debug

A step-by-step method for finding and fixing software bugs by reproducing the problem, forming possible explanations, and testing them with evidence.

In plain words
What is it for?
Use it when investigating errors, unexpected behavior, broken features, or suspected race conditions.
Why use it?
It replaces random code changes with a process that narrows the problem until its underlying cause is found.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/ao92265/claude-code-playbook/debug
Any agent
npx skills add ao92265/claude-code-playbook --skill debug
Clone the repo
git clone --depth 1 https://github.com/ao92265/claude-code-playbook

Made for: Claude Code, Codex.

Per session 81 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 647 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00081 $0.00647
Opus 5 $0.00041 $0.00324
Sonnet 5 $0.00016 $0.00129
Haiku 4.5 $0.00008 $0.00065

Measured 2d ago against content hash ac2764c38600, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

debug scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/debug/SKILL.md · 68 lines

How it starts

The opening of the file, as written. The whole thing — 68 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Structured Debugging

Systematic debugging using the scientific method. No more random changes hoping something works.

Steps

  1. Reproduce the bug:

    • Get the exact error message, stack trace, or unexpected behavior
    • Find the minimal reproduction case
    • Confirm it's reproducible (not a flaky test or race condition)
    • If it can't be reproduced, gather more data before proceeding
  2. Form a hypothesis:

    • Based on the error and context, what's the most likely cause?
    • List 2-3 possible causes ranked by probability
    • State what you'd expect to see if each hypothesis is correct
  3. Test the hypothesis:

    • Add a targeted log, breakpoint, or assertion to test the top hypothesis
    • Run the reproduction case
    • Does the evidence support or refute the hypothesis?
  4. Narrow down:

    • If hypothesis is supported: zoom in on the specific code path
    • If hypothesis is refuted: move to the next hypothesis
    • Use binary search: add a check at the midpoint of the suspected code path
    • Each step should cut the problem space in half
  5. Identify the root cause:

    • Don't stop at the symptom — find why it's happening
    • Check: is this a data issue, logic error, race condition, or configuration problem?
    • Verify the root cause explains ALL observed symptoms
  6. Fix and verify:

    • Make the minimum change that fixes the root cause
    • Run the original reproduction case — does it pass?
    • Run the full test suite — did the fix introduce regressions?
    • Remove any debugging artifacts (extra logs, breakpoints)
  7. Prevent recurrence:

    • Add a test case that would have caught this bug
    • Consider: should this be in tasks/lessons.md?
    • Is there a class of similar bugs that should be checked?

Important

  • Don't change code randomly. Every change should test a specific hypothesis.
  • Don't fix symptoms. A null check at the crash site is a band-aid — find why it's null.
  • Keep notes. Write down hypotheses and results so you don't re-test the same thing.
  • Time-box. If you're stuck after 3 hypotheses, step back and reconsider assumptions.
  • Remove debug artifacts. No console.log, debugger statements, or commented-out code in the final commit.

Read the full file on GitHub · 68 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 68 lines · 81 tokens per session scan A ac2764c38600

Subscribe to this mod's changes

debug is a skill published in the GitHub repository ao92265/claude-code-playbook (10 stars, last pushed 15d ago), licensed MIT. It adds 81 tokens to every session and 647 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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