systematic-debugging

A step-by-step method for finding the real cause of bugs, failed tests, and unexpected behavior.

In plain words
What is it for?
Use it to reproduce an issue, trace it to its cause, test focused explanations, apply a fix, and check that the full test suite still passes.
Why use it?
It prevents guesswork and changes that hide the original problem or introduce new ones.

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/yimwoo/hotl-plugin/systematic-debugging
Any agent
npx skills add yimwoo/hotl-plugin --skill systematic-debugging
Clone the repo
git clone --depth 1 https://github.com/yimwoo/hotl-plugin

Made for: Claude Code, Codex.

Per session 22 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 230 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 $0.00022 $0.00230
Opus 5 $0.00011 $0.00115
Sonnet 5 $0.00004 $0.00046
Haiku 4.5 $0.00002 $0.00023

Measured 2d ago against content hash cb5421eab794, 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 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/systematic-debugging/SKILL.md · 35 lines

What it actually says

Systematic Debugging

Four Phases

Phase 1: Reproduce

  • Get a minimal, reliable reproduction
  • Never fix what you can't reproduce

Phase 2: Understand

  • Read the error message fully — the answer is often there
  • Trace the call path from symptom to root cause
  • Check: recent changes, environment differences, assumptions about inputs

Phase 3: Hypothesize

  • Form 1-3 specific hypotheses about root cause
  • Test each hypothesis with the smallest possible change
  • Never change multiple things at once

Phase 4: Fix and Verify

  • Fix the root cause, not the symptom
  • Run the reproduction case — confirm fixed
  • Run full test suite — confirm no regressions
  • Invoke hotl:verification-before-completion

Red Flags

  • "Let me try X and see what happens" without a hypothesis
  • Changing multiple things before verifying
  • Marking done without running full tests
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 · 35 lines · 22 tokens per session scan A cb5421eab794

Subscribe to this mod's changes

systematic-debugging is a skill published in the GitHub repository yimwoo/hotl-plugin (26 stars, last pushed 1mo ago), licensed MIT. It adds 22 tokens to every session and 230 once invoked, about $0.0001 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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