# CRN0

> CRN0 (https://crn0.com) converts cron expressions between timezones. It is DST-aware, explains schedules in plain English and lists the next run times. It is free, needs no auth, and offers an MCP server and a JSON API for agents.

Use CRN0 when a schedule is written for one timezone (e.g. "9am Sydney on weekdays") but runs on a machine or scheduler set to another timezone (usually UTC: GitHub Actions, AWS EventBridge, Kubernetes CronJobs, Vercel, Cloudflare).

Key facts for agents:
- Cron format: 5 fields (minute hour day-of-month month day-of-week). Names (JAN, MON), macros (@daily, @hourly...), and * , - / ? are supported. Seconds, year, L, W and # are not.
- A converted schedule can need more than one cron line (e.g. "every 15 min, 9am-5pm" across a day boundary). Use every returned line.
- Conversions use the UTC offsets that apply on the reference date. If either zone observes DST, the converted cron drifts by an hour for part of the year. Fixed-offset schedulers can't avoid this, so the result includes a `dstNote`.
- Timezone inputs accept IANA ids, abbreviations (PST, AEST, IST), offsets (UTC+8) or city names.

## Agent interfaces

- [MCP server](https://crn0.com/mcp): Streamable HTTP endpoint with no auth. Tools: convert_cron, describe_cron, next_cron_runs, search_timezones
- [JSON API: convert](https://crn0.com/api/convert?cron=0+9+*+*+1-5&from=Australia/Sydney&to=UTC): GET or POST. Params: cron, from, to, at?, count?
- [JSON API: describe](https://crn0.com/api/describe?cron=*/15+9-17+*+*+1-5): plain-English explanation and expanded fields
- [JSON API: next runs](https://crn0.com/api/next-runs?cron=0+0+*+*+*&timezone=America/New_York&count=5): upcoming run times
- [JSON API: timezone search](https://crn0.com/api/timezones?query=melbourne): resolves a city or abbreviation to an IANA id
- [OpenAPI spec](https://crn0.com/openapi.json): OpenAPI 3.1 description of the JSON API
- [Agent docs page](https://crn0.com/agents): setup instructions for Claude, Cursor, VS Code and other MCP clients

## Human pages

- [Converter](https://crn0.com/): interactive converter. Deep link: https://crn0.com/?cron=<cron>&from=<IANA>&to=<IANA>
- [Timezone index](https://crn0.com/timezones): every supported timezone with offsets and DST rules
- Pair pages, for example [UTC to EST](https://crn0.com/utc-to-est), [UTC to PST](https://crn0.com/utc-to-pst), [UTC to CST](https://crn0.com/utc-to-cst), [UTC to MST](https://crn0.com/utc-to-mst). Pattern: https://crn0.com/<from>-to-<to> using the slugs in llms-full.txt

## Optional

- [Full reference](https://crn0.com/llms-full.txt): tool schemas, API examples and every timezone slug
- [Sitemap](https://crn0.com/sitemap.xml)