systematic-debugging

A step-by-step method for diagnosing broken software when the cause is unclear.

In plain words
What is it for?
Use it for failing tests, crashes, stack traces, error logs, or incorrect behavior. It guides you to make a small fix and add a test that prevents the problem from returning.
Why use it?
It requires reproducing the problem and proving a specific cause before changing code, which reduces guesswork and symptom-only fixes.

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

Made for: Claude Code, Codex.

Per session 74 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 456 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 $0.00074 $0.00456
Opus 5 $0.00037 $0.00228
Sonnet 5 $0.00015 $0.00091
Haiku 4.5 $0.00007 $0.00046

Measured yesterday against content hash 06acaa565b01, 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 yesterday.

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.

claude/skills/systematic-debugging/SKILL.md · 37 lines

What it actually says

Systematic debugging

Fix the cause, not the symptom — and prove the cause before you touch code.

The method

  1. Reproduce — get a reliable, minimal repro (a failing test is ideal). No repro → no fix.
  2. Hypothesize — one specific, falsifiable guess about the cause ("X is null because Y").
  3. Prove it — instrument/log/inspect to confirm the hypothesis before editing. If the evidence contradicts it, form a new hypothesis. Don't guess-and-change.
  4. Minimal fix — change the smallest thing that addresses the proven root cause.
  5. Verify — re-run the repro; it passes. Run the surrounding tests; nothing regressed. (See verification-before-completion.)
  6. Guard — add/extend a test that would have caught it, so it can't silently return.

For a nasty one, delegate to the debugger subagent (or the triage command) — it forms a hypothesis, proves it, and proposes the minimal fix.

Red flags — you're not debugging, you're flailing

  • Changing code before reproducing the problem.
  • Fixing the symptom (swallow the error, bump the timeout) instead of the cause.
  • Several changes at once — you won't know which one mattered.
  • "It went away" with no explanation of why — it'll come back.
  • Re-running hoping for a different result without changing your hypothesis.

Done means

Root cause proven (not assumed) · minimal fix · repro now green · a regression test added · no new failures. Anything less is UNVERIFIED.

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. yesterday First seen · 37 lines · 74 tokens per session scan A 06acaa565b01

Subscribe to this mod's changes

systematic-debugging is a skill published in the GitHub repository dshakes/compass (19 stars, last pushed 7d ago), licensed MIT. It adds 74 tokens to every session and 456 once invoked, about $0.0004 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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