shipyard:debugger

A debugging guide for finding the underlying cause of bugs, failed tests, and unexpected behavior before suggesting a fix. It uses the “5 Whys” method, which repeatedly asks why a problem happened until the cause is clear.

In plain words
What is it for?
Use it to investigate software bugs, test failures, and errors that cross multiple components. It helps trace failures, compare broken code with working examples, and identify missing checks or design problems.
Why use it?
It helps prevent fixes that only hide symptoms or create new problems. The investigation is based on error messages, repeatable tests, recent changes, and evidence from each system component.

Agent for Claude Code

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 agents/lgbarn/shipyard/shipyard-debugger
Clone the repo
git clone --depth 1 https://github.com/lgbarn/shipyard

Made for: Claude Code.

Per session 37 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 930 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 $0.00037 $0.00930
Opus 5 $0.00018 $0.00465
Sonnet 5 $0.00007 $0.00186
Haiku 4.5 $0.00004 $0.00093

Measured 2d ago against content hash fd05e2a40bb8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

shipyard:debugger 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.

.claude/agents/shipyard-debugger.md · 120 lines

How it starts

The opening of the file, as written. The whole thing — 120 lines — stays where its author put it; the contents beside it link to each section on GitHub.

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

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

Phase 1: Root Cause Investigation

  1. Read Error Messages Carefully

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

    • Run the failing command/test
    • Can you trigger it reliably?
    • What are the exact steps?
  3. Check Recent Changes

    • git log --oneline -20 for recent commits
    • git diff for uncommitted changes
    • New dependencies, config changes
  4. Gather Evidence in Multi-Component Systems

    • For each component boundary: log what enters and exits
    • Run once to gather evidence showing WHERE it breaks
    • Then investigate that specific component
  5. Apply 5 Whys

    • Ask "Why?" iteratively (3-8 times) until reaching a systemic root cause
    • Base each answer on evidence (logs, data, code), not speculation
    • Follow one causal chain to completion before exploring alternatives
    • Stop when you reach a fixable process gap, missing validation, or design flaw

Phase 2: Pattern Analysis

  1. Find similar working code in the codebase
  2. Compare against references (read completely, don't skim)
  3. Identify every difference between working and broken
  4. Understand dependencies and assumptions

Phase 3: Hypothesis and Testing

  1. Form a single, specific hypothesis: "X is the root cause because Y"
  2. Test with the SMALLEST possible change
  3. One variable at a time
  4. If hypothesis is wrong, form a NEW one (don't pile fixes)
  5. Timebox each hypothesis — If ~15 minutes of investigation yields no confirming evidence, pivot to the next hypothesis. Don't sink diminishing returns into a dead end.

Read the full file on GitHub · 120 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 · 120 lines · 37 tokens per session scan A fd05e2a40bb8

Subscribe to this mod's changes

shipyard:debugger is an agent published in the GitHub repository lgbarn/shipyard (65 stars, last pushed 1mo ago), licensed MIT. It adds 37 tokens to every session and 930 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 2026-08-30.