systematic-debugging

A debugging method that investigates the underlying cause of a bug, failed test, crash, or unexpected behaviour before changing code.

In plain words
What is it for?
It is for reproducing failures, reading errors and stack traces, isolating causes, and then choosing a fix based on evidence.
Why use it?
It reduces guess-and-check fixes that address symptoms, fail to solve the issue, or create new problems.

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/khaledsaeed18/dotclaude/systematic-debugging
Any agent
npx skills add KhaledSaeed18/dotclaude --skill systematic-debugging
Clone the repo
git clone --depth 1 https://github.com/KhaledSaeed18/dotclaude

Made for: Claude Code, Codex.

Per session 61 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,115 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 $0.00061 $0.01115
Opus 5 $0.00030 $0.00558
Sonnet 5 $0.00012 $0.00223
Haiku 4.5 $0.00006 $0.00112

Measured 2d ago against content hash 019453806e3d, 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.

.claude-plugin/plugins/engineering/skills/systematic-debugging/SKILL.md · 61 lines

How it starts

The opening of the file, as written. The whole thing — 61 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Find the root cause before you touch a line of code. A fix that targets a symptom you don't understand either fails or moves the bug somewhere else, and each blind attempt makes the next one harder to reason about. Investigation first is not the slow path — it is the fast one.

The one rule

No fix before you can name the root cause. If you can't say "the bug happens because X", you are still investigating, not fixing. The moment you feel "let me just try changing this and see" — stop. That instinct is the thing this skill exists to interrupt.

This holds hardest exactly when it feels most skippable: under time pressure, when the bug "looks simple", when you've already tried two things. Simple bugs have root causes too, and guess-and-check is slower than it feels because every wrong attempt has to be unwound.

Step 1: Investigate the root cause

Do all of this before forming any fix.

  • Read the actual error. The full message, the full stack trace, line numbers, error codes. The answer is often already written there. Don't skim past it to the part you assume is the problem.
  • Reproduce it reliably. What exact steps trigger it? Every time, or intermittently? If you can't reproduce it, you can't confirm a fix — gather more data rather than guessing.
  • Check what changed. git diff, recent commits, new dependencies, config or environment differences. A bug that just appeared usually has a recent cause.
  • Instrument the boundaries when the system has multiple layers (request → service → database, CI → build → sign). Log what enters and what leaves each boundary, run once, and read where the data first goes wrong. Find the failing layer with evidence before you reason about why that layer fails.
  • Trace the bad value to its origin. When the error surfaces deep in a call stack, work backward: where did this value come from, what passed it in, and up the chain until you reach the true source. Fix it there, not where it happened to blow up.

Read the full file on GitHub · 61 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 · 61 lines · 61 tokens per session scan A 019453806e3d

Subscribe to this mod's changes

systematic-debugging is a skill published in the GitHub repository KhaledSaeed18/dotclaude (4 stars, last pushed 7d ago), licensed MIT. It adds 61 tokens to every session and 1,115 once invoked, about $0.0003 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.