diagnosing-bugs

diagnosing-bugs is a skill for Claude Code, Codex from chinkan/RustFox. It costs 40 tokens per session (1,985 once invoked), scanned A, a copy of diagnosing-bugs, MIT.

A structured process for finding the cause of difficult bugs and performance slowdowns by first creating a reliable pass-or-fail test, then testing possible explanations.

In plain words
What is it for?
Use it to debug failing, broken, or slow behavior with tests, command-line checks, HTTP requests, browser automation, captured traces, or instrumentation.
Why use it?
It replaces guesswork with feedback that shows whether an attempted fix addresses the reported problem.

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/chinkan/rustfox/diagnosing-bugs
Any agent
npx skills add chinkan/RustFox --skill diagnosing-bugs
Clone the repo
git clone --depth 1 https://github.com/chinkan/RustFox

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for diagnosing-bugs

README.md
[![agentmods](https://agentmods.dev/badge/skills/chinkan/rustfox/diagnosing-bugs.svg)](https://agentmods.dev/skills/chinkan/rustfox/diagnosing-bugs)
Your own site
<a href="https://agentmods.dev/skills/chinkan/rustfox/diagnosing-bugs"><img src="https://agentmods.dev/badge/skills/chinkan/rustfox/diagnosing-bugs.svg" alt="Measured on agentmods" height="20"></a>
Per session 40 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,985 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. Scan, not verified.
Origin 95% copy Near-identical to another mod 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 $0.00040 $0.01985
Opus 5 $0.00020 $0.00992
Sonnet 5 $0.00008 $0.00397
Haiku 4.5 $0.00004 $0.00198

Measured 4d ago against content hash 7a0779480f32, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

diagnosing-bugs scanned grade A with 1 finding 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 4d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/hitl-loop.template.sh), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

Phase 1 is done when the loop is **tight** and **red-capable**: you can name **one command** — a script path, a test invocation, a curl — that you have **already run at least once** (paste the invocation and its output),
Origin

This is a copy

95% identical to diagnosing-bugs — 64 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.agents/skills/diagnosing-bugs/SKILL.md · 135 lines

How it starts

The opening of the file, as written. The whole thing — 135 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Diagnosing Bugs

A discipline for hard bugs. Skip phases only when explicitly justified.

When exploring the codebase, read CONTEXT.md (if it exists) to get a clear mental model of the relevant modules, and check ADRs in the area you're touching.

Phase 1 — Build a feedback loop

This is the skill. Everything else is mechanical. If you have a tight pass/fail signal for the bug — one that goes red on this bug — you will find the cause; bisection, hypothesis-testing, and instrumentation all just consume it. If you don't have one, no amount of staring at code will save you.

Spend disproportionate effort here. Be aggressive. Be creative. Refuse to give up.

Ways to construct one — try them in roughly this order

  1. Failing test at whatever seam reaches the bug — unit, integration, e2e.
  2. Curl / HTTP script against a running dev server.
  3. CLI invocation with a fixture input, diffing stdout against a known-good snapshot.
  4. Headless browser script (Playwright / Puppeteer) — drives the UI, asserts on DOM/console/network.
  5. Replay a captured trace. Save a real network request / payload / event log to disk; replay it through the code path in isolation.
  6. Throwaway harness. Spin up a minimal subset of the system (one service, mocked deps) that exercises the bug code path with a single function call.
  7. Property / fuzz loop. If the bug is "sometimes wrong output", run 1000 random inputs and look for the failure mode.
  8. Bisection harness. If the bug appeared between two known states (commit, dataset, version), automate "boot at state X, check, repeat" so you can git bisect run it.
  9. Differential loop. Run the same input through old-version vs new-version (or two configs) and diff outputs.
  10. HITL bash script. Last resort. If a human must click, drive them with scripts/hitl-loop.template.sh so the loop is still structured. Captured output feeds back to you.

Build the right feedback loop, and the bug is 90% fixed.

Read the full file on GitHub · 135 lines

Files

What ships with it

2 files 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. 4d ago First seen · 135 lines · 40 tokens per session scan A 7a0779480f32

Subscribe to this mod's changes

diagnosing-bugs is a skill published in the GitHub repository chinkan/RustFox (7 stars, last pushed 27d ago), licensed MIT. It adds 40 tokens to every session and 1,985 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). It is 95% identical to diagnosing-bugs, differing in 64 lines, and is treated as a copy.

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