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Cloudflare Cron Triggers for scheduled Workers execution. Use for periodic tasks, scheduled jobs, or encountering handler not found, invalid cron expression, timezone errors.
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Cloudflare Cron Triggers for scheduled Workers execution. Use for periodic tasks, scheduled jobs, or encountering handler not found, invalid cron expression, timezone errors. 📦 Ships with claude-skills
</> SKILL.md
cloudflare-cron-triggers.SKILL.md
---
name : cloudflare-cron-triggers
description : "Cloudflare Cron Triggers for scheduled Workers execution. Use for periodic tasks, scheduled jobs, or encountering handler not found, invalid cron expression, timezone errors."
metadata:
keywords:
- cloudflare cron
- cron triggers
- scheduled workers
- scheduled handler
- periodic tasks
- background jobs
- scheduled tasks
- cron expression
- wrangler crons
- scheduled event
- green compute
- workflow triggers
- maintenance tasks
- scheduled() handler
- ScheduledController
- UTC timezone
license : MIT
---
# Cloudflare Cron Triggers
**Status**: Production Ready ✅
**Last Updated**: 2025-11-25
**Dependencies**: cloudflare-worker-base (for Worker setup)
**Latest Versions**: wrangler@4.50.0, @cloudflare/workers-types@4.20251125.0
---
## Quick Start (5 Minutes)
### 1. Add Scheduled Handler to Your Worker
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**src/index.ts:**
```typescript
export default {
async scheduled(
controller: ScheduledController,
env: Env,
ctx: ExecutionContext
): Promise<void> {
console.log('Cron job executed at:', new Date(controller.scheduledTime));
console.log('Triggered by cron:', controller.cron);
// Your scheduled task logic here
await doPeriodicTask(env);
},
};
```
**Why this matters:**
- Handler must be named exactly `scheduled` (not `scheduledHandler` or `onScheduled`)
- Must be exported in default export object
- Must use ES modules format (not Service Worker format)
### 2. Configure Cron Trigger in Wrangler
**wrangler.jsonc:**
```jsonc
{
"name": "my-scheduled-worker",
"main": "src/index.ts",
"compatibility_date": "2025-10-23",
"triggers": {
"crons": [
"0 * * * *" // Every hour at minute 0
]
}
}
```
**CRITICAL:**
- Cron expressions use 5 fields: `minute hour day-of-month month day-of-week`
- All times are **UTC only** (no timezone conversion)
- Changes take **up to 15 minutes** to propagate globally
### 3. Test Locally
```bash
# Enable scheduled testing
bunx wrangler dev --test-scheduled
# In another terminal, trigger the scheduled handler
curl "http://localhost:8787/__scheduled?cron=0+*+*+*+*"
# View output in wrangler dev terminal
```
**Testing tips:**
- `/__scheduled` endpoint is only available with `--test-scheduled` flag
- Can pass any cron expression in query parameter
- Python Workers use `/cdn-cgi/handler/scheduled` instead
### 4. Deploy
```bash
npm run deploy
# or
bunx wrangler deploy
```
**After deployment:**
- Changes may take up to 15 minutes to propagate
- Check dashboard: Workers & Pages > [Your Worker] > **Cron Triggers**
- View past executions in **Logs** tab
---
## When to Load References
**Load immediately when user mentions**:
- `cron-expressions-reference.md` → "cron syntax", "schedule format", "expression", "minute hour day", "every X minutes"
- `common-patterns.md` → "examples", "use cases", "patterns", "real-world", "database cleanup", "report generation", "how to"
- `integration-patterns.md` → "implement", "Hono", "multiple triggers", "bindings", "workflows", "error handling"
- `wrangler-config.md` → "configuration", "wrangler.jsonc", "multiple crons", "environment-specific", "dev staging production"
- `testing-guide.md` → "test", "local development", "__scheduled", "unit test", "curl", "debugging"
**Load proactively when**:
- Building new scheduled task → Load `integration-patterns.md`
- Configuring wrangler.jsonc → Load `wrangler-config.md`
- Debugging cron expression → Load `cron-expressions-reference.md`
- Testing locally → Load `testing-guide.md`
- Looking for examples → Load `common-patterns.md`
---
## Cron Expression Syntax
### Five-Field Format
```
* * * * *
│ │ │ │ │
│ │ │ │ └─── Day of Week (0-6, Sunday=0)
│ │ │ └───── Month (1-12)
│ │ └─────── Day of Month (1-31)
│ └───────── Hour (0-23)
└─────────── Minute (0-59)
```
### Special Characters
| Character | Meaning | Example |
|-----------|---------|---------|
| `*` | Every | `* * * * *` = every minute |
| `,` | List | `0,30 * * * *` = every hour at :00 and :30 |
| `-` | Range | `0 9-17 * * *` = every hour from 9am-5pm |
| `/` | Step | `*/15 * * * *` = every 15 minutes |
### Common Patterns
```bash
# Every minute
* * * * *
# Every 5 minutes
*/5 * * * *
# Every 15 minutes
*/15 * * * *
# Every hour at minute 0
0 * * * *
# Every hour at minute 30
30 * * * *
# Every 6 hours
0 */6 * * *
# Every day at midnight (00:00 UTC)
0 0 * * *
# Every day at noon (12:00 UTC)
0 12 * * *
# Every day at 3:30am UTC
30 3 * * *
# Every Monday at 9am UTC
0 9 * * 1
# Every weekday at 9am UTC
0 9 * * 1-5
# Every Sunday at midnight UTC
0 0 * * 0
# First day of every month at midnight UTC
0 0 1 * *
# Twice a day (6am and 6pm UTC)
0 6,18 * * *
# Every 30 minutes during business hours (9am-5pm UTC, weekdays)
*/30 9-17 * * 1-5
```
**CRITICAL: UTC Timezone Only**
- All cron triggers execute on **UTC time**
- No timezone conversion available
- Convert your local time to UTC manually
- Example: 9am PST = 5pm UTC (next day during DST)
---
## ScheduledController Interface
```typescript
interface ScheduledController {
readonly cron: string; // The cron expression that triggered this execution
readonly type: string; // Always "scheduled"
readonly scheduledTime: number; // Unix timestamp (ms) when scheduled
}
```
### Properties
#### `controller.cron` (string)
The cron expression that triggered this execution.
```typescript
export default {
async scheduled(controller: ScheduledController, env: Env): Promise<void> {
console.log(`Triggered by: ${controller.cron}`);
// Output: "Triggered by: 0 * * * *"
},
};
```
**Use case:** Differentiate between multiple cron schedules (see Multiple Cron Triggers pattern).
#### `controller.type` (string)
Always returns `"scheduled"` for cron-triggered executions.
```typescript
if (controller.type === 'scheduled') {
// This is a cron-triggered execution
}
```
#### `controller.scheduledTime` (number)
Unix timestamp (milliseconds since epoch) when this execution was scheduled to run.
```typescript
export default {
async scheduled(controller: ScheduledController): Promise<void> {
const scheduledDate = new Date(controller.scheduledTime);
console.log(`Scheduled for: ${scheduledDate.toISOString()}`);
// Output: "Scheduled for: 2025-10-23T15:00:00.000Z"
},
};
```
**Note:** This is the **scheduled** time, not the actual execution time. Due to system load, actual execution may be slightly delayed (usually <1 second).
---
## Execution Context
```typescript
export default {
async scheduled(
controller: ScheduledController,
env: Env,
ctx: ExecutionContext // ← Execution context
): Promise<void> {
// Use ctx.waitUntil() for async operations that should complete
ctx.waitUntil(logToAnalytics(env));
},
};
```
### `ctx.waitUntil(promise: Promise<any>)`
Extends the execution context to wait for async operations to complete after the handler returns.
**Use cases:**
- Logging to external services
- Analytics tracking
- Cleanup operations
- Non-critical background tasks
```typescript
export default {
async scheduled(controller: ScheduledController, env: Env, ctx: ExecutionContext): Promise<void> {
// Critical task - must complete before handler exits
await processData(env);
// Non-critical tasks - can complete in background
ctx.waitUntil(sendMetrics(env));
ctx.waitUntil(cleanupOldData(env));
ctx.waitUntil(notifySlack({ message: 'Cron completed' }));
},
};
```
**Important:** First `waitUntil()` that fails will be reported as the status in dashboard logs.
---
## Integration Patterns
**6 production-ready cron patterns**:
1. **Standalone Worker with Cron** - Single scheduled function for background tasks (database cleanup, report generation)
2. **Hono + Cron Combination** - HTTP endpoints + scheduled tasks in one Worker, sharing bindings and reducing costs
3. **Multiple Cron Triggers** - Different schedules for different tasks using `controller.cron` to route execution
4. **Accessing Bindings** - Use D1, KV, R2, AI, Vectorize, Queues, Workflows, Durable Objects in scheduled functions
5. **Integrating with Workflows** - Trigger complex, long-running multi-step workflows on schedule
6. **Error Handling Best Practices** - Comprehensive error handling with retry logic, alerting (Slack/email), failure logging, and monitoring
**Load `references/integration-patterns.md` for complete implementations with code examples, configuration details, and best practices.**
---
## Wrangler Configuration
Add cron triggers to `wrangler.jsonc` in the `triggers.crons` array. Each trigger requires a `cron` expression. Supports multiple crons (Free: 3 max, Paid: higher limits) and environment-specific configurations for dev/staging/production deployments.
**Load `references/wrangler-config.md` for complete configuration examples including multiple triggers, environment-specific schedules, timezone handling, and removal procedures.**
---
## Testing & Development
Test scheduled functions locally using the `/__scheduled` endpoint by running `bunx wrangler dev --test-scheduled`, then triggering handlers with `curl "http://localhost:8787/__scheduled?cron=0+*+*+*+*"` (use `+` instead of spaces in cron expressions).
**Load `references/testing-guide.md` for complete testing strategies, local development setup, unit testing examples, integration testing patterns, and production monitoring techniques.**
---
## Green Compute
Run cron triggers only in data centers powered by renewable energy.
### Enable Green Compute
**Via Dashboard:**
1. Go to [Workers & Pages](https://dash.cloudflare.com/?to=/:account/workers-and-pages)
2. In **Account details** section, find **Compute Setting**
3. Click **Change**
4. Select **Green Compute**
5. Click **Confirm**
**Applies to:**
- All cron triggers in your account
- Reduces carbon footprint
- No additional cost
- May introduce slight delays in some regions
**How it works:**
- Cloudflare routes cron executions to green-powered data centers
- Uses renewable energy: wind, solar, hydroelectric
- Verified through Power Purchase Agreements (PPAs) and Renewable Energy Credits (RECs)
---
## Known Issues Prevention
This skill prevents **6** documented issues:
### Issue #1: Cron Changes Not Propagating
**Error:** Cron triggers updated in wrangler.jsonc but not executing
**Source:** [Cloudflare Docs - Cron Triggers](https://developers.cloudflare.com/workers/configuration/cron-triggers/)
**Why It Happens:**
- Changes to cron triggers take up to **15 minutes** to propagate globally
- Cloudflare network needs time to update edge nodes
- No instant propagation like regular deploys
**Prevention:**
- Wait 15 minutes after deploy before expecting execution
- Check dashboard: Workers & Pages > [Worker] > Cron Triggers
- Use `wrangler triggers deploy` for trigger-only changes
```bash
# If you only changed triggers (not code), use:
bunx wrangler triggers deploy
# Wait 15 minutes, then verify in dashboard
```
---
### Issue #2: Handler Does Not Export
**Error:** `Handler does not export a 'scheduled' method`
**Source:** Common deployment error
**Why It Happens:**
- Handler not named exactly `scheduled`
- Handler not exported in default export object
- Using Service Worker format instead of ES modules
**Prevention:**
```typescript
// ❌ Wrong: Incorrect handler name
export default {
async scheduledHandler(controller, env, ctx) { }
};
// ❌ Wrong: Not in default export
export async function scheduled(controller, env, ctx) { }
// ✅ Correct: Named 'scheduled' in default export
export default {
async scheduled(controller, env, ctx) { }
};
```
---
### Issue #3: UTC Timezone Confusion
**Error:** Cron runs at wrong time
**Source:** User expectation vs. reality
**Why It Happens:**
- All cron triggers run on **UTC time only**
- No timezone conversion available
- Users expect local timezone
**Prevention:**
Convert your local time to UTC manually:
```typescript
// Want to run at 9am PST (UTC-8)?
// 9am PST = 5pm UTC (17:00)
{
"triggers": {
"crons": ["0 17 * * *"] // 9am PST = 5pm UTC
}
}
// Want to run at 6pm EST (UTC-5)?
// 6pm EST = 11pm UTC (23:00)
{
"triggers": {
"crons": ["0 23 * * *"] // 6pm EST = 11pm UTC
}
}
// Remember: DST changes affect conversion!
// PST is UTC-8, PDT is UTC-7
```
**Tools:**
- [Time Zone Converter](https://www.timeanddate.com/worldclock/converter.html)
- [Cron Expression Generator](https://crontab.guru/)
---
### Issue #4: Invalid Cron Expression
**Error:** Cron doesn't execute, no error shown
**Source:** Silent validation failure
**Why It Happens:**
- Invalid cron syntax silently fails
- Validation happens at deploy, but may not be obvious
- Common mistakes: wrong field order, invalid ranges
**Prevention:**
```bash
# ❌ Wrong: Too many fields (6 fields instead of 5)
"crons": ["0 0 * * * *"] # Has seconds field - not supported
# ❌ Wrong: Invalid minute range
"crons": ["65 * * * *"] # Minute must be 0-59
# ❌ Wrong: Invalid day of week
"crons": ["0 0 * * 7"] # Day of week is 0-6 (use 0 for Sunday)
# ✅ Correct: 5 fields, valid ranges
"crons": ["0 0 * * 0"] # Sunday at midnight UTC
```
**Validation:**
- Use [Crontab Guru](https://crontab.guru/) to validate expressions
- Check wrangler deploy output for errors
- Test locally with `--test-scheduled`
---
### Issue #5: Missing ES Modules Format
**Error:** `Worker must use ES modules format`
**Source:** Legacy Service Worker format
**Why It Happens:**
- Scheduled handler requires ES modules format
- Old Service Worker format not supported
- Mixed format in codebase
**Prevention:**
```typescript
// ❌ Wrong: Service Worker format
addEventListener('scheduled', (event) => {
event.waitUntil(handleScheduled(event));
});
// ✅ Correct: ES modules format
export default {
async scheduled(controller, env, ctx) {
await handleScheduled(controller, env, ctx);
},
};
```
---
### Issue #6: CPU Time Limits Exceeded
**Error:** `CPU time limit exceeded`
**Source:** Long-running scheduled tasks
**Why It Happens:**
- Default CPU limit: 30 seconds
- Long-running tasks exceed limit
- No automatic timeout extension
**Prevention:**
**Option 1: Increase CPU limit in wrangler.jsonc**
```jsonc
{
"limits": {
"cpu_ms": 300000 // 5 minutes (max for Standard plan)
}
}
```
**Option 2: Use Workflows for long-running tasks**
```typescript
// Instead of long task in cron:
export default {
async scheduled(controller, env, ctx) {
// Trigger Workflow that can run for hours
await env.MY_WORKFLOW.create({
params: { task: 'long-running-job' },
});
},
};
```
**Option 3: Break into smaller chunks**
```typescript
export default {
async scheduled(controller, env, ctx) {
// Process in batches
const batch = await getNextBatch(env.DB);
for (const item of batch) {
await processItem(item);
}
// If more work, send to Queue for next batch
const hasMore = await hasMoreWork(env.DB);
if (hasMore) {
await env.MY_QUEUE.send({ type: 'continue-processing' });
}
},
};
```
---
## Always Do ✅
1. **Use exact handler name** - Must be `scheduled`, not `scheduledHandler` or variants
2. **Use ES modules format** - Export in default object, not addEventListener
3. **Convert to UTC** - All cron times are UTC, convert from local timezone
4. **Wait 15 minutes** - Cron changes take up to 15 min to propagate
5. **Test locally first** - Use `wrangler dev --test-scheduled`
6. **Validate cron syntax** - Use [Crontab Guru](https://crontab.guru/)
7. **Handle errors gracefully** - Log, alert, and optionally re-throw
8. **Use ctx.waitUntil()** - For non-critical async operations
9. **Consider Workflows** - For tasks that need >30 seconds CPU time
10. **Monitor executions** - Check dashboard logs regularly
---
## Never Do ❌
1. **Never assume local timezone** - All crons run on UTC
2. **Never use 6-field cron expressions** - Cloudflare uses 5-field format (no seconds)
3. **Never rely on instant propagation** - Changes take up to 15 minutes
4. **Never use Service Worker format** - Must use ES modules format
5. **Never forget error handling** - Uncaught errors fail silently
6. **Never run CPU-intensive tasks without limit increase** - Default 30s limit
7. **Never use day-of-week 7** - Use 0 for Sunday (0-6 range only)
8. **Never deploy without testing** - Always test with `--test-scheduled` first
9. **Never ignore execution logs** - Dashboard shows past failures
10. **Never hardcode schedules for testing** - Use environment-specific configs
---
## Common Use Cases
**Load `references/common-patterns.md` for 10 real-world cron patterns including database cleanup, API data collection, daily reports generation, cache warming, monitoring & health checks, data synchronization, backup automation, sitemap generation, webhook processing, and scheduled notifications.**
---
## TypeScript Types
```typescript
// Scheduled event controller
interface ScheduledController {
readonly cron: string;
readonly type: string;
readonly scheduledTime: number;
}
// Execution context
interface ExecutionContext {
waitUntil(promise: Promise<any>): void;
passThroughOnException(): void;
}
// Scheduled handler
export default {
async scheduled(
controller: ScheduledController,
env: Env,
ctx: ExecutionContext
): Promise<void>;
}
```
---
## Limits & Pricing
### Limits
| Feature | Free Plan | Paid Plan |
|---------|-----------|-----------|
| **Cron triggers per Worker** | 3 | Higher (check docs) |
| **CPU time per execution** | 10 ms (avg) | 30 seconds (default), 5 min (max) |
| **Wall clock time** | 30 seconds | 15 minutes |
| **Memory** | 128 MB | 128 MB |
### Pricing
Cron triggers use **Standard Workers pricing**:
- **Workers Paid Plan**: $5/month required
- **Requests**: $0.30 per million requests (after 10M free)
- **CPU Time**: $0.02 per million CPU-ms (after 30M free)
**Cron execution = 1 request**
**Example:**
- Cron runs every hour (24 times/day)
- 30 days × 24 executions = 720 executions/month
- Average 50ms CPU time per execution
**Cost:**
- Requests: 720 (well under 10M free)
- CPU time: 720 × 50ms = 36,000ms (under 30M free)
- **Total: $5/month (just subscription)**
**High frequency example:**
- Cron runs every minute (1440 times/day)
- 30 days × 1440 = 43,200 executions/month
- Still under free tier limits
- **Total: $5/month**
---
## Troubleshooting
### Issue: Cron not executing
**Possible causes:**
1. Changes not propagated yet (wait 15 minutes)
2. Invalid cron expression
3. Handler not exported correctly
4. Worker not deployed
**Solution:**
```bash
# Re-deploy
bunx wrangler deploy
# Wait 15 minutes
# Check dashboard
# Workers & Pages > [Worker] > Cron Triggers
# Check logs
# Workers & Pages > [Worker] > Logs > Real-time Logs
```
---
### Issue: Handler executes but fails
**Possible causes:**
1. Uncaught error in handler
2. CPU time limit exceeded
3. Missing environment bindings
4. Network timeout
**Solution:**
```typescript
export default {
async scheduled(controller, env, ctx) {
try {
await yourTask(env);
} catch (error) {
// Log detailed error
console.error('Handler failed:', {
error: error.message,
stack: error.stack,
cron: controller.cron,
time: new Date(controller.scheduledTime),
});
// Send alert
ctx.waitUntil(sendAlert(error));
// Re-throw to mark as failed
throw error;
}
},
};
```
Check logs in dashboard for error details.
---
### Issue: Wrong execution time
**Cause:** UTC vs. local timezone confusion
**Solution:**
Convert your desired local time to UTC:
```typescript
// Want 9am PST (UTC-8)?
// 9am PST = 5pm UTC (17:00)
{
"triggers": {
"crons": ["0 17 * * *"]
}
}
```
**Tools:**
- [World Clock Converter](https://www.timeanddate.com/worldclock/converter.html)
- Remember DST changes (PST vs PDT)
---
### Issue: Local testing not working
**Possible causes:**
1. Missing `--test-scheduled` flag
2. Wrong endpoint (should be `/__scheduled`)
3. Python Worker (use `/cdn-cgi/handler/scheduled`)
**Solution:**
```bash
# Correct: Start with flag
bunx wrangler dev --test-scheduled
# In another terminal
curl "http://localhost:8787/__scheduled?cron=0+*+*+*+*"
```
---
## Production Checklist
Before deploying cron triggers to production:
- [ ] Cron expression validated on [Crontab Guru](https://crontab.guru/)
- [ ] Handler named exactly `scheduled` in default export
- [ ] ES modules format used (not Service Worker)
- [ ] Local timezone converted to UTC
- [ ] Error handling implemented with logging
- [ ] Alerts configured for failures
- [ ] CPU limits increased if needed (`limits.cpu_ms`)
- [ ] Environment bindings tested
- [ ] Tested locally with `--test-scheduled`
- [ ] Deployment tested in staging environment
- [ ] Waited 15 minutes after deploy for propagation
- [ ] Verified execution in dashboard logs
- [ ] Monitoring and alerting configured
- [ ] Documentation updated with schedule details
---
## Related Documentation
- **Cloudflare Cron Triggers**: https://developers.cloudflare.com/workers/configuration/cron-triggers/
- **Scheduled Handler API**: https://developers.cloudflare.com/workers/runtime-apis/handlers/scheduled/
- **Cron Trigger Examples**: https://developers.cloudflare.com/workers/examples/cron-trigger/
- **Multiple Cron Triggers**: https://developers.cloudflare.com/workers/examples/multiple-cron-triggers/
- **Wrangler Triggers Command**: https://developers.cloudflare.com/workers/wrangler/commands/#triggers
- **Workers Pricing**: https://developers.cloudflare.com/workers/platform/pricing/
- **Workflows Integration**: https://developers.cloudflare.com/workflows/
- **Crontab Guru** (validator): https://crontab.guru/
- **Time Zone Converter**: https://www.timeanddate.com/worldclock/converter.html
---
**Last Updated**: 2025-10-23
**Version**: 1.0.0
**Maintainer**: Claude Skills Maintainers | maintainers@example.com
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