AxonOps Schema Registry vs Buf Schema Registry

AxonOps Schema Registry is a free, Apache 2.0-licensed service for managing Apache Kafka schemas as an API-compatible replacement for Confluent Schema Registry. It handles Avro, Protobuf, and JSON Schema, including references and seven compatibility modes. Schemas can be stored in PostgreSQL, MySQL, or Cassandra, without requiring Kafka as the storage backend. The project says existing Confluent serializers and Java, Go, and Python Kafka clients can connect by changing the registry URL. Security options include Basic Auth, API keys, JWT, LDAP/AD, OIDC, mTLS, four RBAC roles, rate limiting, and TLS certificate auto-reload. Audit events can go to stdout, files, syslog, or webhooks. Client-side field encryption supports DEK/KEK registries and HashiCorp Vault or OpenBao Transit. Data contracts add metadata and rules. A beta MCP server supports several AI clients. It runs self-hosted on Linux, as a Docker container, or from source.

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.