AxonOps Schema Registry

AxonOps Schema Registry is a self-hosted registry for schemas used with Apache Kafka. It best suits teams that want to control their registry infrastructure and storage, particularly those already using Confluent-compatible clients. Its breadth is appealing, but it is not a managed service: teams must run and maintain it themselves.

Overview

The registry offers an API-compatible alternative to Confluent Schema Registry, with support for Avro, Protobuf, and JSON Schema, including schema references. It can store schemas in PostgreSQL, MySQL, or Cassandra without using Kafka as its storage backend. That gives teams flexibility to fit the registry into an existing database setup; Cassandra users must be on version 5.0 or later.

The software is a statically linked binary of about 50 MB, deployable as a Docker container or buildable from source. That compact packaging suits teams comfortable operating their own services, but the self-hosted model puts deployment and ongoing operations on them. AxonOps offers commercial support plans, while the project also welcomes community issues and contributions.

Key features

The maker says existing Confluent serializers and Java, Go, and Python Kafka clients can use the registry by pointing them at its URL. For teams with those clients in place, this offers a route to adoption without changing their serializer choice. Compatibility settings range across NONE, backward and forward modes, their transitive variants, and FULL, giving teams options for how schema changes are checked.

Security is a substantial part of the package: Basic Auth, API keys, JWT, LDAP/AD, OIDC, mTLS, four RBAC roles, rate limiting, and automatic TLS certificate reload are built in. Audit events can go to stdout, rotating files, syslog over TCP/TLS, or webhooks, in JSON or CEF. This range is useful for teams that need multiple authentication, authorization, and audit paths; it also means operators must choose and configure the mechanisms that fit their environment.

Client-side field encryption includes a DEK/KEK registry and production-ready integrations with HashiCorp Vault and OpenBao Transit. Data contracts add metadata tags and domain, migration, and encoding rules to schemas, with defaults and per-subject overrides. These features give teams controls beyond basic schema registration, though their value depends on whether those governance and encryption needs are part of the job.

A built-in MCP server connects with AI clients including Claude, Cursor, VS Code Copilot, and Windsurf, but it is marked beta. Teams evaluating it should treat that integration as experimental rather than a settled reason to choose the registry.

Pricing

AxonOps Schema Registry is free and open source under the Apache 2.0 license. The AxonOps Schema Registry plan costs nothing, is billed 100% free, and has no hidden costs, premium tiers, or license keys. There are no paid feature tiers to weigh against the free plan. The trade-off is operational rather than financial: self-hosters provide the infrastructure and day-to-day administration, and commercial support is offered separately by AxonOps.

Platforms

AxonOps Schema Registry is available for API use on Linux and as self-hosted software. Docker deployment and source builds give teams two ways to run it, while the single-binary packaging keeps the deployment footprint compact. It is not presented as a hosted registry service.

Who it's for

This is a strong fit for Kafka teams that want an open-source, self-managed registry, need support for several schema formats, or prefer PostgreSQL, MySQL, or Cassandra for schema storage. It is also worth considering when built-in authentication, audit routing, field encryption, or data-contract rules matter. Teams seeking a managed registry, those unwilling to own operations, and Cassandra users running versions before 5.0 should look elsewhere.

Pros and cons

• Pros: Avro, Protobuf, and JSON Schema support, schema references, and seven compatibility modes cover a broad range of schema workflows.
• Pros: PostgreSQL, MySQL, or Cassandra storage avoids making Kafka the registry backend.
• Pros: Extensive built-in security, audit, encryption, and contract options suit teams with specific governance requirements.
• Pros: The Apache 2.0 license and free plan have no license keys or premium tiers.
• Cons: Self-hosting means the team owns deployment and operations rather than relying on a managed service.
• Cons: Cassandra storage requires version 5.0 or later, excluding earlier installations.
• Cons: The MCP server is beta, so AI integration should not be treated as a mature capability.

Alternatives

Choose Lenses if you want to compare a freemium Kafka option that also has a free trial and a community replication plan capped at five topic partitions per replica, without exactly-once delivery. Apache Pulsar is another free, open-source option to consider if you are comparing broader messaging software rather than choosing only a Kafka schema registry.

Confluent Cloud is the alternative to consider if a fully managed Kafka service and autoscaling resources matter more than self-hosting; its free Basic plan also includes more than 80 managed connectors. TIBCO Messaging Schema Repository for Apache Kafka offers a community edition for up to 100 production application instances or 1,000 web/mobile instances, with no TIBCO support in that edition.

AWS Glue Schema Registry may suit readers seeking a free registry with regional account quotas, including up to 100 registries and 10,000 schema versions per Region per account. Buf Schema Registry is worth comparing if a hosted repository model appeals: its free Community plan includes one private repository, unlimited public repositories, and Community Slack support.

Google Cloud Pub/Sub is a broader messaging alternative with a free usage allowance of 10 GiB throughput, followed by a listed $40 a month pay-as-you-go plan after that allowance. Karapace is a closer self-hosted registry alternative if its free plan's stated limits—250 KiB/s throughput, retention up to three days, and up to five topics with two partitions each—fit your workload.

For a wider comparison, browse Schema Registry Software.

Verdict

Choose AxonOps Schema Registry if your Kafka team wants a free, self-hosted registry with broad format support, flexible database storage, and substantial security and governance controls. The decisive reason to look elsewhere is operational: teams wanting a managed service should choose a hosted alternative, while Cassandra users must first meet the 5.0 minimum.