Web site: ZeroSSL

Available since acme4j 3.2.0

Connection URIs

  • acme:// - Production server

ZeroSSL does not provide a staging server (as of Feburary 2024).


  • ZeroSSL requires account creation with key identifier.
  • ZeroSSL makes use of the retry-after header, so expect that the fetch() methods return an Instant, and wait until this moment has passed (see example).
  • Certificate creation can take a considerable amount of time (up to 24h). The retry-after header still gives a short retry period, resulting in a very high number of status update reattempts.
  • Server response can be very slow sometimes. It is recommended to set a timeout of 30 seconds or higher in the network settings.


If you have used the example code of acme4j before version 3.2.0, please review the updated example for how to use ZeroSSL with acme4j.


acme4j is not officially supported or endorsed by ZeroSSL. If you have acme4j related issues, please do not ask them for support, but open an issue here.