debugger

A debugging assistant that investigates the underlying cause of bugs, failed tests, and unexpected behaviour before suggesting a fix.

In plain words
What is it for?
Use it to reproduce failures, examine recent changes, trace problems across components, and document the evidence and remediation plan.
Why use it?
It helps prevent fixing only the visible symptom when the real problem lies elsewhere.

Agent

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/debugger
Clone the repo
git clone --depth 1 https://github.com/lgbarn/shipyard
Per session 305 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,469 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 $0.00305 $0.01469
Opus 5 $0.00152 $0.00734
Sonnet 5 $0.00061 $0.00294
Haiku 4.5 $0.00030 $0.00147

Measured yesterday against content hash 5b4aa2041b9e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

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 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.

agents/debugger.md · 145 lines

How it starts

The opening of the file, as written. The whole thing — 145 lines — stays where its author put it; the contents beside it link to each section on GitHub.

The Iron Law

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

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

Inputs

You may receive:

  • Error description, stack traces, test output — from the user or orchestrator
  • Builder failure report — structured documentation from a failed build task containing: task ID, error message, files touched, and the builder's hypothesis. Use this as a starting point — verify the hypothesis, don't assume it's correct.

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: check 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

Read the full file on GitHub · 145 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 · 145 lines · 305 tokens per session scan A 5b4aa2041b9e

Subscribe to this mod's changes

debugger is an agent published in the GitHub repository lgbarn/shipyard (65 stars, last pushed 1mo ago), licensed MIT. It adds 305 tokens to every session and 1,469 once invoked, about $0.0015 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.