All Certbot components including acme, Certbot, and non-third party plugins follow Semantic Versioning both for its Python API and for the application itself. This means that we will not change behavior in a backwards incompatible way except in a new major version of the project.
None of this applies to the behavior of Certbot distribution mechanisms such as our snaps or OS packages whose behavior may change at any time. Semantic versioning only applies to the common Certbot components that are installed by various distribution methods.
For Certbot as an application, the command line interface and non-interactive behavior can be considered stable with two exceptions. The first is that no aspects of Certbot’s console or log output should be considered stable and it may change at any time. The second is that Certbot’s behavior should only be considered stable with certain files but not all. Files with which users should expect Certbot to maintain its current behavior with are:
$domainis the certificate name (see Where are my certificates? for more details)
Hook directories in
Certbot’s behavior with other files may change at any point.
Another area where Certbot should not be considered stable is its behavior when not run in non-interactive mode which also may change at any point.
In general, if we’re making a change that we expect will break some users, we will bump the major version and will have warned about it in a prior release when possible. For our Python API, we will issue warnings using Python’s warning module. For application level changes, we will print and log warning messages.