meteor-debugging

A step-by-step method for finding the cause of failures in Meteor 3 applications before changing code.

In plain words
What is it for?
Investigating crashes, browser-only errors, stuck data subscriptions, WebSocket or DDP disconnects, mismatched data, flaky tests, slow builds, and similar unexplained problems.
Why use it?
It helps separate problems in the browser, server, live data connections, builds, and tests so fixes target the actual failure instead of guessing.

Skill for Claude CodeCodex

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

Made for: Claude Code, Codex.

Per session 133 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,778 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 $0.00133 $0.01778
Opus 5 $0.00067 $0.00889
Sonnet 5 $0.00027 $0.00356
Haiku 4.5 $0.00013 $0.00178

Measured 2d ago against content hash 635445c11e7f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

meteor-debugging 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.

skills/meteor-debugging/SKILL.md · 145 lines

How it starts

The opening of the file, as written. The whole thing — 145 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Debug Meteor applications

Find the first failing boundary before changing behavior. Produce a stable reproduction, evidence for one cause, and a verification target. Then use the skill that owns the repair.

Diagnosis loop

  1. Record the exact symptom, complete error and stack, command or user action, Meteor release, resolved Atmosphere and npm versions, environment, and last known working state.
  2. Reproduce with the narrowest stable command or action before editing.
  3. Classify the first uncertain boundary with the table below.
  4. Read existing evidence before adding instrumentation. Compare client and server output, recent changes, and passing versus failing environments.
  5. Add one targeted observation only when current evidence cannot answer the question. Do not combine a diagnostic change with a speculative fix.
  6. State one falsifiable hypothesis and the observation that would reject it.
  7. Change one variable, reproduce, and trace a bad value or event backward to its origin.
  8. Fix the confirmed cause through the owning skill. Add a regression at the lowest reliable layer when the failure can recur.
  9. Re-run the focused reproduction, then the affected suite or production-like check. Remove temporary diagnostics and artifacts.

If several evidence-backed hypotheses fail, revisit the boundary map and assumptions before stacking mitigations or widening the change.

Select the boundary

Symptom First evidence Read
Build stalls, compilation error, rebuild regression, Rspack or SWC failure Full build output, --verbose, exact release and build-package versions Build debugging
Server crashes before startup or fails in a method, publication, job, or hook Earliest server stack, startup order, request-correlated evidence Runtime and inspector
Client stack, stale render, reactive loop, or client/server disagreement Browser stack, rendered state, reactive invalidation, server comparison Runtime and inspector, then the React or Blaze skill
Missing documents, stuck subscription, reconnect, or proxy/WebSocket symptom Server query, publication output, DDP state, subscription readiness, Minimongo DDP and data
Current output cannot distinguish an entry, guard, branch, state change, or event order A small set of redacted boundary observations Logs and instrumentation
Meteor Mocha failure, suite-only failure, async flake, or browser E2E failure Full hook output, client/server test counts, existing report and trace Tests and browser
Cordova or HCP problem, device-only failure, or live incident Device logs and versions; deployment logs, health, metrics, release diff Mobile and production

Read the full file on GitHub · 145 lines

Files

What ships with it

7 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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 First seen · 145 lines · 133 tokens per session scan A 635445c11e7f

Subscribe to this mod's changes

meteor-debugging is a skill published in the GitHub repository meteor/agent-skills (7 stars, last pushed 6d ago), licensed MIT. It adds 133 tokens to every session and 1,778 once invoked, about $0.0007 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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