103

Early Hints

1xx Informational

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Server perspective

Use 103 when you can safely send helpful headers, especially Link hints, before the final response is ready.

When to use

  • •Return 103 to advertise critical preload or preconnect work early
  • •Use it only for hints that remain sensible even before the final response arrives

How to respond

  • •Send the early hint headers first, then follow with the normal final response
  • •Keep the hints consistent with the eventual page or representation

Headers to consider

  • •Link
  • •Content-Security-Policy

Response body

  • •Do not include a response body in a 103 response

Server-side pitfalls

  • •Do not expose sensitive or misleading hints before the final response is known
  • •Do not overuse preloads that waste bandwidth or contention on the client

Examples

Preloading a critical script

Request:GET /app
Response:103 Early Hints with Link headers, then 200 OK with HTML

The server helps the browser begin fetching critical assets before the final payload arrives.

References

Related 1xx Informational Codes

100

Continue

The server is saying, 'I checked the start of your request. It looks okay so far, so go ahead and send the big part now.'

101

Switching Protocols

The server is saying, 'Let's keep talking, but switch to a different protocol for the rest of this connection.'

102

Processing

The server is saying, 'I’m still working on this. Don’t assume the request was lost just because it’s taking a while.'

WebDAV