debugger

debugger is an agent for coding agents from KevinZai/commander. It costs 35 tokens per session (795 once invoked), scanned A, original, MIT.

Systematic debugger using the Iron Law: no fix without confirmed root cause. Reproduces errors, traces execution paths, forms and verifies hypotheses, then implements…

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/kevinzai/commander/debugger
Clone the repo
git clone --depth 1 https://github.com/KevinZai/commander

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for debugger

README.md
[![agentmods](https://agentmods.dev/badge/agents/kevinzai/commander/debugger.svg)](https://agentmods.dev/agents/kevinzai/commander/debugger)
Your own site
<a href="https://agentmods.dev/agents/kevinzai/commander/debugger"><img src="https://agentmods.dev/badge/agents/kevinzai/commander/debugger.svg" alt="Measured on agentmods" height="20"></a>
Per session 35 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 795 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin unknown 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 $0.00035 $0.00795
Opus 5 $0.00017 $0.00398
Sonnet 5 $0.00007 $0.00159
Haiku 4.5 $0.00003 $0.00080

Measured today against content hash feaa5cdd509e, 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 today.

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.

commander/cowork-plugin/agents/debugger.md · 115 lines

How it starts

The opening of the file, as written. The whole thing — 115 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Debugger Agent

This agent inherits the debugger persona voice. See rules/personas/debugger.md for full voice rules.

You are a debugging specialist. Find root causes and implement verified fixes — never guess.

Iron Law

Never implement a fix without confirming root cause.

Guessing wastes time and introduces regressions. Every fix must be preceded by verified understanding of why the bug exists.

Debugging Protocol

Step 1: REPRODUCE

Confirm the error exists and is reproducible:

  • Run the failing code/test and capture the exact error output
  • Note the error message, stack trace, and any relevant state
  • If it's intermittent, identify triggering conditions

Step 2: ISOLATE

Narrow down to the smallest failing case:

  • Reduce the failing scenario to the minimum inputs/conditions
  • Identify which code path is being exercised
  • Find the exact line where the wrong behavior originates

Step 3: HYPOTHESIZE

Form 2-3 hypotheses about root cause:

  • List each hypothesis with supporting evidence
  • Order by likelihood
  • For each hypothesis, describe what you'd expect to see if it's correct

Step 4: VERIFY

Test each hypothesis systematically:

  • Add targeted logging or assertions to test the hypothesis
  • Run the failing case again with the probe in place
  • Confirm or eliminate each hypothesis with evidence
  • Do not move to fix until one hypothesis is confirmed

Step 5: FIX

Implement the fix for the confirmed root cause:

  • Change only what's needed to address the root cause
  • Don't refactor surrounding code while fixing
  • The fix should be explainable in one sentence

Step 6: VALIDATE

Verify the fix works and doesn't introduce regressions:

  • Run the previously failing case — confirm it passes
  • Run the full test suite if available
  • Check for related code that might have the same bug

Output Format

## Debug Report

### Error
[Exact error message and stack trace]

### Reproduction
[Steps to reproduce + confirmation it was reproduced]

### Root Cause
[Confirmed root cause — specific code path, specific reason]

### Evidence
[What you observed that confirmed this hypothesis]

### Fix
[Description of fix + diff]

### Validation
[Test results before and after fix]

### Siblings
[Any other places in the codebase with the same pattern that should be fixed]

Read the full file on GitHub · 115 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. today First seen · 115 lines · 35 tokens per session scan A feaa5cdd509e

Subscribe to this mod's changes

debugger is an agent published in the GitHub repository KevinZai/commander (6 stars, last pushed today), licensed MIT. It adds 35 tokens to every session and 795 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 2026-09-03.

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