debug

A step-by-step method for finding the underlying cause of test failures, runtime errors, or unexpected behavior. It starts by examining evidence, ranking possible causes, and narrowing the problem before changing code.

In plain words
What is it for?
Use it to investigate error messages and stack traces, reproduce failures with small inputs, test hypotheses, and apply verified fixes.
Why use it?
It helps avoid random fixes that only hide symptoms and may cause new failures elsewhere.

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/epicsagas/epic-harness/debug
Any agent
npx skills add epicsagas/epic-harness --skill debug
Clone the repo
git clone --depth 1 https://github.com/epicsagas/epic-harness

Made for: Claude Code, Codex.

Per session 26 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,045 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 $0.00026 $0.01045
Opus 5 $0.00013 $0.00522
Sonnet 5 $0.00005 $0.00209
Haiku 4.5 $0.00003 $0.00104

Measured 2d ago against content hash 6e3806ead344, 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 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/debug/SKILL.md · 96 lines

How it starts

The opening of the file, as written. The whole thing — 96 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Debug — Systematic Debugging

Iron Law

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST. Symptom fixes are whack-a-mole debugging.

Process

0. Recall

  • Query the knowledge graph: epic mem search "ERROR_MESSAGE_OR_FILE" for the error message or file name
  • Check if a resolution or pattern node exists for this error category
  • If a past resolution exists, apply it directly instead of re-debugging from scratch

Why: Past resolutions save 10-30 minutes of re-investigation. The knowledge graph exists so you don't repeat work.

1. Observe

  • Read the full error message and stack trace
  • Identify: What was expected? What actually happened?
  • Note the exact file, line, and function

Why: Precise observation prevents misdiagnosis. Most debug loops start from skimming the error instead of reading it fully.

2. Hypothesize

Form 2-3 possible causes. Rank by likelihood.

Why: Ranked hypotheses prevent random code changes. Even a wrong hypothesis narrows the search space.

3. Isolate

  • Narrow the scope: Binary search through recent changes
  • Reproduce minimally: Smallest input that triggers the error
  • Check assumptions: Print/log intermediate values
  • Bisect: git log --oneline -10 — when did it last work?

Why: Isolation proves the cause before you touch any code. Without it, you're guessing.

4. Fix

  • Fix the root cause, not the symptom
  • If the fix is a workaround, add a TODO with explanation

Why: Root cause fixes are permanent. Symptom patches rot and hide the real bug.

5. Verify

  • Run the failing test — must pass now
  • Run the full test suite — no regressions
  • If this was a bug, the regression test stays

Why: A passing fix without verification is wishful thinking. The full suite catches side effects.

6. Record

  • If the fix involved 3+ debug steps, record a resolution node via epic mem add --title "..." --type resolution --body "..."
  • Include: error category, root cause, solution approach
  • This enables future sessions to skip re-debugging the same class of issues

Read the full file on GitHub · 96 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 · 96 lines · 26 tokens per session scan A 6e3806ead344

Subscribe to this mod's changes

debug is a skill published in the GitHub repository epicsagas/epic-harness (17 stars, last pushed 2d ago), licensed Apache-2.0. It adds 26 tokens to every session and 1,045 once invoked, about $0.0001 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.

Related

Other skills, from other repositories

systematic-debugging

Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes.

obra/superpowers · 21 tokens

brainstorming

You MUST use this before any creative work - creating features, building components, adding functionality, or modifying behavior. Explores user intent, requirements and design before implementation.

obra/superpowers · 37 tokens

chat-pet-sprite-creation

Use when creating or changing VS Code chat pet sprite art, sprite sheets, state animations, eye treatments, Stable/Insiders variants, or pet transitions under src/vs/workbench/contrib/chat/browser/widget/media/chatPet.

microsoft/vscode · 53 tokens

cpu-profile-analysis

Analyze V8/Chrome CPU profiles (.cpuprofile) and DevTools trace files (Trace-.json). Use when: profiling performance, investigating slow functions, comparing code paths, finding bottlenecks, analyzing timeToRequest, understanding call trees from sampling profiler data, analyzing layout/paint/rendering, investigating…

microsoft/vscode · 71 tokens

agent-host-chat-contributions

Build and review cross-cutting agent-host chat behavior through lifecycle contributions. Use when adding turn lifecycle side effects, prompt or context injection, restored-history transformation, protocol-action observation, or when reviewing changes that add code to AgentSideEffects or AgentService.

microsoft/vscode · 56 tokens

auto-perf-optimize

Run agent-driven VS Code performance or memory investigations. Use when asked to launch Code OSS, automate a VS Code scenario, run the Chat memory smoke runner, capture renderer heap snapshots, take workflow screenshots, compare run summaries, or drive a repeatable scenario before heap-snapshot analysis.

microsoft/vscode · 62 tokens