$ ~/registry/skill/obra-debugging-root-cause-tracing

SKILL

Root Cause Tracing

Name: Root Cause Tracing
Author: obra

Trace bugs backward through call stacks to find the original trigger.

Stars

★ 40

Source

GitHub

Updated

2026-07-05

// securityLow risk

Prompt only, no code
Open source

Running security audit…

Credentials
Network egress
Code execution
Data access
Supply chain

// install

Copy the install command and let the AI configure it · recommended for beginners

Please install the "Root Cause Tracing" skill from askskill:
1. Download https://raw.githubusercontent.com/obra/clank/main/skills/debugging/root-cause-tracing/SKILL.md
2. Save it as ~/.claude/skills/root-cause-tracing/SKILL.md
3. Reload skills and tell me it's ready

// download

Download SKILL.mdInstall manifest ↗

// examples

Find the source of an API null pointer

Prompt

Using this stack trace and relevant code, trace the null pointer exception backward through the call chain. Show each function's inputs, outputs, and suspicious variables, then provide the most likely root cause and fix suggestion.

Expected

A step-by-step root cause analysis identifying the earliest failure point and a fix approach.

Investigate a failed async job

Prompt

Here are the failed async job logs, scheduling flow, and related service calls. Starting from the error point, trace backward to determine which upstream parameter, state change, or retry logic first caused the failure, and summarize it as an investigation report.

Expected

A report showing the failure propagation path, original trigger, and affected chain.

Analyze a production regression bug

Prompt

I have a production regression: after a new release, a feature returns incorrect results. Use the commit history, call stack, and observed test behavior to trace the root cause backward, identify the most likely change that introduced it, and provide verification steps.

Expected

A regression analysis with the suspected change, root cause judgment, and verification plan.

// docs

Root Cause Tracing

Overview

Bugs often manifest deep in the call stack (git init in wrong directory, file created in wrong location, database opened with wrong path). Your instinct is to fix where the error appears, but that's treating a symptom.

Core principle: Trace backward through the call chain until you find the original trigger, then fix at the source.

When to Use

digraph when_to_use {
    "Bug appears deep in stack?" [shape=diamond];
    "Can trace backwards?" [shape=diamond];
    "Fix at symptom point" [shape=box];
    "Trace to original trigger" [shape=box];
    "BETTER: Also add defense-in-depth" [shape=box];

    "Bug appears deep in stack?" -> "Can trace backwards?" [label="yes"];
    "Can trace backwards?" -> "Trace to original trigger" [label="yes"];
    "Can trace backwards?" -> "Fix at symptom point" [label="no - dead end"];
    "Trace to original trigger" -> "BETTER: Also add defense-in-depth";
}

Use when:

Error happens deep in execution (not at entry point)
Stack trace shows long call chain
Unclear where invalid data originated
Need to find which test/code triggers the problem

The Tracing Process

1. Observe the Symptom

Error: git init failed in /Users/jesse/project/packages/core

2. Find Immediate Cause

What code directly causes this?

await execFileAsync('git', ['init'], { cwd: projectDir });

3. Ask: What Called This?

WorktreeManager.createSessionWorktree(projectDir, sessionId)
  → called by Session.initializeWorkspace()
  → called by Session.create()
  → called by test at Project.create()

4. Keep Tracing Up

What value was passed?

projectDir = '' (empty string!)
Empty string as cwd resolves to process.cwd()
That's the source code directory!

5. Find Original Trigger

Where did empty string come from?

const context = setupCoreTest(); // Returns { tempDir: '' }
Project.create('name', context.tempDir); // Accessed before beforeEach!

Adding Stack Traces

When you can't trace manually, add instrumentation:

// Before the problematic operation
async function gitInit(directory: string) {
  const stack = new Error().stack;
  console.error('DEBUG git init:', {
    directory,
    cwd: process.cwd(),
    nodeEnv: process.env.NODE_ENV,
    stack,
  });

  await execFileAsync('git', ['init'], { cwd: directory });
}

Critical: Use console.error() in tests (not logger - may not show)

Run and capture:

npm test 2>&1 | grep 'DEBUG git init'

Analyze stack traces:

Look for test file names
Find the line number triggering the call
Identify the pattern (same test? same parameter?)

Finding Which Test Causes Pollution

If something appears during tests but you don't know which test:

Use the bisection script: @find-polluter.sh

./find-polluter.sh '.git' 'src/**/*.test.ts'

Runs tests one-by-one, stops at first polluter. See script for usage.

Real Example: Empty projectDir

Symptom: .git created in packages/core/ (source code)

Trace chain:

git init runs in process.cwd() ← empty cwd parameter
WorktreeManager called with empty projectDir
Session.create() passed empty string
Test accessed context.tempDir before beforeEach
setupCoreTest() returns { tempDir: '' } initially

Root cause: Top-level variable initialization accessing empty value

Fix: Made tempDir a getter that throws if accessed before beforeEach

Also added defense-in-depth:

Layer 1: Project.create() validates directory
Layer 2: WorkspaceManager validates not empty
Layer 3: NODE_ENV guard refuses git init outside tmpdir
Layer 4: Stack trace logging before git init

Key Principle

digraph principle {
    "Found immediate cause" [shape=ellipse];
    "Can trace one level up?" [shape=diamond];
    "Trace backwards" [shape=box];
    "Is this the source?" [shape=diamond];

…

View full docs ↗