420 Enhance Your Calm / Method Failure

Two unrelated legacy meanings: rate limiting in the old Twitter API, and a failed method in early Spring versions.

Status

HTTP/1.1 420 Enhance Your Calm / Method Failure

Details

Category: 4xx
Status: Unofficial (Twitter API v1, Spring Framework). Not registered with IANA. A server, framework, or CDN convention.
Specification: none, not defined by any RFC
Cacheable: Not cacheable
Response body: Allowed
Retry: Retry after a delay

Twitter's version 1 API returned 420 Enhance Your Calm when a client exceeded its rate limit, a reference to the film Demolition Man. Later API versions replaced it with the standard 429.

Separately, older Spring Framework releases used 420 Method Failure as a Spring-specific error. Both meanings are obsolete, and any 420 in current traffic is coming from legacy software.

Common causes

A client hitting rate limits on an old Twitter API endpoint.
A legacy Spring application signalling an internal method failure.

How to fix it

As the client

Back off as you would for a 429 and reduce request rate.
Move to the current version of whichever API you are calling.

As the server

Use 429 for rate limiting. It is standard, documented, and understood by client libraries.

Examples

GET /1/statuses/user_timeline.json HTTP/1.1
Host: api.twitter.com

HTTP/1.1 420 Enhance Your Calm
Retry-After: 60