---
name: systematic-debugging
description: Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes
---

# Systematic Debugging

## Overview

Random fixes waste time and create new bugs. Quick patches mask underlying issues.

**Core principle:** ALWAYS find root cause before attempting fixes. Symptom fixes are failure.

**Violating the letter of this process is violating the spirit of debugging.**

## The Iron Law

```
NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST
```

If you haven't completed Phase 1, you cannot propose fixes.

## When to Use

Use for ANY technical issue:

- Test failures
- Bugs in production
- Unexpected behavior
- Performance problems
- Build failures
- Integration issues

**Use this ESPECIALLY when:**

- Under time pressure (emergencies make guessing tempting)
- "Just one quick fix" seems obvious
- You've already tried multiple fixes
- Previous fix didn't work
- You don't fully understand the issue

**Don't skip when:**

- Issue seems simple (simple bugs have root causes too)
- You're in a hurry (rushing guarantees rework)
- Manager wants it fixed NOW (systematic is faster than thrashing)

## The Four Phases

You MUST complete each phase before proceeding to the next.

### Phase 1: Root Cause Investigation

**BEFORE attempting ANY fix:**

1. **Read Error Messages Carefully**
    - Don't skip past errors or warnings
    - They often contain the exact solution
    - Read stack traces completely
    - Note line numbers, file paths, error codes

2. **Reproduce Consistently**
    - Can you trigger it reliably?
    - What are the exact steps?
    - Does it happen every time?
    - If not reproducible → gather more data, don't guess

3. **Check Recent Changes**
    - What changed that could cause this?
    - Git diff, recent commits
    - New dependencies, config changes
    - Environmental differences

4. **Gather Evidence in Multi-Component Systems**

   **WHEN system has multiple components (CI → build → signing, API → service → database):**

   **BEFORE proposing fixes, add diagnostic instrumentation:**
   ```
   For EACH component boundary:
     - Log what data enters component
     - Log what data exits component
     - Verify environment/config propagation
     - Check state at each layer

   Run once to gather evidence showing WHERE it breaks
   THEN analyze evidence to identify failing component
   THEN investigate that specific component
   ```

   **Example (multi-layer system):**
   ```bash
   # Layer 1: Workflow
   echo "=== Secrets available in workflow: ==="
   echo "IDENTITY: ${IDENTITY:+SET}${IDENTITY:-UNSET}"

   # Layer 2: Build script
   echo "=== Env vars in build script: ==="
   env | grep IDENTITY || echo "IDENTITY not in environment"

   # Layer 3: Signing script
   echo "=== Keychain state: ==="
   security list-keychains
   security find-identity -v

   # Layer 4: Actual signing
   codesign --sign "$IDENTITY" --verbose=4 "$APP"
   ```

   **This reveals:** Which layer fails (secrets → workflow ✓, workflow → build ✗)

5. **Trace Data Flow**

   **WHEN error is deep in call stack:**

   See `root-cause-tracing.md` in this directory for the complete backward tracing technique.

   **Quick version:**
    - Where does bad value originate?
    - What called this with bad value?
    - Keep tracing up until you find the source
    - Fix at source, not at symptom

### Phase 2: Pattern Analysis

**Find the pattern before fixing:**

1. **Find Working Examples**
    - Locate similar working code in same codebase
    - What works that's similar to what's broken?

2. **Compare Against References**
    - If implementing pattern, read reference implementation COMPLETELY
    - Don't skim - read every line
    - Understand the pattern fully before applying

3. **Identify Differences**
    - What's different between working and broken?
    - List every difference, however small
    - Don't assume "that can't matter"

4. **Understand Dependencies**
    - What other components does this need?
    - What settings, config, environment?
    - What assumptions does it make?

### Phase 3: Hypothesis and Testing

**Scientific method:**

1. **Form Single Hypothesis**
    - State clearly: "I think X is the root cause because Y"
    - Write it down
    - Be specific, not vague

2. **Test Minimally**
    - Make the SMALLEST possible change to test hypothesis
    - One variable at a time
    - Don't fix multiple things at once

3. **Verify Before Continuing**
    - Did it work? Yes → Phase 4
    - Didn't work? Form NEW hypothesis
    - DON'T add more fixes on top

4. **When You Don't Know**
    - Say "I don't understand X"
    - Don't pretend to know
    - Ask for help
    - Research more

### Phase 4: Implementation

**Fix the root cause, not the symptom:**

1. **Create Failing Test Case**
    - Simplest possible reproduction
    - Automated test if possible
    - One-off test script if no framework
    - MUST have before fixing
    - Use the `superpowers:test-driven-development` skill for writing proper failing tests

2. **Implement Single Fix**
    - Address the root cause identified
    - ONE change at a time
    - No "while I'm here" improvements
    - No bundled refactoring

3. **Verify Fix**
    - Test passes now?
    - No other tests broken?
    - Issue actually resolved?

4. **If Fix Doesn't Work**
    - STOP
    - Count: How many fixes have you tried?
    - If < 3: Return to Phase 1, re-analyze with new information
    - **If ≥ 3: STOP and question the architecture (step 5 below)**
    - DON'T attempt Fix #4 without architectural discussion

5. **If 3+ Fixes Failed: Question Architecture**

   **Pattern indicating architectural problem:**
    - Each fix reveals new shared state/coupling/problem in different place
    - Fixes require "massive refactoring" to implement
    - Each fix creates new symptoms elsewhere

   **STOP and question fundamentals:**
    - Is this pattern fundamentally sound?
    - Are we "sticking with it through sheer inertia"?
    - Should we refactor architecture vs. continue fixing symptoms?

   **Discuss with your human partner before attempting more fixes**

   This is NOT a failed hypothesis - this is a wrong architecture.

## Red Flags - STOP and Follow Process

If you catch yourself thinking:

- "Quick fix for now, investigate later"
- "Just try changing X and see if it works"
- "Add multiple changes, run tests"
- "Skip the test, I'll manually verify"
- "It's probably X, let me fix that"
- "I don't fully understand but this might work"
- "Pattern says X but I'll adapt it differently"
- "Here are the main problems: [lists fixes without investigation]"
- Proposing solutions before tracing data flow
- **"One more fix attempt" (when already tried 2+)**
- **Each fix reveals new problem in different place**

**ALL of these mean: STOP. Return to Phase 1.**

**If 3+ fixes failed:** Question the architecture (see Phase 4.5)

## your human partner's Signals You're Doing It Wrong

**Watch for these redirections:**

- "Is that not happening?" - You assumed without verifying
- "Will it show us...?" - You should have added evidence gathering
- "Stop guessing" - You're proposing fixes without understanding
- "Ultrathink this" - Question fundamentals, not just symptoms
- "We're stuck?" (frustrated) - Your approach isn't working

**When you see these:** STOP. Return to Phase 1.

## Common Rationalizations

| Excuse                                       | Reality                                                                 |
|----------------------------------------------|-------------------------------------------------------------------------|
| "Issue is simple, don't need process"        | Simple issues have root causes too. Process is fast for simple bugs.    |
| "Emergency, no time for process"             | Systematic debugging is FASTER than guess-and-check thrashing.          |
| "Just try this first, then investigate"      | First fix sets the pattern. Do it right from the start.                 |
| "I'll write test after confirming fix works" | Untested fixes don't stick. Test first proves it.                       |
| "Multiple fixes at once saves time"          | Can't isolate what worked. Causes new bugs.                             |
| "Reference too long, I'll adapt the pattern" | Partial understanding guarantees bugs. Read it completely.              |
| "I see the problem, let me fix it"           | Seeing symptoms ≠ understanding root cause.                             |
| "One more fix attempt" (after 2+ failures)   | 3+ failures = architectural problem. Question pattern, don't fix again. |

## Quick Reference

| Phase                 | Key Activities                                         | Success Criteria            |
|-----------------------|--------------------------------------------------------|-----------------------------|
| **1. Root Cause**     | Read errors, reproduce, check changes, gather evidence | Understand WHAT and WHY     |
| **2. Pattern**        | Find working examples, compare                         | Identify differences        |
| **3. Hypothesis**     | Form theory, test minimally                            | Confirmed or new hypothesis |
| **4. Implementation** | Create test, fix, verify                               | Bug resolved, tests pass    |

## When Process Reveals "No Root Cause"

If systematic investigation reveals issue is truly environmental, timing-dependent, or external:

1. You've completed the process
2. Document what you investigated
3. Implement appropriate handling (retry, timeout, error message)
4. Add monitoring/logging for future investigation

**But:** 95% of "no root cause" cases are incomplete investigation.

## Supporting Techniques

These techniques are part of systematic debugging and available in this directory:

- **`root-cause-tracing.md`** - Trace bugs backward through call stack to find original trigger
- **`defense-in-depth.md`** - Add validation at multiple layers after finding root cause
- **`condition-based-waiting.md`** - Replace arbitrary timeouts with condition polling

**Related skills:**

- **superpowers:test-driven-development** - For creating failing test case (Phase 4, Step 1)
- **superpowers:verification-before-completion** - Verify fix worked before claiming success

## Real-World Impact

From debugging sessions:

- Systematic approach: 15-30 minutes to fix
- Random fixes approach: 2-3 hours of thrashing
- First-time fix rate: 95% vs 40%
- New bugs introduced: Near zero vs common
