diagnosing-bugs

diagnosing-bugs is a skill for Claude Code, Codex from gongyijie85/mattpocock-skills-dsh. It costs 40 tokens per session (2,003 once invoked), scanned A, a copy of diagnosing-bugs, MIT.

A structured method for investigating difficult software bugs and performance slowdowns. It builds a reliable way to reproduce the problem, then tests possible causes.

In plain words
What is it for?
Use it to debug failures, investigate slow code, create focused tests, inspect relevant project decisions, and document evidence for the diagnosis.
Why use it?
It prevents guesswork when a bug is intermittent, complex, or hard to measure, and keeps diagnostic evidence clear while protecting secrets.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it to debug failures, investigate slow code, create focused tests, inspect relevant project decisions, and document evidence for the diagnosis.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/gongyijie85/mattpocock-skills-dsh/diagnosing-bugs
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.

Any agent
npx skills add gongyijie85/mattpocock-skills-dsh --skill diagnosing-bugs
Clone the repo
git clone --depth 1 https://github.com/gongyijie85/mattpocock-skills-dsh

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/gongyijie85/mattpocock-skills-dsh/diagnosing-bugs/github.svg)](https://agentmods.dev/skills/gongyijie85/mattpocock-skills-dsh/diagnosing-bugs)
Your own site
<a href="https://agentmods.dev/skills/gongyijie85/mattpocock-skills-dsh/diagnosing-bugs"><img src="https://agentmods.dev/badge/skills/gongyijie85/mattpocock-skills-dsh/diagnosing-bugs/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for diagnosing-bugs

Your own site · 80×15
<a href="https://agentmods.dev/skills/gongyijie85/mattpocock-skills-dsh/diagnosing-bugs"><img src="https://agentmods.dev/badge/skills/gongyijie85/mattpocock-skills-dsh/diagnosing-bugs.svg" alt="Reviewed on agentmods" width="80" 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 2,003 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe.
Origin 100% 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 5.1 $0.00040 $0.02003
Opus 5 $0.00020 $0.01001
Sonnet 5 $0.00008 $0.00401
Haiku 4.5 $0.00004 $0.00200

Measured 12d ago against content hash 77f3cf31bc99, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, 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 12d 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** (show the invocation and its output, red
Origin

This is a copy

100% identical to diagnosing-bugs — 0 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.

skills/diagnosing-bugs/SKILL.md · 139 lines

How it starts

The opening of the file, as written. The whole thing — 139 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.

Redact

This skill has you show commands, outputs and captured artifacts. Redact every secret first: write <REDACTED> in its place. Build loops against env vars, so the credential stays in the environment rather than in what you show. Captured artifacts carry auth headers: quote only the lines that carry the signal.

If the redacted output is not enough to diagnose the bug, say so and ask the user.

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, 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) that drives the UI and 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.

Read the full file on GitHub · 139 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. 12d ago First seen · 139 lines · 40 tokens per session scan A 77f3cf31bc99

Subscribe to this mod's changes

diagnosing-bugs is a skill published in the GitHub repository gongyijie85/mattpocock-skills-dsh (13 stars, last pushed yesterday), licensed MIT. It adds 40 tokens to every session and 2,003 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 100% identical to diagnosing-bugs, differing in 0 lines, and is treated as a copy.

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