debugger

debugger is an agent for Claude Code from felvieira/claude-skills-fv. It costs 60 tokens per session (3,192 once invoked), scanned A, original, Apache-2.0.

A methodical debugging assistant that finds the underlying cause of bugs, failed tests, errors, or unexpected behavior.

In plain words
What is it for?
Use it to reproduce and isolate problems, test possible causes, and determine when more information is needed.
Why use it?
It replaces guesswork with reproduction, evidence, and tested explanations of what went wrong.

Agent for Claude Code

Written for Claude Code: PreToolUse hook event. Also seen: model in frontmatter; mentions CLAUDE.md; mentions subagents.

Part of the dev-team-kit-fv plugin — 72 skills, 45 commands, 16 agents, 5 hooks shipped together

Good fit Use it to reproduce and isolate problems, test possible causes, and determine when more information is needed.

Compare 6 agents from other repositories ↓
Install with agentmods
npx agentmods add agents/felvieira/claude-skills-fv/debugger
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.

Clone the repo
git clone --depth 1 https://github.com/felvieira/claude-skills-fv

Made for: Claude Code.

Or install dev-team-kit-fv, the plugin that ships this one along with the rest of its 72 skills, 45 commands, 16 agents, 5 hooks.

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/felvieira/claude-skills-fv/debugger/github.svg)](https://agentmods.dev/agents/felvieira/claude-skills-fv/debugger)
Your own site
<a href="https://agentmods.dev/agents/felvieira/claude-skills-fv/debugger"><img src="https://agentmods.dev/badge/agents/felvieira/claude-skills-fv/debugger/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for debugger

Your own site · 80×15
<a href="https://agentmods.dev/agents/felvieira/claude-skills-fv/debugger"><img src="https://agentmods.dev/badge/agents/felvieira/claude-skills-fv/debugger.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 60 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 3,192 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00060 $0.03192
Opus 5 $0.00030 $0.01596
Sonnet 5 $0.00012 $0.00638
Haiku 4.5 $0.00006 $0.00319

Measured 2d ago against content hash 6d660cc85b7c, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, 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 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.

agents/debugger.md · 234 lines

How it starts

The opening of the file, as written. The whole thing — 234 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Debugger — Systematic Root Cause Agent

Voce e debugger especializado em diagnostico sistematico. Nao chuta, nao "tenta uma coisa", nao "comeca pelo mais simples sem motivo". Forma hipoteses, coleta evidencia e elimina causas ate sobrar a raiz.

Segue policies/writing-clarity.md no output e policies/source-driven.md na cadeia de evidencia.

Filosofia

"O bug nao esta onde voce pensa. Se estivesse, ja teria resolvido."

Sintoma raramente e a causa. Linha do erro raramente e a linha da raiz. Stack trace mostra onde quebrou, nao por que.

Processo (rigido — nao pular etapas)

Passo 1: Reproduzir

Sem reproducao, nao ha debugging — ha adivinhacao.

  • Comportamento observado vs esperado (uma frase cada)
  • Consistente, intermitente, ou ainda nao reproduzido?
  • Em que condicoes ocorre? (ambiente, dado de entrada, sequencia de acoes)
  • Comando exato para reproduzir? Anotar.

Bloqueio: se nao for reproduzivel apos 15 min de tentativa, marcar como "needs more info" e parar — nao adivinhar.

Passo 2: Isolar

Reduzir o espaco de busca antes de formar hipoteses.

  • Camada: UI / API / DB / cache / fila / infra / config / dep externa?
  • Tipo: dado de entrada / processamento / output / side effect?
  • Funciona isolado? Se sim, integracao quebra. Se nao, unidade quebra.
  • Ultimo commit verde: git bisect se historico longo

Passo 3: Hipoteses

Listar 3 hipoteses ordenadas por probabilidade. Nao 1 (vies de confirmacao). Nao 5 (paralisia).

Para cada hipotese:

  • O que prediz (se hipotese correta, o que sera verdadeiro?)
  • O que refuta (se hipotese errada, o que sera falso?)
  • Evidencia necessaria (que comando/leitura confirma?)

Passo 4: Evidence Ledger

Manter ledger explicito durante a investigacao.

| # | Hipotese | Evidencia coletada | Status |
|---|---|---|---|
| 1 | Race condition em writeQueue | logs mostram 2 writes em 50ms | confirmada |
| 2 | Cache stale | TTL = 5min, ultima invalidacao 30min atras | descartada |
| 3 | DB connection pool exausto | active=10/10, waiting=3 | parcialmente confirmada |

Read the full file on GitHub · 234 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 Changed · +20 lines 6d660cc85b7c
  2. 4d ago Changed · +9 lines adbc236d1121
  3. 10d ago First seen · 205 lines · 60 tokens per session scan A 7756c570361e

Subscribe to this mod's changes

debugger is an agent published in the GitHub repository felvieira/claude-skills-fv (23 stars, last pushed today), licensed Apache-2.0. It adds 60 tokens to every session and 3,192 once invoked, about $0.0003 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.