HTTP 100 Continue — Meaning, Causes & How to Fix

Code

100

Name

Continue

Class

1xx Informational

Specification

RFC 9110 §15.2.1

Cacheable by default

Not applicable (interim response)

What HTTP 100 means

100 Continue is an interim response. A client that sends Expect: 100-continue with a large request body waits for it before uploading the body, so the server can reject the request (for example with 413 or 401) without the client wasting bandwidth. A final status code always follows.

Common causes

• The client sent Expect: 100-continue (curl does this automatically for larger POST/PUT bodies).
• Large file uploads through HTTP clients that negotiate before sending the body.

How to fix it

For site owners

• Nothing to fix — most web servers and frameworks answer 100 Continue automatically.
• If uploads hang, check that a proxy or load balancer in front of the app passes the interim response through.

For visitors & developers

• If a server never answers 100, clients normally send the body after a short timeout anyway.
• To skip the extra round trip in curl, send an empty header: -H "Expect:".

SEO impact

No SEO impact. Search engine crawlers fetch pages with GET requests and only act on the final status code of the response.

Example 100 response

HTTP/1.1 100 Continue

HTTP/1.1 201 Created
Location: /uploads/7f3a
Content-Length: 0

Related status codes

Check or look up another code

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