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# URI Contract

This page defines the public resource URI contract for native skills, registry-backed prompts, and general authored documentation.

## Native Skill URIs

The [FastMCP Skills Provider](https://gofastmcp.com/servers/providers/skills) publishes each skill through the `skill://` scheme:

1. `skill://<skill-name>/SKILL.md`
2. `skill://<skill-name>/_manifest`
3. `skill://<skill-name>/<supporting-path>`

The first two are concrete resources returned by `resources/list`. Supporting files use a per-skill wildcard resource template when the provider is configured with `supporting_files="template"`:

```text
skill://<skill-name>/{path*}
```

### Main File

`skill://<skill-name>/SKILL.md` returns the canonical authored skill document. The skill directory name supplies `<skill-name>`, and the resource description comes from `SKILL.md` frontmatter.

### Manifest

`skill://<skill-name>/_manifest` returns JSON containing the skill name and every file beneath its directory. Each file entry includes:

1. relative POSIX path
2. byte size
3. SHA256 hash

Clients read the manifest before requesting supporting files. FastMCP client utilities such as `list_skills()` and `get_skill_manifest()` understand this contract directly.

### Supporting Files

Supporting files retain their real skill-relative paths. For example:

```text
skill://pytesting/references/pytest-docs.md
```

FastMCP confines reads to the selected skill directory. Absolute paths, traversal outside the directory, missing files, directories, and symlinks that resolve outside the skill root are rejected.

## Prompt And Docs URIs

Prompts and general documentation retain the existing registry-backed resource surface:

1. `resource://catalog/prompts_index`
2. `resource://catalog/prompts_index{?q,tag,cursor,limit}`
3. `resource://catalog/prompts/{prompt_id}`
4. `resource://prompts/{prompt_id}/document`
5. `resource://docs/{path*}`

Prompt ids remain lowercase kebab-case. The docs wildcard accepts normalized relative POSIX Markdown paths beneath `docs/` and rejects absolute paths, traversal segments, backslashes, and non-Markdown targets.

## Discovery Order

For skills:

1. list resources or call FastMCP `list_skills()`
2. select a skill by name and description
3. read `skill://<skill-name>/SKILL.md`
4. read `_manifest` when supporting material may be needed
5. fetch only the supporting paths relevant to the task

For prompts, use the prompt catalog or MCP prompt-object APIs.

## Compatibility Policy

The native `skill://` family directly replaces the repository's former custom skill URI and catalog surfaces. No compatibility aliases or dual registrations are maintained. Prompt and general-doc URIs are unaffected.

Skill renames are breaking because the directory name is part of every native skill URI. Supporting-file renames change the corresponding manifest path and URI.

## Sources

1. [FastMCP Skills Provider](https://gofastmcp.com/servers/providers/skills)
2. [MCP resources](https://modelcontextprotocol.io/specification/latest/server/resources)
3. [RFC 3986 URI syntax](https://www.rfc-editor.org/rfc/rfc3986)
4. [RFC 6570 URI templates](https://www.rfc-editor.org/rfc/rfc6570)