debugging

A step-by-step method for finding the real cause of software bugs, from reproducing the problem to testing the fix.

In plain words
What is it for?
Use it to investigate failing tests, production errors, unexpected behavior, and bugs that have survived two or more attempted fixes.
Why use it?
It replaces random changes with evidence-based investigation when failures are unclear, unpredictable, or resistant to earlier fixes.

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/fakoli/fakoli-plugins/debugging
Any agent
npx skills add fakoli/fakoli-plugins --skill debugging
Clone the repo
git clone --depth 1 https://github.com/fakoli/fakoli-plugins

Made for: Claude Code, Codex.

Per session 102 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 738 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 $0.00102 $0.00738
Opus 5 $0.00051 $0.00369
Sonnet 5 $0.00020 $0.00148
Haiku 4.5 $0.00010 $0.00074

Measured yesterday against content hash 0c0d298075db, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

debugging 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 yesterday.

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.

plugins/fakoli-crew/skills/debugging/SKILL.md · 73 lines

How it starts

The opening of the file, as written. The whole thing — 73 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Systematic Debugging

A structured approach to debugging that prevents "try random fixes until something works."

When to Use

Activate this skill when any of the following hold:

  • A test is failing without an obvious cause.
  • A runtime error appears in production.
  • A bug report describes unexpected behavior whose source is unclear.
  • Two or more fix attempts have already failed.

The 4 Phases

Phase 1: Root Cause Investigation

  1. Read the error message completely — every line
  2. Reproduce the failure consistently
  3. Check recent changes: git diff HEAD~5 and git log --oneline -10
  4. Trace data flow backward from the symptom to the source
  5. Gather evidence: which inputs trigger the bug? Which don't?

Phase 2: Pattern Analysis

  1. Find a working example of similar code in the codebase
  2. Compare the broken path against the working path — line by line
  3. Identify every difference, not just the obvious one
  4. Check: does the working example handle an edge case the broken code doesn't?

Phase 3: Hypothesis & Test

  1. Form a single, specific hypothesis: "X fails because Y does Z when W"
  2. Design a minimal test that confirms or disproves the hypothesis
  3. Run the test
  4. If disproved → return to Phase 1 with new information
  5. If confirmed → proceed to Phase 4

Phase 4: Implementation

  1. Write a failing test that reproduces the exact bug
  2. Implement the single, minimal fix
  3. Run the failing test → should now pass
  4. Run ALL tests → should still pass
  5. If new failures appear → the fix is wrong, return to Phase 3

Red Flags (Violations)

Stop immediately if you catch yourself:

  • "Let me just try changing X" (no hypothesis)
  • Making multiple changes at once (untestable)
  • "This fix should work" without running the test
  • Fixing a different bug than the one reported
  • Deleting or modifying a test to make it pass

Escalation

If 3+ fix attempts have failed:

  1. Stop fixing
  2. Question the architecture — the bug may be a design problem
  3. Write up what you've learned and escalate to the orchestrator
  4. Include: what you tried, what happened, what you now suspect

Read the full file on GitHub · 73 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. yesterday First seen · 73 lines · 102 tokens per session scan A 0c0d298075db

Subscribe to this mod's changes

debugging is a skill published in the GitHub repository fakoli/fakoli-plugins (4 stars, last pushed 23d ago), licensed MIT. It adds 102 tokens to every session and 738 once invoked, about $0.0005 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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