420 Method Failure or Enhance your calm
The HTTP response status code 420 Method Failure and 420 Enhance your calm is an unofficial client error that is returned by the server to indicate a client error. If it is sent by the Spring Framework then it indicates that a method has failed, whereas if it is sent by Twitter then it indicates that the client is being rate limited for making too many requests.
Usage – Twitter
In version 1.0 of the Twitter Search and Trends API, it used the 420 Enhance your calm error message to indicate that the client was being rate limited for making too many requests. The intention was to ease traffic by restricting clients to a certain number of requests within a specific time. With the release of Standard v1.1 of the Twitter API, this status has been deprecated, and instead, they use the official message 429 Too Many Requests.
Usage – Spring Framework
When the 420 Method Failure error message is sent by the Spring Framework, it indicates that a method has failed. However, this status code has been deprecated by Spring and is no longer used.
Note
Search engines like Google will not index a URL with 420 Method Failure or 420 Enhance your calm response status, and consequently, URLs that have been indexed in the past but are now returning this HTTP status code will be removed from the search results.
Code references
Apache HttpComponents Core
org.apache.hc.core5.http.HttpStatus.SC_METHOD_FAILURE
Takeaway
The 420 Method Failure and 420 Enhance your calm status code are client errors that were generated by the Spring Framework and Twitter Search. However, the use of this code has been deprecated by both of these platforms.