GraphQL Kotlin vs WunderGraph Cosmo

GraphQL Kotlin is a free Apache License 2.0 collection of libraries, built on graphql-java, for running GraphQL clients and servers in Kotlin. Its schema generator creates schemas from Kotlin code, and a federation module can produce Apollo Federation-compliant schemas. Gradle and Maven plugins generate type-safe Kotlin clients from existing schemas. Generated clients support queries, mutations, batching, coroutines, custom scalars, configurable enum defaults, and Jackson or kotlinx.serialization models. Reference HTTP integrations use Ktor HTTP Client and Spring WebClient, while custom engines are possible. Server implementations target Spring Boot and Ktor; the Spring server uses Spring WebFlux. Ktor supports Kotlin Flow subscriptions over WebSockets with the graphql-transport-ws subprotocol. Its plugin leaves route configuration to the application, allowing selective routes and added authentication logic. The schema generator supports Kotlin Lists, but Sets, arbitrary Maps, and arrays are not supported out of the box. The project is self-hosted, with security guidance in its repository and community support through GitHub Discussions and Kotlin Slack.

WunderGraph Cosmo is an open-source GraphQL Federation platform for platform teams, offering schema checks, guardrails and observability. It unifies GraphQL, REST, gRPC and Kafka in a federated graph and supports Apollo Federation versions 1 and 2 across existing GraphQL services. Cosmo Router is a Go-based, Apache 2.0-licensed router and gateway. Teams can deploy it with Docker, Kubernetes or an AWS Lambda-optimized binary, or use WunderGraph’s managed service. The Schema Registry checks composition, breaking changes, client traffic and linting. Subscriptions work over WebSockets and Server-Sent Events, and event-driven subscriptions can use Kafka, NATS, SQS or RabbitMQ. Cosmo Streams supports Kafka, NATS including JetStream, and Redis. Observability includes OpenTelemetry tracing and Prometheus metrics, which can be exported to compatible backends. The free Developer plan includes one federated graph, 10M requests/month, 10 subgraphs, one team member and seven-day retention. Launch costs $499 a month; Scale costs $3,499 a month. Enterprise pricing is custom. Managed plans include SOC 2 and HIPAA compliance; the site also identifies ISO 27001 certification.