FailTrace

Name: FailTrace
Author: LBarimi

by LBarimiversion 1.5.0i★ –iRuns on your computer

Registry nameio.github.LBarimi/failtrace

Install

Overview

Description from the maker (original English)

Debugging experiments for coding agents: reproduce failures and verify fixes with test evidence.

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: Developer tools

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).
The registry lists no key to fill in.

You need

npmNode.js installed (for the npx command)

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": {
    "failtrace": {
      "command": "npx",
      "args": [
        "-y",
        "failtrace",
        "mcp",
        "--cwd",
        "your-value"
      ]
    }
  }
}

Run this in your terminal

claude mcp add failtrace -- npx -y failtrace mcp --cwd your-value

This one needs values on its command line, so copy the settings and fill them in.

Or copy the settings yourself

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

{
  "mcpServers": {
    "failtrace": {
      "command": "npx",
      "args": [
        "-y",
        "failtrace",
        "mcp",
        "--cwd",
        "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 needs values on its command line, so copy the settings and fill them in.

Or copy the settings yourself

Paste into .vscode/mcp.json in your project

{
  "servers": {
    "failtrace": {
      "type": "stdio",
      "command": "npx",
      "args": [
        "-y",
        "failtrace",
        "mcp",
        "--cwd",
        "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.

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 6, 2026

✓ Pass
Maker matches the repo
The registry name was verified with the GitHub account LBarimi, 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 Developer toolsi

More stars than 0% of the other 1387 servers in this category
Published to the registry more recently than 49% of the other 1387 servers in this category
Basic checks equal to or better than 100% of the other 1387 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 FailTrace 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 (1.5.0) reached the registry 2 months ago.

Which apps can use it?

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

What can I use instead?

In the same category: GitHub, Desktop Commander, Cloudflare MCP

Alternatives

Servers in the same category from other makers, sorted by stars.

Reading a card:★ GitHub starsiThree pillars: reviews · checks · usageiUpdated = latest version published to the registryi

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Install

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.

FailTrace

Reproduce the failure. Check the fix.

A test fails intermittently. Your coding agent changes the code. One passing retry leaves you guessing.

FailTrace repeats the same check, saves a failing baseline, and checks the proposed fix against it. Use the CLI or MCP tools to get trial results, a smaller reproducer, and evidence your agent can inspect before accepting a patch.

Local execution. No AI API, account, or telemetry required. Keep your existing test runner and assertions.

Quick start

With Node.js 22.12+ and npm, run this in any working directory:

npx --yes failtrace demo

Static walkthrough · Static poster · Demo guide

The demo reduces six input items to ["BUG"], rejects a patch that crashes for another reason, and checks a working patch. It saves the evidence in .failtrace/ and prints a replay command.

For coding agents

Connect the local stdio MCP server through your client's configuration:

npx --yes failtrace@1.5.0 mcp --cwd "/absolute/path/to/your/project"

[Copy the MCP configuration and check the connection →](docs/AGENT-WORKFLOWS.md#mcp-client-configuration-and-windows-paths)

Your client launches this command. Running it alone in a terminal waits for MCP requests. The guide includes Windows setup.

Then ask your agent:

Use FailTrace to capture this test failure before editing. Choose the exact test or failure message, save a bounded baseline, and inspect the matching trial. After the change, verify against that baseline and explain any unrelated errors or incomplete evidence.

The seven MCP tools share the CLI's Core engine. They retain the failure signature and investigation evidence across repetition, comparison, regression search, minimization, verification and replay. Agents can retrieve saved trial and log pages without rerunning the command. Shell-capable agents can also use the CLI with --json.

The agent can inspect the saved failure before checking the patch.

Recheck an existing unit test

Follow an exact NUnit or Unity test through a fix. Each attempt gets a fresh NUnit 3 report. Missing or skipped tests and unrelated failures stay inconclusive, so an agent cannot accept them as evidence that the selected test passed.

Connect your test or try the original EditMode example →

NUnit support is included in 1.3.0 through CLI and MCP. The documented Unity validation covers the Windows EditMode example.

The selected test stays the same; a skipped report is not accepted as a passing test.

Use it on your own failure

From your project, replace the command and message with your own:

npx --yes failtrace@1.5.0 run "npm test -- checkout" --repeat 20 --stderr-contains "checkout failed" --capture-context

Run this before editing in a Git project. --capture-context records source identity for Verify; outside Git, select files with --context-source. Each trial saves its output, and exit 1 can mean the target was captured successfully. Then edit and verify the patch →

Your next question	Command
How often does this failure appear?	`run`
What differs between a healthy and failing trial?	`compare`
Which Git change introduced it?	`bisect`
What input is enough to reproduce it?	`minimize`
What happened after the proposed fix?	`verify`
How can I replay this investigation?	`bundle`

Command reference · Literal executable arguments · Reusable project scripts

The demo's bundle reproduces its original failure with exit 1. Keep the source, input and replay together; supply the target's prerequisites when packaging your own investigation.

What the results establish

FailTrace reports observations under the chosen settings. Verify separates a target observed, a healthy sample without that target, and inconclusive evidence. Bisect reports a sampled first-parent boundary; minimization rechecks its result without promising the smallest possible input.

The demo shows controlled example outcomes, not performance measurements. A passing sample does not prove a bug is gone.

Commands run with your permissions, and process cleanup is best effort. Retained stdout/stderr is capped by default at 16 MiB per trial and 256 MiB per run or bisect/minimization. Previous investigations accumulate separately. Review logs, commands and selected files before sharing; bundles still require the target's dependencies and setup.

Result and exit-code reference · Resource limits · Storage inventory · Bundle guide

Availability and contributing

The quick start uses npm's latest release; the verified version is 1.5.0. MCP configuration and repeatable installation examples keep that exact version pinned: installation options, GitHub release, and MCP Registry entry.

Version 1.5.0 adds: short run references, Verify readiness and next-step guidance, and intermittent-minimization guidance. See the changelog.

[Documentation: choose your next task →](docs/README.md)

Development instructions · Compatibility · Roadmap · Third-party notices

FailTrace

Overview

PopNx MCP’s three pillars

What you can do with it

Install

Before you install

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 Developer toolsi

Common questions

Alternatives

GitHub

Desktop Commander

Cloudflare MCP

README from the maker

FailTrace

Quick start

For coding agents

Recheck an existing unit test

Use it on your own failure

What the results establish

Availability and contributing