fix-bug

A test-first process for fixing software bugs: reproduce the problem, find its cause, and then apply the fix. It applies when software behaves unexpectedly or a defect is reported.

In plain words
What is it for?
Use it to investigate broken behavior, write a reproduction test, identify the root cause, implement the correction, and verify nearby behavior.
Why use it?
It prevents fixes based only on guesswork by requiring a failing test and a diagnosis before changing the code.

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/nowsprinting/unity-coding-skills/fix-bug
Any agent
npx skills add nowsprinting/unity-coding-skills --skill fix-bug
Clone the repo
git clone --depth 1 https://github.com/nowsprinting/unity-coding-skills

Made for: Claude Code, Codex.

Per session 86 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,309 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 $0.00086 $0.02309
Opus 5 $0.00043 $0.01154
Sonnet 5 $0.00017 $0.00462
Haiku 4.5 $0.00009 $0.00231

Measured 2d ago against content hash 613d4f527918, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

fix-bug 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/fix-bug/SKILL.md · 177 lines

How it starts

The opening of the file, as written. The whole thing — 177 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Guide for diagnosing and fixing bugs. This skill defines a test-first debugging workflow: reproduce the bug with a failing test, diagnose the root cause, then fix it.

Mode Check

This skill must be used outside plan mode. Before doing anything else, check the current mode:

  • ExitPlanMode is NOT in the deferred tools list (i.e., directly callable) → in plan mode → stop immediately and tell the user:

    "This skill (/fix-bug) must be used outside plan mode. Please exit plan mode first."

  • ExitPlanMode is in the deferred tools list → not in plan mode → proceed.

Workflow

Recording implementation notes: Notes for this run go in /tmp/fix-bug-notes-$CLAUDE_CODE_SESSION_ID.md. Immediately before your first append in this run — and only then — delete that file if it exists (usually it will not), so this run starts from an empty one: the session id is shared by every /fix-bug run in the session, so an earlier run abandoned before Step 9 would otherwise leak its notes into this one. Never delete it again afterwards, including when Step 3 sends you back to Step 1 or Step 2; those loops are part of the same run and their notes must survive.

While working through Steps 1-8, whenever one of the following occurs, immediately append a line to that file — do not wait until the end to reconstruct these from memory:

  • The confirmed Condition / Expected / Actual differs from what the user first reported, or the documentation conflicted with the report and you resolved which is correct → Bug report clarifications
  • You established — or later revised — which line(s) or logic are responsible and why they misbehave, including when the fix actually applied differs from the one formulated in Step 5 → Root cause
  • You investigated a suspected cause, code path, or reproduction approach and eliminated it → Ruled out
  • You considered alternatives and chose one, and why → Tradeoffs
  • You modified or deleted test code that was already committed, and why → Test changes

Read the full file on GitHub · 177 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 · 177 lines · 86 tokens per session scan A 613d4f527918

Subscribe to this mod's changes

fix-bug is a skill published in the GitHub repository nowsprinting/unity-coding-skills (19 stars, last pushed 2d ago), licensed Unlicense. It adds 86 tokens to every session and 2,309 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 2026-08-30.

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