systematic-debugging

A four-phase method for finding the root cause of software bugs: observe the evidence, form hypotheses, test them, and implement the confirmed fix.

In plain words
What is it for?
Investigating errors, crashes, incorrect output, and regressions by reproducing the problem, ranking possible causes, testing them, and applying the verified solution.
Why use it?
It reduces trial-and-error changes and encourages decisions based on reproducible symptoms and test results.

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/vimalk0703/shipworthy/systematic-debugging
Any agent
npx skills add Vimalk0703/shipworthy --skill systematic-debugging
Clone the repo
git clone --depth 1 https://github.com/Vimalk0703/shipworthy

Made for: Claude Code, Codex.

Per session 39 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 673 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 $0.00039 $0.00673
Opus 5 $0.00019 $0.00336
Sonnet 5 $0.00008 $0.00135
Haiku 4.5 $0.00004 $0.00067

Measured 2d ago against content hash ce0c7ca32fcf, 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/debugging/systematic-debugging/SKILL.md · 68 lines

How it starts

The opening of the file, as written. The whole thing — 68 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Systematic Debugging

The Anti-Pattern This Prevents

Trial-and-error debugging: change something, see if it works, repeat. This approach takes 2-3 hours and has a 50% first-time fix rate. Systematic debugging takes 15-30 minutes with a 95% first-time fix rate.

The 4 Phases

Phase 1: Observe

Gather evidence before forming theories.

  • What exactly is the symptom? (error message, wrong output, crash)
  • When does it happen? (always, sometimes, only in production)
  • What changed recently? (git log, recent deploys, config changes)
  • Can you reproduce it reliably?
  • Read the FULL error message and stack trace

Phase 2: Hypothesize

Form testable theories based on evidence.

  • What could cause this symptom?
  • List 2-3 hypotheses, ranked by likelihood
  • Each hypothesis must be testable — "something is wrong" is not a hypothesis
  • Consider: is this a code bug, a data bug, a config bug, or an environment bug?

Phase 3: Test

Test each hypothesis methodically.

  • Start with the most likely hypothesis
  • Design a test that would CONFIRM or ELIMINATE the hypothesis
  • Run the test. Read the results carefully.
  • If confirmed: proceed to Phase 4
  • If eliminated: move to the next hypothesis

Phase 4: Implement

Fix the root cause, not the symptom.

  • Write a test that reproduces the bug FIRST (TDD applies to bugs too)
  • Implement the fix
  • Run the reproducing test — it should pass now
  • Run the full test suite — nothing else should break
  • Verify the fix in the original context where the bug was observed

The 3-Fix Rule

If 3 attempted fixes don't resolve the issue, STOP.

You're likely:

  • Fixing a symptom, not the root cause
  • Working with wrong assumptions
  • Dealing with an architectural issue that requires a different approach

When you hit the 3-fix limit:

  1. Step back and re-examine your assumptions
  2. Re-read the error messages and logs from scratch
  3. Consider whether the bug is in a different layer than you're looking at
  4. Discuss with the user before proceeding

Read the full file on GitHub · 68 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. 2d ago First seen · 68 lines · 39 tokens per session scan A ce0c7ca32fcf

Subscribe to this mod's changes

systematic-debugging is a skill published in the GitHub repository Vimalk0703/shipworthy (7 stars, last pushed 4mo ago), licensed MIT. It adds 39 tokens to every session and 673 once invoked, about $0.0002 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 2026-08-31.

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