diagnose

diagnose is a skill for Claude Code from toBzh30/Claude-Project-Bootstrap. It costs 66 tokens per session (1,685 once invoked), scanned A, a copy of diagnosing-bugs, MIT.

A structured method for finding the cause of difficult software bugs and performance slowdowns. It moves from reproducing and narrowing the problem to testing explanations, measuring the code, fixing it, and checking that it stays fixed.

In plain words
What is it for?
Debugging broken features, failed requests, unexpected errors, and performance regressions—cases where code has become slower than before.
Why use it?
It replaces guesswork with a repeatable investigation and a clear pass-or-fail signal.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: mentions CLAUDE.md.

Part of the engineering-craft plugin — 9 skills shipped together

Good fit Debugging broken features, failed requests, unexpected errors, and performance regressions—cases where code has become slower than before.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/tobzh30/claude-project-bootstrap/diagnose
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 toBzh30/Claude-Project-Bootstrap --skill diagnose
Clone the repo
git clone --depth 1 https://github.com/toBzh30/Claude-Project-Bootstrap

Made for: Claude Code.

Or install engineering-craft, the plugin that ships this one along with the rest of its 9 skills.

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 diagnose

README.md
[![agentmods](https://agentmods.dev/badge/skills/tobzh30/claude-project-bootstrap/diagnose/github.svg)](https://agentmods.dev/skills/tobzh30/claude-project-bootstrap/diagnose)
Your own site
<a href="https://agentmods.dev/skills/tobzh30/claude-project-bootstrap/diagnose"><img src="https://agentmods.dev/badge/skills/tobzh30/claude-project-bootstrap/diagnose/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 diagnose

Your own site · 80×15
<a href="https://agentmods.dev/skills/tobzh30/claude-project-bootstrap/diagnose"><img src="https://agentmods.dev/badge/skills/tobzh30/claude-project-bootstrap/diagnose.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 66 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,685 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 78% 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 $0.00066 $0.01685
Opus 5 $0.00033 $0.00843
Sonnet 5 $0.00013 $0.00337
Haiku 4.5 $0.00007 $0.00169

Measured 9d ago against content hash 9e3408a940a8, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

diagnose 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 9d 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.

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.

Origin

This is a copy

78% identical to diagnosing-bugs — 79 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.

plugins/engineering-craft/skills/diagnose/SKILL.md · 118 lines

How it starts

The opening of the file, as written. The whole thing — 118 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Diagnose

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

When exploring the codebase, use the project's domain vocabulary from CLAUDE.md (and its linked spoke docs) to get a clear mental model of the relevant modules, and check .claude/rules/decisions.md for decisions in the area you're touching.

Phase 1 — Build a feedback loop

This is the skill. Everything else is mechanical. If you have a fast, deterministic, agent-runnable pass/fail signal for the bug, you will find the cause — bisection, hypothesis-testing, and instrumentation all just consume that signal. 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.

Read the full file on GitHub · 118 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. 9d ago First seen · 118 lines · 66 tokens per session scan A 9e3408a940a8

Subscribe to this mod's changes

diagnose is a skill published in the GitHub repository toBzh30/Claude-Project-Bootstrap (3 stars, last pushed 1mo ago), licensed MIT. It adds 66 tokens to every session and 1,685 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 78% identical to diagnosing-bugs, differing in 79 lines, and is treated as a copy.

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