systematic-debugging

systematic-debugging is a skill for Claude Code, Codex from HezaoHezao/poirot. It costs 16 tokens per session (2,592 once invoked), scanned A, original, MIT.

A four-phase method for debugging software by finding the underlying cause before changing code.

In plain words
What is it for?
It helps investigate failing tests, bugs, unexpected behavior, slow programs, build failures, and integration problems.
Why use it?
It replaces guesswork and quick patches with a small, repeatable test or command that reproduces the exact 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/hezaohezao/poirot/systematic-debugging
Any agent
npx skills add HezaoHezao/poirot --skill systematic-debugging
Clone the repo
git clone --depth 1 https://github.com/HezaoHezao/poirot

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 systematic-debugging

README.md
[![agentmods](https://agentmods.dev/badge/skills/hezaohezao/poirot/systematic-debugging.svg)](https://agentmods.dev/skills/hezaohezao/poirot/systematic-debugging)
Your own site
<a href="https://agentmods.dev/skills/hezaohezao/poirot/systematic-debugging"><img src="https://agentmods.dev/badge/skills/hezaohezao/poirot/systematic-debugging.svg" alt="Measured on agentmods" height="20"></a>
Per session 16 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,592 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. 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 $0.00016 $0.02592
Opus 5 $0.00008 $0.01296
Sonnet 5 $0.00003 $0.00518
Haiku 4.5 $0.00002 $0.00259

Measured 5d ago against content hash 386ba0fe023e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

systematic-debugging 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 5d 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.

Makes network callslowCapability

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

2. **HTTP script / curl** against a running dev server.
poirot/backend/agents/skill/builtin_skills/core/systematic-debugging/SKILL.md · 347 lines

How it starts

The opening of the file, as written. The whole thing — 347 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Systematic Debugging

Overview

Random fixes waste time and create new bugs. Quick patches mask underlying issues.

Core principle: ALWAYS find root cause before attempting fixes. Symptom fixes are failure.

The Iron Law

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

If you haven't completed Phase 1, you cannot propose fixes.

The Feedback Loop Rule

The feedback loop is the debugging work. Before reading code to build a theory, create or identify a tight command that can go red on the user's exact symptom and green when the bug is fixed. A tight loop is fast, deterministic, agent-runnable, and specific enough to catch this bug — not merely "doesn't crash".

When a clean repro is hard, spend disproportionate effort building the loop.

When to Use

Use for ANY technical issue: test failures, bugs in production, unexpected behavior, performance problems, build failures, integration issues.

Use ESPECIALLY when:

  • Under time pressure (emergencies make guessing tempting)
  • "Just one quick fix" seems obvious
  • You've already tried multiple fixes
  • Previous fix didn't work
  • You don't fully understand the issue

The Four Phases

You MUST complete each phase before proceeding to the next.


Phase 1: Root Cause Investigation

BEFORE attempting ANY fix:

1. Read Error Messages Carefully

  • Don't skip past errors or warnings
  • They often contain the exact solution
  • Read stack traces completely
  • Note line numbers, file paths, error codes

Action: Use read_file on the relevant source files. Use bash with grep to find the error string in the codebase.

2. Build a Tight Feedback Loop

  • Can you trigger the user's exact symptom with one command?
  • Does the command fail for this bug and only pass once the bug is fixed?
  • Is it fast enough to run repeatedly?
  • Is it deterministic?
  • If not reproducible → gather more data, don't guess.

Ways to construct a loop — try in roughly this order:

  1. Failing test at the seam that reaches the bug: unit, integration, or e2e.
  2. HTTP script / curl against a running dev server.
  3. CLI invocation with fixture input, diffing stdout/stderr against expected.
  4. Headless browser script (Playwright/Puppeteer) asserting on DOM/console/network.
  5. Replay a captured trace: HAR, request payload, event log, webhook body.
  6. Throwaway harness that boots the smallest useful slice of the system.
  7. Property / fuzz loop when the bug is intermittent wrong output.
  8. Bisection harness suitable for git bisect run.
  9. Differential loop comparing old vs new version, two configs, or two datasets.

Read the full file on GitHub · 347 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. 5d ago First seen · 347 lines · 16 tokens per session scan A 386ba0fe023e

Subscribe to this mod's changes

systematic-debugging is a skill published in the GitHub repository HezaoHezao/poirot (215 stars, last pushed 1mo ago), licensed MIT. It adds 16 tokens to every session and 2,592 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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