Bolt api

CORS Preflight Request Timeout - OPTIONS Request Failing

POST or other non-simple requests fail because the CORS preflight OPTIONS request times out. Browser doesn't even send the actual request.

Requests work in some browsers but not others, or fail intermittently.

Error Messages You Might See

OPTIONS request timeout Preflight request failed No 'Access-Control-Allow-Methods' header CORS preflight failed
OPTIONS request timeoutPreflight request failedNo 'Access-Control-Allow-Methods' headerCORS preflight failed

Common Causes

  1. Server doesn't handle OPTIONS method
  2. OPTIONS request takes too long to respond
  3. Firewall blocking OPTIONS method
  4. CORS headers missing in OPTIONS response
  5. Preflight cache too short, requesting too frequently

How to Fix It

Ensure server responds to OPTIONS: if(request.method === 'OPTIONS') return new Response(null, { status: 200, headers: corsHeaders })

Response must include CORS headers: 'Access-Control-Allow-Methods', 'Access-Control-Allow-Headers', 'Access-Control-Max-Age'

Set long max-age: 'Access-Control-Max-Age': '86400' (24 hours)

Use middleware to add CORS to all routes

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Frequently Asked Questions

What is preflight?

Browser sends OPTIONS request to check if server allows cross-origin request. Server responds with allowed methods/headers

How long should preflight cache?

Access-Control-Max-Age: 86400 (24 hours). Longer is better - fewer OPTIONS requests

Which requests need preflight?

Non-simple: PUT, DELETE, POST with custom headers. Simple: GET, HEAD, POST with form-data

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