# Reference

Formats and behavior for publishers, registry operators, and client builders. If you are new to Open Service Directory (OSD), start with [Discover support](/0.3.0/docs/guides/discover-support/) or [Publish a support agent](/0.3.0/docs/guides/publish-a-support-agent/).

## Data and compatibility

- [OSD entry requirements](/0.3.0/docs/reference/osd-profile/): required fields, publication, and endorsement.

## Discovery components

- [Registry](/0.3.0/docs/reference/registry/): search requests, complete result entries, and admission.
- [Registry directory](/0.3.0/docs/reference/osd-directories/): participating registries, search endpoints, and the directory format.
- [Client](/0.3.0/docs/reference/client/): what discovery code in an application is responsible for.
- [CLI (coming soon)](/0.3.0/docs/reference/cli/): a preview of the open-source CLI's search, verification, and direct MCP commands.