debug

A systematic debugging process for investigating bugs, failed tests, broken builds, performance problems, and other unexpected behavior.

In plain words
What is it for?
Use it when diagnosing a reproducible or intermittent software problem, following its investigation, reproduction, data-gathering, and analysis phases.
Why use it?
It requires finding and confirming the root cause before proposing a fix, reducing guesswork and repeated patches.

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/guild-agents/guild/debug
Any agent
npx skills add Guild-Agents/guild --skill debug
Clone the repo
git clone --depth 1 https://github.com/Guild-Agents/guild

Made for: Claude Code, Codex.

Per session 33 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,215 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 $0.00033 $0.01215
Opus 5 $0.00016 $0.00607
Sonnet 5 $0.00007 $0.00243
Haiku 4.5 $0.00003 $0.00121

Measured yesterday against content hash b8e44fcf2a6f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

debug 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.

.claude/skills/debug/SKILL.md · 146 lines

How it starts

The opening of the file, as written. The whole thing — 146 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Systematic Debugging

Random fixes waste time and create new bugs. Quick patches mask underlying issues.

Core principle: ALWAYS find root cause before attempting fixes.

Usage

/debug

Invoke this skill when encountering any bug, test failure, or unexpected behavior. Follow the four phases in order.

When to use

  • Test failures
  • Bugs in production
  • Unexpected behavior
  • Performance problems
  • Build failures
  • Integration issues

Use this ESPECIALLY when:

  • Under time pressure (emergencies make guessing tempting)
  • "Just one quick fix" seems obvious
  • You've already tried multiple fixes
  • Previous fix didn't work

The Iron Law

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

If you haven't completed Phase 1, you cannot propose fixes.

The Four Phases

Complete each phase before proceeding to the next.

Phase 1: Root Cause Investigation

BEFORE attempting ANY fix:

  1. Read Error Messages Carefully

    • Don't skip past errors or warnings
    • Read stack traces completely
    • Note line numbers, file paths, error codes
  2. Reproduce Consistently

    • Can you trigger it reliably?
    • What are the exact steps?
    • If not reproducible, gather more data — don't guess
  3. Check Recent Changes

    • What changed that could cause this?
    • Git diff, recent commits
    • New dependencies, config changes
  4. Gather Evidence in Multi-Component Systems

    • Log what data enters each component boundary
    • Log what data exits each component boundary
    • Verify environment/config propagation
    • Run once to gather evidence showing WHERE it breaks
    • THEN investigate that specific component
  5. Trace Data Flow

    • Where does the bad value originate?
    • What called this with the bad value?
    • Keep tracing up until you find the source
    • Fix at source, not at symptom

Phase 2: Pattern Analysis

  1. Find Working Examples — locate similar working code in the same codebase
  2. Compare Against References — read reference implementations COMPLETELY, don't skim
  3. Identify Differences — list every difference between working and broken, however small
  4. Understand Dependencies — what components, settings, environment does it need?

Read the full file on GitHub · 146 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 · 146 lines · 33 tokens per session scan A b8e44fcf2a6f

Subscribe to this mod's changes

debug is a skill published in the GitHub repository Guild-Agents/guild (4 stars, last pushed 1mo ago), licensed MIT. It adds 33 tokens to every session and 1,215 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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