Retrofit is a type-safe HTTP client library developed by Square that enables developers to build REST API clients for Android and Java applications. The library provides a declarative approach to defining HTTP requests through Java interfaces, allowing developers to specify endpoints, request methods, parameters, and response types using annotations rather than writing boilerplate networking code. This annotation-driven design ensures compile-time type safety and reduces runtime errors when working with remote APIs.
The library is distributed through Maven Central under the coordinates com.squareup.retrofit2:retrofit:3.0.0, with development snapshots available from Sonatype's snapshots repository. Retrofit requires a minimum of Java 8 or Android API 21 to function. The project includes built-in support for R8 shrinking and obfuscation, with rules automatically included for users of that tool. ProGuard users must manually configure obfuscation rules from the retrofit2.pro file, and may also need to add rules for OkHttp, which serves as a dependency of the library.
According to GitGenius activity tracking, Retrofit maintains an active development and support cycle with a median issue and pull request response latency of 1.5 hours across 122 tracked items, though the mean response time extends to 697.5 hours, indicating some variance in handling different types of requests. The most frequently applied issue labels are Needs Info with 10 occurrences, Feature with 5 occurrences, and PR welcome with 5 occurrences, reflecting the project's engagement with community contributions and feature requests. Jake Wharton emerges as the dominant contributor and triager with 292 tracked events, followed by mhousser with 11 events and Goooler with 10 events, demonstrating concentrated maintainership.
The library's architecture supports asynchronous HTTP calls and integrates with various serialization converters, enabling seamless conversion between HTTP responses and Java objects. This makes it particularly valuable for Android development where network operations must be non-blocking, and for JVM applications requiring efficient API communication. The type-safe design means that API contracts are enforced at compile time rather than runtime, catching many integration errors before code execution.
Retrofit's influence extends across the broader Java ecosystem, as evidenced by overlapping contributors with other significant projects including pingcap/tidb, apache/pulsar, and material-components/material-components-android. This cross-project involvement suggests that Retrofit's design patterns and approaches have influenced HTTP client implementations and networking strategies in other major open-source initiatives. The library is licensed under the Apache License 2.0, making it freely available for both open-source and commercial use. Since its initial development in 2013, Retrofit has become a foundational tool in the Android development community and remains actively maintained with regular updates and community engagement.
