Is It Down?

Check whether any website is reachable from Cloudflare's edge, with response time, status code, and edge location information.

API Reference

GET /check

Checks if the specified URL is reachable and returns timing and status information.

Example Request

curl "https://your-worker.workers.dev/check?url=https://www.cloudflare.com"

Success Response (Reachable)

status string

Reachability status: "reachable" or "unreachable"

responseTime number

Round-trip response time in milliseconds

statusCode number

HTTP status code returned by the target server

colo string

Cloudflare edge data center (IATA code) that served this check (only available when deployed)

{
  "status": "reachable",
  "responseTime": 87,
  "statusCode": 200,
  "colo": "LHR"
}

Success Response (Unreachable)

error string

Error message explaining why the site is unreachable (only present when status is "unreachable")

{
  "status": "unreachable",
  "responseTime": 5000,
  "statusCode": 0,
  "colo": "SFO",
  "error": "The operation was aborted."
}

Error Response

{
  "error": "Missing or invalid query parameter: url",
  "code": "INVALID_URL"
}

Error Codes

• 400 - Missing or invalid url parameter (not http/https)

Use Cases

• Monitor website availability from the edge
• Measure response times from different geographic locations
• Build uptime monitoring tools
• Check if a site is down globally or just from your location

Limitations

• Checks from the edge colo serving the request, not from every region globally
• Fetch timeout may mark slow but reachable sites as down
• HTTP reachability only; no SSL certificate or DNS health checks

Deployment

curl "https://your-worker.workers.dev/check?url=https://example.com"

Local Development

cd apps/experiments/is-it-down
npm install
npm run dev

Test locally:

curl "http://localhost:8787/check?url=https://www.cloudflare.com"

Cloudflare Features Used

• Workers - Edge compute runtime
• Fetch API - HTTP requests with timing
• Edge network - Request metadata including data center location