xRegistry defines an abstract model for managing metadata about resources and a REST-based interface for creating, modifying, deleting and discovering those resources. A core specification sets the model and APIs, and domain specifications extend it for endpoints, message definitions and schemas. It began under the CloudEvents project, split into its own project in April 2023, and was accepted to CNCF at the Sandbox maturity level on 5 June 2025. The latest release is v1.0-rc4 (19 August 2026).
xRegistry
xRegistry gives registries one shape. Rather than every schema registry, endpoint catalog or message
catalog inventing its own API, xRegistry defines a common model of groups, resources and versions and a
REST interface to manage and discover them, so generic tooling can work against any registry that conforms.
The name is written with a lowercase x, even at the start of a sentence.
- Core plus domains - The core specification defines the model and APIs; domain specifications for an Endpoint Registry, a Message Definitions Registry and a Schema Registry extend it, with proposed new specifications kept as working drafts.
- Release candidates - v1.0-rc1 shipped 1 April 2025; v1.0-rc4, released 19 August 2026, is the latest.
- Machine-readable schemas - Each domain spec publishes its document format as JSON Schema, Avro and
OpenAPI in a
schemas/directory, and the core model has its own JSON Schema. - Tooling - The project maintains a reference server and CLI, a code and file generation CLI (
xrcg), a web viewer, and proxies that expose NPM, PyPI, Maven, NuGet, OCI and MCP package registries through the xRegistry API. - CloudEvents lineage - It was first developed under CloudEvents and still shares that project’s weekly meetings and the CNCF Serverless Working Group. Apache 2.0.
Where it sits. xRegistry is the metadata layer beside CloudEvents: CloudEvents standardizes the event envelope, xRegistry catalogs the endpoints that send them and the message and schema definitions they carry — schemas expressed in formats such as JSON Schema, Avro and Protocol Buffers. It overlaps in purpose with the discovery that AsyncAPI and OpenAPI documents provide, but describes the registry that holds such documents rather than any one API.
