100 Continue
The server has received the initial part of the request (the headers) and the client should continue sending the rest of the request body. If the request is already complete, this response can be safely ignored. It's an intermediate response — the server is saying "so far so good, keep going."
What can I do?
- No action needed — this is an informational or success response, not an error.
How to debug & fix
- Use Expect: 100-continue for large uploads to check server acceptance before sending the full body
- Handle 100 as an intermediate response and wait for the final 2xx/4xx/5xx
- Not normally seen in browsers — only in raw HTTP clients or APIs
- Verify your HTTP client library handles 100 Continue before sending large bodies.
Code Example
// Express: 100 Continue is handled automatically by Node.js HTTP module
// Client side: send Expect header
fetch(url, {
method: 'POST',
headers: { 'Expect': '100-continue' },
body: largeData
});Related Status Codes
How HTTP Status Codes Work
Every HTTP response carries a three-digit status code that tells the client — browser, API consumer, or search-engine crawler — exactly what happened. The first digit defines the class: 1xx informational (request in progress), 2xx success, 3xx redirection, 4xx client error (bad request, missing auth, not found), and 5xx server failure.
Status codes are standardised in RFC 9110 (HTTP Semantics, 2022). Extensions like WebDAV (RFC 4918) and rate-limit headers (RFC 6585) added codes beyond the core set. When a client receives an unrecognised code, the rule is to treat it as the generic x00 of its class.
Why the Right Code Matters
Semantically correct codes help search engines index accurately (301 passes link equity; 410 removes pages faster than 404), allow API clients to implement correct retry logic (429 + Retry-After, 503 + Retry-After), and let monitoring systems distinguish bugs (500) from load issues (503) from auth failures (401/403).
Looking up a different status code? The full reference covers all HTTP codes with causes, fix guides, and copyable code examples for Node.js and Python.
Browse the full HTTP Status Code reference →