Both indicate that the server cannot process the request right now, but the reasons differ.
Definition:
Indicates that the client has sent too many requests in a given timeframe.
Key Points:
- Related to rate limiting.
- The server is healthy, but the client is overloading it.
- Response may include
Retry-Afterheader to tell client when to retry.
Example Scenario:
- API allows 100 requests per minute.
- Client sends 120 requests in a minute → server responds 429 Too Many Requests.
Definition:
Indicates that the server is temporarily unable to handle the request, usually due to overload or maintenance.
Key Points:
- Related to server-side issues, not the client.
- Server may be down for maintenance, or overloaded.
- Response may include
Retry-Afterheader to indicate when service will be available.
Example Scenario:
- Web server is overloaded with traffic or undergoing maintenance → responds 503 Service Unavailable.
| Feature | 429 Too Many Requests | 503 Service Unavailable |
|---|---|---|
| Cause | Client sends too many requests | Server temporarily unavailable |
| Responsibility | Client-side (rate limiting) | Server-side (overload/maintenance) |
| Retry | Retry after specified time (Retry-After) |
Retry after server recovers |
| Example | API request limit exceeded | Server down for maintenance |
- 429: Like a restaurant telling a frequent customer, “You’ve ordered too many dishes too fast, wait a bit before ordering more.”
- 503: Like a restaurant telling everyone, “We are closed for cleaning or too crowded, come back later.”
💡 Key takeaway:
- 429 → Client is sending too much.
- 503 → Server is temporarily unavailable.