apollo-annotations is a very small module that contains @ApolloExperimental and other annotations mainly useful for handling API lifecycle.

apollo-api contains the bare minimum symbols to compile the generated code and parse responses.

apollo-api-java contains the symbols needed to compile the Java models.

apollo-ast contains code to parse GraphQL documents and manipulate their Abstract Syntax Tree.

apollo-compiler is the low level compiler API used by apollo-gradle-plugin.

apollo-debug-server is a server that serves your normalized cache to the IntelliJ/Android Studio plugin.

apollo-engine-tests contains a list of tests for implementations of HttpEngine and WebSocketEngine.

apollo-execution contains code to execute GraphQL documents. apollo-execution requires coroutines and apollo-api.

apollo-gradle-plugin contains the Apollo Gradle plugin.

apollo-gradle-plugin-external does not contain any code. It is a Maven relocation that redirects to apollo-gradle-plugin

apollo-gradle-plugin-tasks contains the task implementations for the Apollo Gradle plugin.

apollo-http-cache is a HTTP cache for your GraphQL operations. Compared to a regular HTTP cache, it also caches POST requests.

apollo-mpp-utils contains a few utilities for working with multiplatform projects.

apollo-normalized-cache contains ApolloStore and ApolloCacheInterceptor. It bridges ApolloClient and ApolloNormalizedCache.

apollo-normalized-cache-api is the low-level cache. It knows nothing about coroutines and/or apollo-runtime and contains a memory implementation of NormalizedCache.

apollo-normalized-cache-sqlite contains an implementation of NormalizedCache that uses SQLite to persist the data across app restarts.

apollo-runtime contains ApolloClient, networking code to execute your queries and subscriptions. This is the main entry point.

apollo-testing-support contains QueueTestNetworkTransport and MapTestNetworkTransport for testing without a mock server.

apollo-tooling contains APIs to work with GraphQL schemas and operations as well as the GraphOS API. It is used from the CLI and Gradle plugin