loom-debugging

loom-debugging is a skill for Claude Code from cosmix/loom. It costs 24 tokens per session (3,332 once invoked), scanned A, original, MIT.

A step-by-step method for finding and fixing software bugs, failed tests, data problems, and performance issues. It focuses on reproducing a failure, narrowing it down, identifying its root cause, and checking the fix.

In plain words
What is it for?
Investigating stack traces, flaky tests, regressions, crashes, data-quality issues, slow systems, and failures that occur in continuous integration but not on a developer’s machine.
Why use it?
It helps prevent symptom-patching, where a change hides the visible error but leaves the underlying problem in place.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

Good fit Investigating stack traces, flaky tests, regressions, crashes, data-quality issues, slow systems, and failures that occur in continuous integration but not on a developer’s machine.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/cosmix/loom/loom-debugging
View source ↗ cosmix/loom
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.

Any agent
npx skills add cosmix/loom --skill loom-debugging
Clone the repo
git clone --depth 1 https://github.com/cosmix/loom

Made for: Claude Code.

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 loom-debugging

README.md
[![agentmods](https://agentmods.dev/badge/skills/cosmix/loom/loom-debugging/github.svg)](https://agentmods.dev/skills/cosmix/loom/loom-debugging)
Your own site
<a href="https://agentmods.dev/skills/cosmix/loom/loom-debugging"><img src="https://agentmods.dev/badge/skills/cosmix/loom/loom-debugging/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 loom-debugging

Your own site · 80×15
<a href="https://agentmods.dev/skills/cosmix/loom/loom-debugging"><img src="https://agentmods.dev/badge/skills/cosmix/loom/loom-debugging.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 24 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,332 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
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 $0.00024 $0.03332
Opus 5.5 $0.00010 $0.01333
Sonnet 5.5 $0.00005 $0.00666
Haiku 4.5 $0.00002 $0.00333

Measured 1mo ago against content hash c71aea981c2a, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

loom-debugging scanned grade A with 1 finding 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 1mo 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

tcpdump -i any port 8080 # wire-level; curl -v for HTTP
skills/loom-debugging/SKILL.md · 232 lines

How it starts

The opening of the file, as written. The whole thing — 232 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Debugging

Overview

Find the true cause of a defect and prevent its recurrence — across app code, tests, data pipelines, ML, and infra. The failure mode to avoid is symptom-patching: changing code until the symptom disappears without understanding why, which moves the bug rather than fixing it.

The Root-Cause Loop

Run this loop; don't skip steps. Most wasted time comes from hypothesizing before reproducing, or fixing before localizing.

  1. Reproduce — deterministically. If you can't reproduce it, you can't verify a fix. Capture exact inputs, env, versions, and the full error/stack. For intermittent bugs, first make it more frequent (loop it, add load, shrink timeouts) before anything else.
  2. Minimize — shrink to the smallest input/code that still fails. Delete half, re-run, repeat (delta-debugging). A 5-line repro localizes faster than a 5000-line one and often reveals the cause outright.
  3. Localize — bound where it happens before asking why. Bisect in space (comment out / binary-search modules) and in time (git bisect). Read the stack trace top frame first, then the first frame in your code.
  4. Hypothesize — state a specific, falsifiable cause ("X is null because Y returns None when Z"). Vague hypotheses ("something with async") aren't testable.
  5. Test the hypothesis — one variable at a time; change something that should confirm/refute it. If the experiment can't distinguish two causes, design a better one.
  6. Fix — the root cause, minimally. Verify the repro now passes AND that you understand why the fix works (else you may have masked it).
  7. Prevent — add a regression test that fails without the fix. No regression test = the bug is not done. Then generalize: are there sibling instances of the same class elsewhere?

Core Discipline

  • Reproduce before fixing. Never "fix" what you can't observe failing.
  • Read the error fully — message, type, and every stack frame. The answer is often literally in it (wrong frame, unexpected value, swallowed cause).
  • Check recent changes. Most new failures are recently introduced → git log, git bisect.
  • Question your assumptions. The bug lives in what you're sure is correct. Verify it (print it, assert it) rather than believing it.
  • Preserve evidence. Save the failing input, logs, core dump, and seed before you start mutating code.

Read the full file on GitHub · 232 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. 1mo ago Changed · -33 tokens per session c71aea981c2a
  2. 1mo ago First seen · 232 lines · 57 tokens per session scan A 75b2248e8b1e

Subscribe to this mod's changes

loom-debugging is a skill published in the GitHub repository cosmix/loom (62 stars, last pushed today), licensed MIT. It adds 24 tokens to every session and 3,332 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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