systematic-debugging

A step-by-step debugging method that investigates and analyzes a failure before changing code. Debugging means finding and fixing the cause of software that behaves incorrectly.

In plain words
What is it for?
Use it for failing tests, unexpected behavior, error messages, regressions, or any situation where you are tempted to try fixes without understanding the problem.
Why use it?
It reduces random fix attempts and the new problems they can create by first reproducing the issue and tracing its 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/jpm1118/threadwork/systematic-debugging
Any agent
npx skills add JPM1118/Threadwork --skill systematic-debugging
Clone the repo
git clone --depth 1 https://github.com/JPM1118/Threadwork

Made for: Claude Code, Codex.

Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,945 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 $0.00000 $0.01945
Opus 5 $0.00000 $0.00972
Sonnet 5 $0.00000 $0.00389
Haiku 4.5 $0.00000 $0.00194

Measured yesterday against content hash 87816f0f5522, 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/systematic-debugging/SKILL.md · 315 lines

How it starts

The opening of the file, as written. The whole thing — 315 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Systematic Debugging Skill

Resolve issues through root cause discovery rather than random fix attempts. This skill prevents thrashing and achieves 95%+ first-time fix rates.

Core Principle

UNDERSTAND BEFORE YOU FIX

Random fix attempts waste time and often introduce new bugs. Systematic investigation finds the real problem.

When to Use This Skill

Use this skill when:

  • Tests are failing
  • A feature isn't working as expected
  • You encounter an error message
  • Something that worked before is now broken
  • You're tempted to "just try something"

The Four-Phase Framework

┌─────────────────────────────────────────────────────────────┐
│                 Systematic Debugging Flow                    │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│  Phase 1: INVESTIGATE                                       │
│     ↓     Read errors, reproduce, examine changes           │
│                                                             │
│  Phase 2: ANALYZE                                           │
│     ↓     Find working examples, compare patterns           │
│                                                             │
│  Phase 3: HYPOTHESIZE                                       │
│     ↓     Form theories, test with minimal changes          │
│                                                             │
│  Phase 4: IMPLEMENT                                         │
│           Create failing test, implement fix, verify        │
│                                                             │
└─────────────────────────────────────────────────────────────┘

Phase 1: Root Cause Investigation

Step 1.1: Read the Error Carefully

Don't skim. Read the ENTIRE error message:

  • Error type/name
  • Error message
  • Stack trace (every line)
  • File paths and line numbers
  • Any additional context
# Run the failing test/command
npm test -- --grep "failing test name"

# Read ALL output, not just the failure summary

Read the full file on GitHub · 315 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 · 315 lines · 0 tokens per session scan A 87816f0f5522

Subscribe to this mod's changes

systematic-debugging is a skill published in the GitHub repository JPM1118/Threadwork (5 stars, last pushed 8mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 1,945 tokens. 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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