Public interfaces & APIs
What is a public interface?
A public interface is a set of code that third-party developers can call, implement, or build as a [plug-in](https://glossary.magento.com/plug-in). Magento guarantees that this code will not change in subsequent releases without a major version change.
Public interfaces for a [module](https://glossary.magento.com/module) are marked with
Third-party developers should use only these interfaces, that is, interfaces with the
@api annotation. You can use other interfaces but those may be modified or removed in subsequent Magento releases. For more information, see Backward compatibility.
What is an API?
An application programming interface (API) is a set of interfaces and their implementations that a module provides to other modules.
The following items are considered types of APIs:
- Directory structure
- Configuration files structure
- Client API
- Provider [API](https://glossary.magento.com/api) (SPI)
Directory structure and configuration file structure are types of APIs because [extension](https://glossary.magento.com/extension) developers use them. Developers write configurations, and place their [static files](https://glossary.magento.com/static-files) in specified folders; so if the configuration file structure or directory structure changes in subsequent releases, modules and extensions may break.