# Cron Reference: Expressions, Options, MCP Reference for bunqueue scheduling: the five-field cron syntax and its shortcuts, every repeat option with defaults and per-SDK naming, and cron control from AI agents. Canonical: https://bunqueue.dev/guide/cron/reference/ ---
guide ยท cron jobs

Every field, every option.

The expression syntax with its shortcuts, the full repeat option table with defaults and the naming each SDK uses, plus managing schedules through an AI agent.

## Cron Expression Cheat Sheet Five fields, left to right: minute (0-59), hour (0-23), day of month (1-31), month (1-12), day of week (0-7; both 0 and 7 are Sunday). | Expression | Meaning | | -------------- | ------------------------ | | `0 9 * * *` | Every day at 9:00 AM | | `*/15 * * * *` | Every 15 minutes | | `0 0 * * MON` | Every Monday at midnight | | `0 0 1 * *` | First day of every month | Shortcuts (`@daily`, `@hourly`, `@weekly`, `@monthly`, `@yearly`, `@midnight`) and a six-field form with a leading seconds field are also accepted. The seconds field supports values `0-59`, `*`, lists, ranges and steps; for example, `0,30 * * * * *` runs twice per minute. The five calendar fields are evaluated by Bun's native cron parser. Seven-field expressions with a year and the non-POSIX `L`, `W`, `#`, `+`, and `?` modifiers are not supported. ### Time zones and daylight-saving transitions The five calendar fields follow Bun 1.4's native cron semantics in the selected IANA timezone. The leading-seconds adapter keeps the same calendar decision and then selects the requested second within that minute: - During spring-forward, a fixed time inside the missing hour moves forward by the DST gap (`02:30` runs at `03:30`). For a multi-minute pattern entirely inside the gap, only its first missing match fires after the jump. - During fall-back, a fixed time inside the repeated hour fires once, at the first occurrence. A pattern whose minute or hour field is `*` traverses both occurrences, once per matching real-time minute. These rules intentionally match Bun and Linux cron behavior. They differ from Croner for some wildcard patterns in a repeated fall-back hour. ## Scheduler Options Options on the repeat object of `upsertJobScheduler`: | Option | Default | Description | | --------------------- | ---------------------------------------- | ----------------------------------------------------------------------- | | `pattern` | - | Cron expression | | `every` | - | Positive safe-integer interval in ms (alternative to `pattern`) | | `timezone` | `UTC` (embedded) / server timezone (TCP) | IANA timezone for `pattern` evaluation | | `limit` | unlimited | Max executions, then the scheduler is removed | | `immediately` | `false` | Fire once right away on first creation | | `skipIfNoWorker` | `false` | Skip a run when no worker is registered for the queue | | `preventOverlap` | `true` | Skip a run while the previous job is still active | | `skipMissedOnRestart` | `true` | On server restart, recompute the next run instead of firing missed runs | ### SDK naming and availability | Semantic option | Bun | Node.js / Deno | Python | PHP | Go | Rust | Elixir | | ------------------- | --------------------- | --------------------- | ------------------------ | --------------------- | ------------------------------- | ------------------- | --------------------- | | cron pattern | `pattern` | `pattern` | `pattern` | `pattern` | `Pattern` | `pattern` | `pattern` | | interval | `every` | `every` | `every` | `every` | `EveryMs` | `every_ms` | `every` | | timezone | `timezone` | `tz` | `tz` | `tz` | `Timezone` | `timezone` | `tz` or `timezone` | | skip with no worker | `skipIfNoWorker` | `skipIfNoWorker` | `skip_if_no_worker` | `skipIfNoWorker` | `SkipIfNoWorker` | `skip_if_no_worker` | `skipIfNoWorker` | | missed-run policy | `skipMissedOnRestart` | `skipMissedOnRestart` | `skip_missed_on_restart` | `skipMissedOnRestart` | `SkipMissedOnRestart` (`*bool`) | server default only | `skipMissedOnRestart` | | overlap policy | `preventOverlap` | `preventOverlap` | `prevent_overlap` | `preventOverlap` | `PreventOverlap` (`*bool`) | server default only | `preventOverlap` | Rust's scheduler type currently omits `skipMissedOnRestart` and `preventOverlap`; both therefore use the server default `true`. Go uses pointer booleans for those two fields so explicit `false` is distinct from omission. `addCron` and `every` convenience helpers exist in TypeScript and Python only; PHP, Go, Rust, and Elixir use the scheduler API directly. At least one timing field is required. If both `pattern` and a valid `every` value are supplied, `pattern` takes precedence for backward compatibility. The server rejects non-numeric, non-finite, non-integer, unsafe, zero, and negative intervals before changing the existing scheduler definition. :::note[Fixed-rate and global identity] Scheduler `every` advances from its previous scheduled slot. It is not a delay after job completion. Scheduler IDs are also global to the broker, so prefix them when multiple applications or queues share one server. ::: ## AI Agents (MCP) AI agents can manage cron jobs in natural language ("create a cron that cleans old sessions every hour") through the [MCP Server](/guide/mcp/): ```bash bun add bunqueue @modelcontextprotocol/sdk claude mcp add bunqueue -- bunx --package=bunqueue bunqueue-mcp ``` :::tip[Related Guides] - [Queue API](/guide/queue/) - Job options for cron-created jobs - [CLI Commands](/guide/cli/) - Manage cron jobs via CLI - [MCP Server](/guide/mcp/) - AI agent integration ::: ## Where to go next | | | | --------------------------------------------------------- | --------------------------------------------------- | | [Job Schedulers from the Queue](/guide/queue/schedulers/) | Named repeatable schedules on the Queue object | | [Cron Jobs in Bun](/guide/cron/) | Your first schedule, in every SDK and from the CLI | | [Cron Recipes](/guide/cron/recipes/) | Fixed intervals, timezones, repeat-after-completion |