Buf Schema Registry vs Karapace

Buf Schema Registry (BSR) is a Protobuf-aware registry for managing API schemas, dependencies, and client access as APIs change. Teams publish Protobuf files as versioned modules and resolve dependencies declared in buf.yaml. BSR generates hosted SDKs for supported languages and browsable documentation from schema versions and comments. Server-side lint and breaking-change policies can reject updates or hold them for review. The registry also shows which modules depend on another, helping teams identify affected consumers before deprecation. A GitHub Action handles build, lint, formatting, breaking-change checks, and publishing; the Buf CLI can connect to other CI/CD systems. RPC APIs are available through Connect, gRPC, and gRPC-Web. Community costs nothing and includes one private repository limited to 100 types plus unlimited public repositories. Teams costs $0.50 a month per type and includes a 30-day trial. Pro costs $5 a month per type with a $3000/month minimum spend. Enterprise pricing is custom.

Karapace is Aiven’s open-source Schema Registry and REST Proxy for Aiven for Apache Kafka. The registry stores and versions schemas, then checks compatibility before a changed schema is published. It accepts Avro, Protobuf, and JSON Schema, with references supported for Avro and Protobuf. Compatibility modes include NONE, BACKWARD, BACKWARD_TRANSITIVE, FORWARD, FORWARD_TRANSITIVE, FULL, and FULL_TRANSITIVE. The REST Proxy exposes HTTP endpoints for producing and consuming Kafka events, so scripts, curl, and HTTP services can work with events. OAuth 2.0/OIDC authentication is available for both components. Registry ACLs and OIDC role-based rules can limit operations, including by HTTP method. Example identity providers include Auth0, Okta, Google Identity Platform, and Azure. Deployment documentation covers Docker and installation from source with pip; the API is stated to support Schema Registry 6.1.1 operations. Karapace is available in Aiven’s Kafka free tier for learning, prototyping, and evaluation. The Free plan costs nothing, while Developer costs $35 a month.