Is It Down?

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

API ReferenceCopy Anchor Link

GET /checkCopy Anchor Link

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

Example RequestCopy Anchor Link

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

Success Response (Reachable)Copy Anchor Link

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)Copy Anchor Link

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 ResponseCopy Anchor Link

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

Error CodesCopy Anchor Link

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

Use CasesCopy Anchor Link

• 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

LimitationsCopy Anchor Link

• 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

Use in your projectCopy Anchor Link

import { FETCH_TIMEOUT_MS } from "../constants/defaults";export interface FetchResult {  ok: boolean;  statusCode: number;  responseTimeMs: number;  error?: string;}/** * Fetches a URL and returns status and response time. * Uses AbortController for timeout. */export async function fetchWithTiming(url: string): Promise<FetchResult> {  const start = Date.now();  const controller = new AbortController();  const timeoutId = setTimeout(() => controller.abort(), FETCH_TIMEOUT_MS);  try {    const res = await fetch(url, {      method: "GET",      signal: controller.signal,      headers: { "User-Agent": "Cloudflare-Experiments-IsItDown/1.0" },    });    const responseTimeMs = Date.now() - start;    clearTimeout(timeoutId);    return {      ok: res.ok,      statusCode: res.status,      responseTimeMs,    };  } catch (e) {    clearTimeout(timeoutId);    const responseTimeMs = Date.now() - start;    const message = e instanceof Error ? e.message : "Unknown error";    return {      ok: false,      statusCode: 0,      responseTimeMs,      error: message,    };  }}

DeploymentCopy Anchor Link

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

Local DevelopmentCopy Anchor Link

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 UsedCopy Anchor Link

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