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

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API Endpoint

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GET /check

Checks if the specified URL is reachable and returns timing and status information.
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url
string
required
The target URL to check (must be http or https)

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Example Request

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

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Success Response (Reachable)

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status
string
Reachability status: "reachable" or "unreachable"
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responseTime
number
Round-trip response time in milliseconds
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statusCode
number
HTTP status code returned by the target server
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colo
string
Cloudflare edge data center (IATA code) that served this check (only available when deployed)
{
  "status": "reachable",
  "responseTime": 87,
  "statusCode": 200,
  "colo": "LHR"
}

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Success Response (Unreachable)

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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."
}

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Error Response

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

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Error Codes

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

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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

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Deployment

1

Click the deploy button

Deploy to Cloudflare Workers
2

Deploy

Follow the deployment wizard to deploy the Worker to your Cloudflare account. No additional configuration required.
3

Test your deployment

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

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Local Development

cd experiments/is-it-down
npm install
npm run dev
Test locally: 
curl "http://localhost:8787/check?url=https://www.cloudflare.com"
The colo field will not be populated during local development. It only appears when deployed to Cloudflare Workers.

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Cloudflare Features Used

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