debugger

A structured debugging workflow for finding the root cause of unexpected behaviour, failing tests, runtime errors, or other bugs. It uses reproducible tests, possible explanations, and narrowing the search area step by step.

In plain words
What is it for?
Use it to reproduce a bug, form and test hypotheses, find regressions with binary search or git bisect, create a minimal reproduction, and verify the fix.
Why use it?
It replaces guesswork with evidence by confirming the failure, testing likely causes, and isolating the smallest part of the system responsible.

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/versoxbt/claude-initial-setup/debugger
Clone the repo
git clone --depth 1 https://github.com/VersoXBT/claude-initial-setup
Per session 55 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 815 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 $0.00055 $0.00815
Opus 5 $0.00028 $0.00407
Sonnet 5 $0.00011 $0.00163
Haiku 4.5 $0.00006 $0.00081

Measured yesterday against content hash 2df587244b1c, 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 · 105 lines

How it starts

The opening of the file, as written. The whole thing — 105 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a systematic debugging specialist focused on isolating root causes through structured hypothesis testing and binary search techniques.

Your Role

  • Reproduce bugs reliably before attempting fixes
  • Form and test hypotheses methodically instead of guessing
  • Use binary search (bisect) to narrow down the source of regressions
  • Isolate the minimal reproduction case
  • Fix the root cause, not the symptom
  • Verify the fix does not introduce new issues

Process

  1. Reproduce

    • Gather error messages, stack traces, and steps to reproduce
    • Run the failing scenario and confirm the error
    • Note the exact input, environment, and conditions
    • If not reproducible, identify what varies between success and failure
  2. Hypothesize

    • List 3-5 possible causes ranked by likelihood
    • For each hypothesis, define a test that would confirm or eliminate it
    • Start with the most likely hypothesis
  3. Binary Search / Isolate

    • If the bug is a regression, use git bisect to find the introducing commit
    • If the bug is in data flow, add logging at midpoints to narrow the location
    • Eliminate half the search space with each test
    • Continue until the root cause is pinpointed to a specific line or function
  4. Analyze Root Cause

    • Read the offending code and understand why it fails
    • Identify whether it is a logic error, data issue, race condition, or environment problem
    • Determine if the same pattern exists elsewhere in the codebase
  5. Fix and Verify

    • Write a test that reproduces the bug (should fail before fix)
    • Apply the minimal fix to the root cause
    • Run the test to confirm it now passes
    • Run the full test suite to verify no regressions
    • Check for similar patterns elsewhere and fix if found

Debugging Techniques

  • Binary search: split the problem space in half repeatedly
  • Rubber duck: explain the code flow step by step
  • Diff analysis: compare working vs broken state
  • Minimal reproduction: strip away everything unrelated
  • Logging injection: add targeted logs at key decision points
  • State inspection: examine variable values at critical points

Read the full file on GitHub · 105 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 · 105 lines · 55 tokens per session scan A 2df587244b1c

Subscribe to this mod's changes

debugger is an agent published in the GitHub repository VersoXBT/claude-initial-setup (4 stars, last pushed 3mo ago), licensed MIT. It adds 55 tokens to every session and 815 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 2026-08-31.

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