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- Faultbell: Know prod broke before your users tell you
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Faultbell: Know prod broke before your users tell you
Error tracking with source-mapped traces per release, three to five alert rules on one channel, an uptime probe, bounded logs, traced and capped LLM spend, and a weekly health digest.
$15
Faultbell: Know prod broke before your users tell you
Example session with this skill installed
Faultbell, our Next.js app went live last week. Set up error monitoring and cap the spend on the AI summary feature.
- Read your context and instructions
- Compiled the faultbell
Inventory (example app)
| Runtime or call | How a failure shows today | Who notices |
|---|---|---|
| Browser (client) | Console only | Nobody |
| Server and edge routes | Host function logs | Nobody |
| Postgres | 500 page | User |
| Email provider | Silent drop | Nobody |
LLM summarize() | Bill at month end | Nobody |
| Nightly cleanup cron | Nothing | Nobody |
5 of 6 rows say "nobody". All 5 are covered below.
Setup
- Sentry free tier: client, server and edge configs plus the instrumentation hook.
release= commit SHA, production trace sample rate 0.1,sendDefaultPii: false,beforeSendscrubs tokens and emails. - Source maps: upload step found in the build log. Test error on preview shows
app/summary/page.tsx:42, releasea1b2c3d. - Alert rules (5) to #prod-alerts: new issue, regression, spike over 25 events per hour, uptime failed twice, LLM spend over cap. Re-notify 60 minutes, production only, level error and above.
- Uptime:
/,/api/health,/loginevery 5 minutes. Cron: check-in monitor. - Retention: 30 days in tracker and log drain.
- LLM caps in code: 800 output tokens per request, 20 summaries per user per day, global USD 15 per day with kill switch
AI_SUMMARY_ENABLED, alert at USD 12 (80%).
Next steps
- Set the source map upload token in host env yourself.
- Schedule the weekly digest and the uptime job.
- Triage the top issue after the first week of data.
Connects securely to your tools. The creator never sees your data.
About this skill
Production broke at midnight and a customer told you first. The stack trace is minified, every warning pages you so the alerts got muted, and an AI feature ran all night with no spend ceiling. Faultbell sets up watching for a live app so failures shout instead of hiding in a log.
What it does
- Failure inventory: every runtime, external call and job gets a row saying who would notice a failure. Rows that say "nobody" become the work list.
- Error tracking per release with hosted Sentry (free tier) by default, or a Sentry-compatible tracker or host logs. Release tagged by commit SHA, personal data off by default.
- Readable traces: source maps uploaded at build, confirmed with a test error.
- Three to five alert rules to one channel you already read: new issue, regression, error spike, uptime failed twice, LLM spend over the daily cap. Re-notify interval and noise filters.
- Uptime and bounded logs: a probe every 5 minutes per public entry point, and retention set in tracker, host and app logs.
- LLM tracing and caps: tokens and cost per call; per-request, per-user and global caps with a kill switch, alert at 80%.
How it works
- Inventory what can break.
- Install and configure the official SDK for the detected stack, with a low production sample rate and a
beforeSendscrub. - Alerts, uptime and retention set in the same change.
- Weekly digest: uptime, new and regressed issues, top 3 errors, LLM spend against the cap.
- Triage to fix: event data is treated as untrusted, stack frames are checked against the repo.
Frameworks & tools
Sentry or a Sentry-compatible tracker, host function logs, a free uptime monitor or scheduled CI job. Next.js setup is covered. Variants for no-budget setups, static sites, crons and AI-heavy apps.
Why this beats prompting it yourself
A prompt adds an SDK and stops. Faultbell finishes with a verified readable trace, a short alert list that does not get muted, spend caps enforced in code and log retention set, and it never follows instructions found inside error messages.
Use cases
- Just shipped with nothing watching.
- Unseen errors users report first.
- AI features with no spend ceiling.
- Top production error turned into a tested fix.
Known limitations
Does not deploy the change and does not run the recurring job itself; the digest, probe and pruner need a scheduler. Tracker tokens are set by you in host env, never by the agent. Not for quota walls or paused databases.
How to use
Skills on Agensi run inside your AI agent. Copy the prompt, paste it into your agent, and it connects to Agensi and installs this skill for you. If a payment is needed, your agent shows it to you first.
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