systematic-debugging

systematic-debugging is a skill for Claude Code, Codex from drvoss/everything-copilot-cli. It costs 39 tokens per session (2,272 once invoked), scanned A, original, MIT.

A four-phase method for investigating bugs whose causes are unclear or that keep returning after a quick fix.

In plain words
What is it for?
It helps reproduce intermittent bugs, narrow down triggering inputs, write a failing test, and verify a lasting fix.
Why use it?
It replaces random trial-and-error changes with a reproducible investigation that targets the underlying cause.

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/drvoss/everything-copilot-cli/systematic-debugging
Any agent
npx skills add drvoss/everything-copilot-cli --skill systematic-debugging
Clone the repo
git clone --depth 1 https://github.com/drvoss/everything-copilot-cli

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/drvoss/everything-copilot-cli/systematic-debugging.svg)](https://agentmods.dev/skills/drvoss/everything-copilot-cli/systematic-debugging)
Your own site
<a href="https://agentmods.dev/skills/drvoss/everything-copilot-cli/systematic-debugging"><img src="https://agentmods.dev/badge/skills/drvoss/everything-copilot-cli/systematic-debugging.svg" alt="Measured on agentmods" height="20"></a>
Per session 39 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,272 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 $0.02272
Opus 5 $0.00019 $0.01136
Sonnet 5 $0.00008 $0.00454
Haiku 4.5 $0.00004 $0.00227

Measured yesterday against content hash 52bc80f6e6ec, 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.

skills/development/systematic-debugging/SKILL.md · 249 lines

How it starts

The opening of the file, as written. The whole thing — 249 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Systematic Debugging

A structured 4-phase methodology for diagnosing and fixing non-obvious bugs. Prevents the common failure modes of "shotgun debugging" (random changes hoping something sticks) and "symptom patching" (fixing the visible error without understanding the cause).

When to Use

  • A bug has resisted one or more quick-fix attempts
  • The bug only appears in certain environments (prod but not dev, intermittent)
  • The cause is unclear after an initial look
  • A "fixed" bug keeps coming back
  • Multiple engineers have looked at it without resolution

When NOT to Use

Instead of systematic-debugging Use
Obvious typo or off-by-one Fix directly
Build/compilation failure fix-build-errors skill
Performance problem (not a bug) profiling tools
Security vulnerability security-scan skill

The 4-Phase Process

Phase 1 — Reproduce

A bug you cannot reproduce reliably cannot be debugged reliably.

Goal: Get a 100% reproducible test case that triggers the bug on demand.

# 1. Note the exact symptoms: error message, stack trace, request/response
# 2. Identify the minimum inputs that trigger it
# 3. Write a failing test that captures the reproduction

# Find the code path involved
Select-String -Path "src\\**\\*.ts" -Pattern "<error keyword>"

# Check recent changes
git --no-pager log --oneline -20
git --no-pager diff HEAD~5 -- <suspect file>

Reproduction criteria:

  • Bug triggers on demand with a specific input or sequence
  • Bug does NOT trigger with a slightly different (correct) input
  • Reproduction is encoded as a failing test

When it is safe, run the minimal reproduction at least twice and record both commands and outputs; one observation is not proof of reproducibility. If outcomes vary, label the reproduction status intermittent rather than hiding the variation.

Before handing the issue to diagnosis or another session, produce a reproduction brief with:

Read the full file on GitHub · 249 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. yesterday First seen · 249 lines · 39 tokens per session scan A 52bc80f6e6ec

Subscribe to this mod's changes

systematic-debugging is a skill published in the GitHub repository drvoss/everything-copilot-cli (45 stars, last pushed 8d ago), licensed MIT. It adds 39 tokens to every session and 2,272 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 2026-09-03.

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