debug-investigate

A root-cause debugging method that reproduces a problem, tests possible explanations, traces the relevant code, verifies the cause, and then fixes it.

In plain words
What is it for?
Use it to reproduce bugs, investigate test or runtime failures, assess recent changes, and verify a fix. If the problem cannot be reproduced, it reports that instead of guessing.
Why use it?
It prevents premature fixes by requiring evidence that the suspected cause is actually responsible for the failure.

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/ccevans/bobbycode/bobby-debug
Any agent
npx skills add ccevans/bobbycode --skill bobby-debug
Clone the repo
git clone --depth 1 https://github.com/ccevans/bobbycode

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 1,257 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 $0.01257
Opus 5 $0.00024 $0.00629
Sonnet 5 $0.00010 $0.00251
Haiku 4.5 $0.00005 $0.00126

Measured yesterday against content hash 89a36cb3961f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

debug-investigate 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.

.claude/skills/bobby-debug/SKILL.md · 128 lines

How it starts

The opening of the file, as written. The whole thing — 128 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Bobby Debug Skill

Systematic root-cause debugging. Reproduce → Hypothesize → Trace → Verify → Fix. Never guess — follow the evidence.

Before Starting

  1. Check learnings — Read .claude/skills/bobby-debug/learnings.md + .claude/skills/bobby-debug/learnings.local.md
  2. Read the ticket's ticket.md — understand the expected vs actual behavior
  3. Read rejection comments — understand what was tried and what failed
  4. Run git log --oneline -10 to see recent changes

Investigation Methodology

<investigation_rules> Follow this process strictly. Do not skip steps or jump to fixes.

Step 1: Reproduce

  • Reproduce the failure with the exact steps from the rejection comment or bug report
  • If it's a test failure: run the specific test and capture the full output
  • If it's a runtime failure: trigger the exact flow and capture error output
  • If you cannot reproduce the bug, STOP. Report that the bug is not reproducible with the given steps.

Step 2: Hypothesize

  • Based on the error output and code path, form 1-3 hypotheses about the root cause
  • Write them down explicitly before investigating:
    • H1: "{description of what might be wrong}"
    • H2: "{alternative explanation}"
    • H3: "{less likely but possible cause}"

Step 3: Trace

  • For each hypothesis, trace the data flow through the code:
    • Read the entry point (API route, event handler, test setup)
    • Follow the call chain to where the error occurs
    • Check variable values, types, and state at each step
    • Use targeted console.log / print / debugger statements if needed (remove before committing)
  • Read files in parallel when tracing multiple hypotheses

Step 4: Verify

  • Identify which hypothesis is correct based on tracing evidence
  • Confirm by finding the exact line(s) where the bug manifests
  • Document: "Root cause: {specific explanation with file:line references}"

Step 5: Fix

  • Write the minimal fix that addresses the root cause
  • Write or update a test that would catch this regression
  • Run the full test suite: npm test
  • Run lint: npm run lint </investigation_rules>

Read the full file on GitHub · 128 lines

Files

What ships with it

2 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 · 128 lines · 48 tokens per session scan A 89a36cb3961f

Subscribe to this mod's changes

debug-investigate is a skill published in the GitHub repository ccevans/bobbycode (6 stars, last pushed 7d ago), licensed MIT. It adds 48 tokens to every session and 1,257 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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