HTTP 100 Continue vs 429 Too Many Requests
HTTP 100 (Continue) is a 1xx Informational response, while 429 (Too Many Requests) is a 4xx Client Error response. 100 indicates that the server has received the request headers and the client should proceed to send the request body. This lets the client know it can continue with the request or abort if the headers were rejected. In contrast, 429 means that the user has sent too many requests in a given time (rate limiting). The response should include a Retry-After header.
Description
The server has received the request headers and the client should proceed to send the request body. This lets the client know it can continue with the request or abort if the headers were rejected.
When You See It
When a client sends an Expect: 100-continue header, the server responds with 100 before the client sends the body.
How to Fix
This is an interim response — no fix needed. The client should continue sending the request body.
Description
The user has sent too many requests in a given time (rate limiting). The response should include a Retry-After header.
When You See It
When hitting API rate limits or making too many requests too quickly.
How to Fix
Check the Retry-After header. Implement exponential backoff. Consider caching responses.
Key Differences
100 is a 1xx Informational response, while 429 is a 4xx Client Error response.
HTTP 100: The server has received the request headers and the client should proceed to send the request body. This lets the client know it can continue with the request or abort if the headers were rejected.
HTTP 429: The user has sent too many requests in a given time (rate limiting). The response should include a Retry-After header.
You encounter 100 when when a client sends an Expect: 100-continue header, the server responds with 100 before the client sends the body.
You encounter 429 when when hitting API rate limits or making too many requests too quickly.
When to Use Which
For 100 (Continue): This is an interim response — no fix needed. The client should continue sending the request body. For 429 (Too Many Requests): Check the Retry-After header. Implement exponential backoff. Consider caching responses.