debugging

A method for finding software bugs by observing the failure, forming a possible explanation, and testing it with small experiments.

In plain words
What is it for?
Use it to investigate bugs, build a test that reliably reproduces a failure, compare possible causes, and narrow the problem until its source is isolated.
Why use it?
It prevents guesswork and premature fixes when something is failing. A focused test loop helps confirm the real cause and shows when the problem is fixed.

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/tslateman/duet/debugging
Any agent
npx skills add tslateman/duet --skill debugging
Clone the repo
git clone --depth 1 https://github.com/tslateman/duet

Made for: Claude Code, Codex.

Per session 48 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,359 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 $0.00048 $0.01359
Opus 5 $0.00024 $0.00679
Sonnet 5 $0.00010 $0.00272
Haiku 4.5 $0.00005 $0.00136

Measured yesterday against content hash ee3f167962d0, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

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/debugging/SKILL.md · 142 lines

How it starts

The opening of the file, as written. The whole thing — 142 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Systematic Debugging

Overview

Apply the scientific method to software failures. Observe before theorizing. Form hypotheses, design experiments, narrow the cause. Refuse to jump to fixes until the cause is isolated.

The Scientific Debugging Loop

  1. Observe, What exactly happens? What did you expect?
  2. Hypothesize, What could cause this specific discrepancy?
  3. Predict, If the hypothesis is true, what else must be true?
  4. Test, Design the smallest experiment that confirms or refutes
  5. Conclude, Update understanding, repeat from step 2 if refuted

Never skip from Observe to Fix. The loop exists because human intuition about bug causes is wrong more often than right.

Build the Loop First

For a hard bug, this is the skill, everything else is mechanical. Before you hypothesize, build a tight, red-capable feedback loop: one command that drives the actual bug path and goes red on this bug, green once fixed. With it, bisection, hypothesis-testing, and instrumentation all just consume it. Without it, no amount of staring at code will save you. Spend disproportionate effort here, be aggressive, be creative, refuse to give up. See references/feedback-loops.md for the ten ways to construct one, how to tighten it, and what to do with non-deterministic bugs.

Completion criterion, a loop that goes red. Do not proceed to hypotheses until you can name one command you have already run at least once (paste the invocation and its output) that is:

  • Red-capable, drives the real bug path and asserts the user's exact symptom; not "runs without erroring"
  • Deterministic, same verdict every run (flaky bugs: a pinned, high reproduction rate)
  • Fast, seconds, not minutes
  • Agent-runnable, runs unattended

If you catch yourself reading code to build a theory before this command exists, stop, jumping straight to a hypothesis is the exact failure this guards against. Then minimise: shrink the repro to the smallest scenario that still goes red, cutting one element at a time, so Phase 3's hypothesis space is small and the result becomes a clean regression test.

Read the full file on GitHub · 142 lines

Files

What ships with it

3 files 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. yesterday First seen · 142 lines · 48 tokens per session scan A ee3f167962d0

Subscribe to this mod's changes

debugging is a skill published in the GitHub repository tslateman/duet (1 stars, last pushed 4d ago), licensed MIT. It adds 48 tokens to every session and 1,359 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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