HTTP 100 Continue — What It Means & How to Fix It

What Does This Error Mean?

HTTP 100 Continue is an informational response from the server telling the client it has received the request headers and the client may proceed to send the request body. This is a behind-the-scenes handshake — normal users never see a 100 response in their browser. 100 is not an error — it is a normal part of how large file uploads and form submissions work.

Affected Models

All web browsers
All web servers
REST APIs
Mobile apps
Desktop applications

Common Causes

Client sent an Expect: 100-continue header with a large upload request
Server is confirming it can accept the incoming data before the client sends the full body
API client is using chunked transfer encoding and waiting for server confirmation
Upload form or file submission tool is checking server readiness before sending
HTTP/1.1 multi-step request process for large payloads

How to Fix It

If you are a regular user and see HTTP 100 mentioned in an error message, simply refresh the page and try again.

Normal users should never encounter HTTP 100 directly — if you are seeing it, it may be displayed incorrectly by an application.
If you are uploading a large file and the upload appears to hang, check your internet connection stability.

HTTP 100 is part of the upload process — a slow connection may cause it to appear to stall.
If you are a developer, ensure your server sends the 100 Continue response before the client times out waiting for it.

The default wait time for many clients is 1–5 seconds — a slow server response can cause the client to abort.
If using an API client (like Postman or curl), add the --expect100-timeout flag or disable the Expect header if it is causing issues.

curl uses Expect: 100-continue by default for POST requests over 1024 bytes — disable with -H 'Expect:' if needed.
If your server does not support Expect: 100-continue, configure it to respond with 417 Expectation Failed instead.

This tells the client to resend the request without the Expect header so the transfer can proceed normally.
For persistent 100 Continue issues in a web app, check server and proxy logs to trace the full request lifecycle.

Load balancers and reverse proxies sometimes strip or mishandle the 100 Continue response.

When to Call a Professional

HTTP 100 is not an error and does not require professional intervention. If you are a developer and HTTP 100 is causing unexpected behavior, check that your server is correctly handling the Expect: 100-continue header. Most modern web frameworks handle this automatically.

Frequently Asked Questions

Is HTTP 100 an error code?

No — 100 Continue is an informational status code in the 1xx range. 1xx codes are not errors — they are interim responses during a multi-step process. The only HTTP codes that indicate problems are 4xx (client errors) and 5xx (server errors).

Will I ever see HTTP 100 in my browser?

Almost never — browsers handle 100 Continue internally and do not display it to users. You might see it in browser developer tools under the Network tab if you inspect a large file upload. If an application is displaying '100' as an error message, that is an app-level display bug.

What happens if the server sends a 100 Continue but the client already sent the body?

In practice, clients often send the body immediately without waiting for 100 Continue. If the server sends 100 after the body is already received, it is simply ignored. HTTP 100 is an optional optimization — not a required step in every request.