HTTP 100 Continue

The server has received the request headers and the client should proceed to send the request body.

What 100 means

HTTP 100 Continue is an interim response indicating that the client should continue sending the request body. This is used when the client sends an Expect: 100-continue header, allowing the server to reject the request before the full body is transmitted — saving bandwidth.

Common causes

• Client sent Expect: 100-continue header
• Large file uploads where pre-validation is needed
• API requests with large payloads

How to fix it

• This is normal behaviour — no fix needed
• If you see this unexpectedly, check your HTTP client library settings

SEO impact

No direct SEO impact. This is an interim response that browsers handle automatically.

Monitoring tip

LemWatch tracks the final response code, not interim 1xx responses. If uploads are failing after a 100 Continue, check your server timeout settings.