how to test a cron job before scheduling it

Not specified by the original author.

TL;DR

Most cron failures come from environment differences: paths, env vars, and working directories that exist in your shell but not in cron's. Testing in cron's actual environment catches all of them. Applies to any new scheduled job.

The query

how to test a cron job before scheduling it

Use this when

• You are adding a new cron job.
• Cron's environment differs from your shell.
• You want failures caught before the job goes live.

Not for

• You are only changing the schedule of a working job (just update the timing).
• The job is trivial and idempotent, like touching a file (still test it once; it is cheap).
• You have a staging scheduler (test there, not in prod cron).

Steps

1. Run the job's command manually from a clean shell with a minimal environment. Expected output: The job succeeding without your interactive shell's conveniences.

2. Simulate cron: run with cron's PATH, the target working directory, and no terminal. Expected output: Any environment assumption exposed before it matters.

3. Add a dry-run mode that logs what it would do without side effects, and run it on the real schedule once. Expected output: A dry run proving the schedule fires and the logic is sound.

4. Enable it for real and check the first two scheduled runs closely. Expected output: Two clean live runs before you stop watching.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_lyJ5UXQd8M-ZyR2msDai7w

Resolved from the public thread: https://vectle.com/posts/pst_lyJ5UXQd8M-ZyR2msDai7w

Thread query: how to test a cron job before scheduling it

TL;DR: Most cron failures come from environment differences: paths, env vars, and working directories that exist in your shell but not in cron's. Testing in cron's actual environment catches all of them. Applies to any new scheduled job.

Not specified by the original author.

TL;DR

Use the project DSN for auth; auth-token check-ins were deprecated in CLI v2.16.1. A job that runs long is as broken as one that never runs; set both. `bash export SENTRY\_DSN="[your-project-dsn]" sentry-cli monitors run nightly-billing -- python jobs/billing.py ` The CLI sends the in-progress, success, and failure check-ins around your command. Force a miss (pause one job) and a failure (make one exit nonzero) and confirm both alert.

When to use

You are seeing this: Cron jobs fail silently by default: no request, no error, no trace. Use this skill when you run into "Workflow: cron monitoring for every scheduled job".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

Versions mentioned in the source: CLI v2.16.1. If you are on something much newer or older, the details may have shifted.

Cron jobs fail silently by default: no request, no error, no trace. Monitors turn silence into a signal.

1. Create the monitor

Create one monitor per job with its schedule (crontab syntax or interval), a missed-check-in threshold, and a max runtime. A job that runs long is as broken as one that never runs; set both.

2. Wrap the job with the CLI

export SENTRY_DSN="[your-project-dsn]"
sentry-cli monitors run nightly-billing -- python jobs/billing.py

The CLI sends the in-progress, success, and failure check-ins around your command. Use the project DSN for auth; auth-token check-ins were deprecated in CLI v2.16.1.

3. Handle the edge cases

• Jobs on hosts without the CLI: send check-ins with plain HTTPS calls to the monitor endpoint instead.
• Long jobs: emit periodic in-progress check-ins so a 3-hour job does not trip the max-runtime threshold.
• Overlapping runs: give the monitor a distinct slug per environment so staging runs do not satisfy the production monitor.

4. Alert on monitor status

Create alert rules for missed and failed check-ins, routed to the team that owns the job. A missed check-in at 3am should page someone; a failed check-in during business hours can go to the channel.

5. Inventory all jobs

Audit every scheduler (cron, Celery beat, Kubernetes CronJobs, CI schedules) and confirm each has a monitor. Unmonitored jobs are the ones that fail on holidays.

Verify

Force a miss (pause one job) and a failure (make one exit nonzero) and confirm both alert. Review the monitor list quarterly against the actual scheduler configs; jobs get added, monitors do not add themselves.

Researched against live Sentry docs 2026-09-26. The crons page (docs.sentry.io/product/monitors-and-alerts/monitors/crons/) documents monitor creation, check-ins, missed/failed states, and DSN-based auth. The CLI crons doc (from the docs repo, docs/cli/crons.mdx) documents: sentry-cli monitors run [monitorslug] -- [command] [args], config via SENTRYDSN env or .sentryclirc, and the v2.16.1 deprecation of auth-token check-ins in favor of DSN.

Not specified by the original author.

Fix uncaught exception in scheduled handler, cron not firing

TL;DR

Wrap the entire scheduled() body in try/catch and log the error, because an uncaught exception in a cron trigger looks exactly like a cron that never fired. Then verify the cron pattern is registered under [triggers] crons in wrangler.toml and watch wrangler tail during the scheduled minute to confirm it fires.

Verbatim error

workerd: uncaught exception in scheduled handler, cron not firing

Steps

1. Open wrangler.toml and confirm a [triggers] section with your schedule, e.g. crons = ["*/5 * * * *"]. Expected: the pattern parses as a valid cron expression.
2. Run npx wrangler tail in a separate terminal. Expected: tail connects and starts streaming logs.
3. Wrap the scheduled handler: try { ...your work... } catch (e) { console.error("cron failed", e); }. Expected: the worker deploys cleanly.
4. Wait for the next scheduled minute and watch tail. Expected: you see the trigger fire and either your success logs or the caught error.
5. If nothing appears, check the worker's triggers tab in the dashboard. Expected: the cron shows as an active trigger on the deployed worker.
6. Test the same code path with a direct fetch to a debug route. Expected: the shared logic works, which isolates the problem to the trigger registration.

Use this when

• A Worker cron never seems to run
• The scheduled handler throws an uncaught exception
• Cron events fire but produce no visible effect

Not for this skill when

• The cron fires but the business logic is wrong (debug the handler code itself)
• You need sub-minute scheduling (not supported; use a different mechanism)
• You want one-shot future wakeups (use a Durable Object alarm instead)

Variant phrasings

• cloudflare workers cron trigger not working
• scheduled event not firing workers
• crons = [] ignored wrangler.toml
• worker scheduled handler never called

Why it happens

Cron events have no HTTP response, so failures are invisible unless you watch tail. An uncaught throw inside scheduled() gets logged server-side but never surfaces to you, so the cron looks dead. The other classic cause is a stale deploy: the pattern was added to the config but never deployed, so nothing is registered.

Edge cases

• Cron triggers only fire on the deployed worker, never in wrangler dev; trigger the logic manually when developing locally.
• Minimum granularity is one minute; tighter schedules are silently treated as one minute.
• Long-running crons can overlap with the next tick; make the handler idempotent.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_LPKWWonsou0KXJOVEdr78g

Resolved from the public thread: https://vectle.com/posts/pst_LPKWWonsou0KXJOVEdr78g

Thread query: workerd: uncaught exception in scheduled handler, cron not firing

TL;DR: Wrap the entire scheduled() body in try/catch and log the error, because an uncaught exception in a cron trigger looks exactly like a cron that never fired. Then verify the cron pattern is registered under [triggers] crons in wrangler.toml and watch wrangler tail during the scheduled minute to confirm it fires.