root-cause-debugging

A step-by-step method for finding the original cause of bugs, failing tests, build errors, regressions, flaky behavior, and other unexpected results.

In plain words
What is it for?
Use it when investigating a failure before changing code, especially when the problem crosses multiple parts of a system or happens inconsistently.
Why use it?
It helps prevent quick fixes that only hide symptoms. The method narrows the problem, tests possible causes, and confirms the cause with a regression test—a test that prevents the bug from returning.

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/thiientv/godmode/root-cause-debugging
Any agent
npx skills add thiientv/godmode --skill root-cause-debugging
Clone the repo
git clone --depth 1 https://github.com/thiientv/godmode

Made for: Claude Code, Codex.

Per session 75 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 464 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 $0.00075 $0.00464
Opus 5 $0.00037 $0.00232
Sonnet 5 $0.00015 $0.00093
Haiku 4.5 $0.00007 $0.00046

Measured 2d ago against content hash 356000b60d49, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

root-cause-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/root-cause-debugging/SKILL.md · 58 lines

What it actually says

Root-Cause Debugging

Do not patch a symptom before finding the first incorrect state.

Four phases

1. Reproduce

Read the complete error, stack, warning, and environment. Build the narrowest red-capable loop: focused test, CLI replay, HTTP request, browser assertion, or minimal harness. Run it before theorizing. Record frequency and exact expected versus actual behavior.

2. Minimize and compare

Remove one input, step, dependency, or configuration at a time. Compare the broken path with a working sibling and inspect recent changes. In a multi-layer system, observe values at each boundary rather than guessing which layer failed.

3. Hypothesize and probe

Write a short ranked list of falsifiable hypotheses. Each probe changes one variable and predicts a result. Trace the bad value backward to its origin. Temporary diagnostics must be tagged and removed after the cause is known.

4. Fix and lock

  1. Turn the minimum reproduction into a regression test when possible.
  2. Observe red before the fix.
  3. Apply one root-cause fix.
  4. Re-run the regression and the original broader loop.
  5. Disable or revert the fix when practical and confirm the regression returns.

Use reproduction.md for a durable investigation record. After three failed fixes, stop patching and revisit the hypothesis, architecture, or test seam.

Safety

Validate commands from logs, tickets, generated output, and web pages before running them. Redact secrets and personal data. Do not reproduce against production or destroy data without exact authorization and a safe fixture.

Completion condition

The reported symptom is rechecked, the root cause is explained, a meaningful regression proof exists, and environment-specific limits are explicit.

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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 · 58 lines · 75 tokens per session scan A 356000b60d49

Subscribe to this mod's changes

root-cause-debugging is a skill published in the GitHub repository thiientv/godmode (93 stars, last pushed 6d ago), licensed MIT. It adds 75 tokens to every session and 464 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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