# Process Debug Systematic

> Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes

- Skill: `bitranox/process-debug-systematic` (Agent Skill, multi-file: 13 files)
- Install (CLI): `npx skillmds@latest add bitranox/process-debug-systematic`
- Raw SKILL.md: https://api.skillmd.com/api/skills/bitranox/process-debug-systematic/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: bitranox (https://skillmd.com/u/bitranox)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/bitranox/process-debug-systematic

---


# Systematic Debugging

> Adapted from the superpowers plugin (MIT).

## 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 NO)

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:**

> Offload the bounded search here to a **`sonnet`** finder subagent (locate similar working code, read
> the reference implementation fully, return only the relevant slices) - it keeps large reference files
> out of your context. Keep hypothesis/root-cause reasoning in the main (`opus`) agent - this deep reasoning is
> capability-sensitive, so if the session is on a lesser tier offer switch-model-or-continue (the main
> agent cannot self-switch its model), or hand the root-cause step to a pinned `opus` subagent. Multiple
> independent failures -> `bitranox:process-agents-dispatching-parallel`. Tiers: "Concrete tiers" in
> `bitranox:process-agents-subagent-driven-development`.

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
   - **Run both arms from the SAME path.** Comparing an old version against a new one by copying
     one of them to a scratch directory moves a SECOND variable: a program that derives anything
     from `__file__` or the working directory behaves differently when relocated, so the
     difference you measure is the relocation rather than the change. The artifact of a relocated
     arm tends to be the more flattering result, which is what makes it survive review. Swap the
     versions IN PLACE (stash, checkout, or a symlink the program resolves identically) and keep
     every path the same across arms.

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

5. **Closed-Source Peer: Escalate to Disassembly After the Second Dead Hypothesis**

   **WHEN the system on the other side of the bug is a closed-source binary you cannot
   read (a proprietary driver, firmware, appliance, or vendor tool) and you are testing
   hypotheses about its behavior black-box:**

   - 1st hypothesis dies against measurement -> form a new one (the normal Phase 3 loop).
   - **2nd hypothesis also dies against measurement -> STOP. Do not form a third
     black-box guess.** Disassemble the peer instead: a disassembler (for example
     Ghidra) driven by its scripting/Python bridge, plus any public PDB or symbols the
     vendor ships.
   - Read the disassembly to learn the PROTOCOL or format needed for interoperability -
     never to copy the implementation. Reverse-engineering for interoperability is the
     sanctioned use here; lifting the vendor's code is not.
   - Cite an address and a symbol for the conclusion, not "it must be doing X".
   - A clean refutation of your hypothesis is an equally valid result - it closes the
     question as surely as a confirmation does, so don't discard the disassembly pass
     because it disproved you.

   **Why:** each black-box hypothesis costs a full build-deploy-measure cycle. The
   detail that decides the bug (a parser quirk, a field only read on the first record,
   a byte offset) can exist nowhere in any public spec, so no amount of further
   black-box experiment reaches it - only reading the code does.

### 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 `bitranox:process-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:** most "no root cause" verdicts are incomplete investigation. Before accepting one,
name the evidence that RULED OUT a code cause - the absence of a cause you found is not
the same as a cause you excluded.

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

## Real-World Impact

From debugging sessions. The direction is the claim; the sizes are unmeasured, so do not
quote them as figures:
- Systematic investigation reaches a fix sooner than trying candidate fixes, and reaches
  the right one more often.
- A fix aimed at a confirmed root cause rarely introduces a new bug. Candidate fixes
  routinely do, because each one changes code that was never shown to be at fault.