Diagnose

Skill tyecode/skills/skills/engineering/diagnose

Personal AI agent skills for better coding. Fixes common agent failure modes: misaligned requirements, blind coding, debugging loops, and lost context between sessions.

Install

npx -y skills add tyecode/skills --skill diagnose

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One thing to look at

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What its author says it does

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Runs a disciplined diagnosis loop for hard bugs and performance regressions. Use when user says "diagnose this" / "debug this", reports a bug, or describes a performance regression.

SKILL.md

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Skill: diagnose

When to Use This Skill

Use this skill when:

User says "diagnose this" or "debug this"
Reports a bug, something is broken/throwing/failing
Describes a performance regression

The Diagnosis Loop (6 Phases)

Phase 1 — Build a feedback loop

Everything else is mechanical. If you have a fast, deterministic pass/fail signal for the bug, you will find the cause.

Ways to construct a loop (in order):

Failing test at the bug seam
Curl / HTTP script against dev server
CLI invocation with fixture input
Headless browser script (Playwright)
Throwaway harness - minimal subset of the system

A 2-second deterministic loop is a debugging superpower.

Phase 2 — Reproduce

Run the loop. Watch the bug appear.

Confirm the failure matches what user described
Confirm it's reproducible

Phase 3 — Hypothesise

Generate 3-5 ranked hypotheses before testing any.

Format: "If X is the cause, then changing Y will make the bug disappear"

Show the ranked list to the user - they often have domain knowledge.

Phase 4 — Instrument

Each probe must map to a specific prediction. Change one variable at a time.

Use debugger if available
Add targeted logs at boundaries
Tag all debug logs with [DEBUG-xxx] for easy cleanup

Phase 5 — Fix + regression test

Write the regression test before the fix:

Turn minimised repro into failing test
Watch it fail
Apply the fix
Watch it pass

Phase 6 — Cleanup

Original repro no longer reproduces
Regression test passes
All [DEBUG-...] instrumentation removed
Document what caused it in the commit message

Then ask: What would have prevented this bug?