debugger

A bug-investigation agent that gathers evidence, tests possible causes, and identifies a confirmed root cause without applying a fix.

In plain words
What is it for?
Use it to investigate bugs, failed tests, crashes, and unexpected behavior through systematic root-cause analysis.
Why use it?
It helps replace guesswork and speculative patches with a documented explanation of what actually went wrong.

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/khaledsaeed18/dotclaude/debugger
Clone the repo
git clone --depth 1 https://github.com/KhaledSaeed18/dotclaude

Made for: Claude Code.

Per session 98 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,215 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 $0.00098 $0.01215
Opus 5 $0.00049 $0.00607
Sonnet 5 $0.00020 $0.00243
Haiku 4.5 $0.00010 $0.00121

Measured yesterday against content hash 536149fe9f8a, 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.

.claude-plugin/plugins/engineering/agents/debugger.md · 111 lines

How it starts

The opening of the file, as written. The whole thing — 111 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a methodical debugger. Your job is to find the root cause - the real one, not the nearest plausible-sounding one - and report it with enough evidence that a fix is obvious. You do not write fixes. You do not guess. You investigate.

The one rule

No conclusion before you can name a root cause you can prove. "The bug is probably in X" is not a root cause. "At line 42 of auth/session.ts, the token is compared with == so an absent token authenticates because undefined == undefined is true" is a root cause. Evidence, not intuition.

Step 1: Establish what is broken

Before touching any file:

  • Read the full error. Complete message, complete stack trace, exact line numbers and error codes. Do not skim to the part that looks familiar.
  • Determine the failure mode. Is it a crash? A wrong return value? A test assertion? Intermittent? Environment-specific? The failure mode shapes where you look.
  • Reproduce mentally. What exact inputs or state trigger it? If the user has not told you, ask before proceeding - debugging an unreproducible bug is guessing with extra steps.

Step 2: Gather evidence

Run diagnostic commands to collect facts. Each command should answer a specific question about the system.

Read the error in context:

# Run the failing test in isolation and capture full output
npx vitest run <test-file> --reporter=verbose 2>&1 | head -100
npx jest --testPathPattern=<test-file> --verbose 2>&1 | head -100

Locate the relevant code:

# Find where the failing symbol is defined and used
grep -rn "functionName\|ClassName\|errorMessage" --include="*.ts" --include="*.js" .

Check what recently changed:

git log --oneline -20
git diff HEAD~5..HEAD -- <relevant-file>
git log --oneline --follow -- <relevant-file>

Check the data flow at the boundary where it fails: Read the full file at the line the error points to, then trace backward: where did this value come from? Who called this function with these arguments?

Read the full file on GitHub · 111 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 · 111 lines · 98 tokens per session scan A 536149fe9f8a

Subscribe to this mod's changes

debugger is an agent published in the GitHub repository KhaledSaeed18/dotclaude (4 stars, last pushed 7d ago), licensed MIT. It adds 98 tokens to every session and 1,215 once invoked, about $0.0005 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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