# opam

Recommend AXM extensions from an opam (OCaml) package and target opam packages from an extension.

AXM reads OCaml extension metadata from the `x-agent-extensions` custom field in
the package's `.opam` file. This is the
[two-way linking](/docs/package-ecosystems/overview) model applied to the opam
ecosystem. opam reserves the `x-` prefix for extension fields, and AXM decodes
each one against the package metadata schema.

## Recommend extensions from a package

Add an `x-agent-extensions` field to the `.opam` file. Its value is a JSON array
of extension declarations, where each entry is an extension reference
(`@owner/<type>/<name>`):

```
# agentxm-example-tinyflags.opam
x-agent-extensions: [{"ref":"@examples/packs/ocaml-opam-tinyflags"}]
```

The field contains the portable recommendation entries directly.

Keep recommendations **identity-only** — omit `versionRange`. AXM resolves the
reference to the newest matching extension version and pins it in the user's
`axm.lock`. Prefer recommending a single **pack** so you keep one stable
reference while its contents evolve.

Add a semver `versionRange` only when your package genuinely pairs with a
bounded major line of the extension:

```
x-agent-extensions: [{"ref":"@examples/packs/ocaml-opam-tinyflags","versionRange":"^1.0.0"}]
```

## Target opam packages from an extension

On the extension manifest (`skill.json`, `pack.json`, `subagent.json`, …), add a
`packages` array with an opam [purl](https://github.com/package-url/purl-spec).
Use the package name as published to the opam repository as the purl name:

```jsonc
// pack.json
{
  "packages": [{ "purl": "pkg:opam/agentxm-example-tinyflags" }],
}
```

### Version ranges

Default to identity-only. Add a [VERS](https://github.com/package-url/vers-spec)
`versionRange` with the `opam` scheme only when the extension depends on package
APIs introduced or removed in a known range:

```jsonc
{
  "packages": [
    {
      "purl": "pkg:opam/agentxm-example-tinyflags",
      "versionRange": "vers:opam/>=0.1.0|<1.0.0",
    },
  ],
}
```

## Official status

When the opam package recommends an extension through the AgentXM Registry
**and** that extension names the package as a companion via its purl, AXM
derives **official** status for the pair — no extra flag. See
[Official extensions](/docs/package-ecosystems/overview#official-extensions).

## Reference fixture

The
[`ocaml-opam-lib`](https://github.com/agentxm/polyglot-examples/tree/main/ocaml-opam-lib)
and
[`ocaml-opam-app`](https://github.com/agentxm/polyglot-examples/tree/main/ocaml-opam-app)
directories in `polyglot-examples` are the working fixtures for everything
above. The package publishes a TinyFlags companion pack and recommends it from
the `x-agent-extensions` field in its `.opam` file; the pack and each skill
declare the package's `pkg:opam` purl as an identity-only companion package.