-error scenario (0 to 10)

These settings are generated from the maker’s registry entry. If the README says otherwise, follow the README.

What it can do

Runs on your computer; the tool list appears in your AI app after you install it.

Basic checksi

We check information anyone can see; we have not read the code. Checks that do not apply are left out of the count. · Checked Nov 7, 2026

✓ Pass
Maker matches the repo
The registry name was verified with the GitHub account cloudlabworks, which owns the repo
… Not checked yet
Still maintained
We have not read this repo from GitHub yet
… Not checked yet
Has a licence
We have not read this repo from GitHub yet
– Not applicable
Endpoint responds
This one runs on your computer; there is no internet endpoint
– Not applicable
Sign-in with OAuth
Runs on your computer and uses local settings instead
… Not checked yet
No hidden instructions in tool descriptions
Runs on your computer; we can only read tool lists from internet endpoints

Compared with others in Otheri

More stars than 0% of the other 32623 servers in this category
Published to the registry more recently than 89% of the other 32623 servers in this category
Basic checks equal to or better than 100% of the other 32623 servers in this category

Compared with every active server in this category in the registry. Stars count only when the publisher owns the repo.

Common questions

Is MCP Failure Lab safe?

It passed 1 of 1 applicable basic checks. We have not read the code. Before adding a key or token, see what access the server asks for and use a key with only the permissions you need.

What keys or codes does it need?

The registry does not list a required key, though some servers ask you to sign in on first use.

Does it run on my computer or in the cloud?

It runs on your computer. Your AI app starts it when needed, and data does not pass through the maker’s servers (unless it calls an online service itself).

Is it still maintained?

The GitHub repo last changed –, and the latest version (0.1.2) reached the registry 4 days ago.

Which apps can use it?

Apps that support MCP, such as Claude Desktop, Claude Code, Cursor and VS Code. You also need Docker on your computer.

What can I use instead?

In the same category: Spec Driven Development, Remote Desktop Commander, Draugr

Alternatives

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README from the maker

Open the README

Copied from the maker’s repo as written. PopNx MCP has not reviewed or endorsed it. HTML, images and scripts are removed. Links lead off this site.

MCP Failure Lab

A deliberately faulty MCP server and a bounded reference-client harness. v0.1.0, MIT. Built on the official MCP TypeScript SDK 2.3.1, not a replacement protocol implementation.

Try it

Requires Docker. The image uses Node 24 and pinned npm dependencies.

docker build -t mcp-failure-lab:local .

docker run --rm --network none --read-only --cap-drop ALL --security-opt no-new-privileges mcp-failure-lab:local npm test docker run --rm --network none --read-only --cap-drop ALL --security-opt no-new-privileges mcp-failure-lab:local node runner.mjs

The last command prints JSON results and OpenAI-message-shaped traces from seven deterministic runs. No language model participates. Timings are observed elapsed milliseconds, not benchmarks. The test command exits nonzero on a regression; the demo command emits observations, not a grading verdict.

For local development: npm ci --ignore-scripts, then npm test.

From the published image (Official MCP Registry: io.github.cloudlabworks/mcp-failure-lab):

docker run -i --rm -e LAB_SCENARIO=tool-error ghcr.io/cloudlabworks/mcp-failure-lab:0.1.2

Verifying a release

From v0.1.2, each release has build provenance signed through Sigstore by the publish-mcp workflow. With the GitHub CLI:

gh attestation verify oci://ghcr.io/cloudlabworks/mcp-failure-lab:0.1.2 --repo cloudlabworks/mcp-failure-lab

gh attestation verify mcp-failure-lab-0.1.2.tar.gz --repo cloudlabworks/mcp-failure-lab

The second command checks the source tarball from the GitHub Release. To verify offline, add --bundle mcp-failure-lab-0.1.2.tar.gz.intoto.jsonl (the provenance file attached to the same release).

Faults

LAB_SCENARIO	Injected behavior	Reference-client expectation
healthy	Normal tool response	One success
tool-error	Valid result with isError=true	Stop at configured attempt budget
transient-error	First LAB_FAILURES calls fail	Recover if the attempt budget permits
delay	Wait LAB_DELAY_MS before tool response	Succeed within deadline or time out
malformed	Valid JSON-RPC envelope, invalid text-block value	Reject the tool result
disconnect	Exit during a tool response	Report closed connection, not success

Only the advertised lab_probe tool is affected. Initialization and discovery use the official SDK. The transport wrapper corrupts result shape, not JSON framing; truncated frames, bad IDs, HTTP failures and authentication faults are not implemented.

Configuration is read at process startup. Scenarios reset per process. LAB_DELAY_MS: integer 0–10000 (default 1000). LAB_FAILURES: integer 0–10 (default 2). Values must be plain decimal digits; an unset or empty variable uses the default, and anything else (0x10, 1e3, 7) stops the server with exit code 2. The reference client retries only explicit tool errors, at most five attempts; protocol errors, timeouts and disconnects stop immediately. The harness's tool-call deadline is 10–10000 ms; SDK connection/discovery deadlines are separate. Retries intentionally have no backoff so the generated fixture exposes repeated calls; this is not recommended production retry policy.

Attach your own MCP client

Configure a test MCP connection to run this command, with stdin/stdout attached:

docker run --rm -i --network none --read-only --cap-drop ALL --security-opt no-new-privileges -e LAB_SCENARIO=transient-error -e LAB_FAILURES=2 mcp-failure-lab:local

Call lab_probe with {"message":"probe"}. There are no real downstream services, credentials, file-writing tools or listening network ports. Client integrations beyond the included reference client are unverified.

Feed a failure into Agent Trace Clinic

From this repository, with Clinic checked out next to it:

mkdir -p artifacts

docker run --rm --network none --read-only mcp-failure-lab:local node runner.mjs > artifacts/run.json node --input-type=module -e 'import fs from "node:fs"; const r=JSON.parse(fs.readFileSync("artifacts/run.json","utf8")); console.log(JSON.stringify(r.results.find(x=>x.scenario==="tool-error").trace));' > artifacts/tool-error.json node ../agent-trace-clinic/cli.mjs artifacts/tool-error.json --html > artifacts/clinic-report.html

Clinic should identify tool_loop, retry_storm and unhandled_tool_error on this fixture. These are heuristic leads: deliberate bounded retries can also trigger them. No token counts are invented.

Relationship to upstream

MCP conformance is the upstream authority for protocol tests. This project contributes a small fault surface for recovery experiments; it does not claim conformance certification. The official framework currently documents HTTP-based client/server scenario runners. This first release is stdio-only; an upstream scenario adapter and a Streamable HTTP target are next, not shipped capabilities.

Sources checked 2026-10-14:

Maintenance contract

One transport, one tool, six fault modes, one reference client. Pin SDK upgrades and rerun every fault test. Owner: Cloud Lab Works / Waku. Gherkin review has not been assigned or completed. Before public release: source/dependency review, an independent test pass, and publication approval. Before cloud execution: bounded job budget, teardown, and measured runtime. No cloud account is required for this release. No telemetry or remote reporting. Generated reports stay in ignored artifacts/.

Agent Reliability Lab

Open the public demo or read the experiment guide. Four controlled before/after cases connect the official MCP reference client to deterministic Clinic inspection. The public sample is recorded local evidence, not a live cloud execution. Cloud adapters and runbook are included.

Citation

If you use this project, please cite the accompanying preprint: MCP Failure Lab: Reproducible Tool-Failure Fixtures and Cross-Platform Traces for Testing Agent Reliability. DOI: 10.5281/zenodo.23720942. See the paper page for the abstract and PDF.

@techreport{alvord2026mcp,

author = {Alvord, Alex}, title = {{MCP Failure Lab: Reproducible Tool-Failure Fixtures and Cross-Platform Traces for Testing Agent Reliability}}, institution = {CloudLab Works}, publisher = {Zenodo}, year = {2026}, month = oct, type = {Preprint}, doi = {10.5281/zenodo.23720942}, url = {https://doi.org/10.5281/zenodo.23720942} }

MCP Failure Lab

Overview

PopNx MCP’s three pillars

What you can do with it

Install

Before you install

Values you fill in

What it can do

Basic checksi

Maker matches the repo

Still maintained

Has a licence

Endpoint responds

Sign-in with OAuth

No hidden instructions in tool descriptions

Compared with others in Otheri

Common questions

Alternatives

Spec Driven Development

Remote Desktop Commander

Draugr

README from the maker

MCP Failure Lab

Try it

Verifying a release

Faults

Attach your own MCP client

Feed a failure into Agent Trace Clinic

Relationship to upstream

Maintenance contract

Agent Reliability Lab

Citation