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# URI Contract

This page defines the canonical resource URI contract, template parameter rules, and compatibility policy.

Conventions in this document follow [MCP resource semantics](https://modelcontextprotocol.io/docs/learn/server-concepts#resources), [URI generic syntax (RFC3986)](https://www.rfc-editor.org/rfc/rfc3986), and [URI templates (RFC6570)](https://www.rfc-editor.org/rfc/rfc6570).

## Canonical URI Surface

The public, preferred direct resource URIs are:

1. `resource://catalog/skills_index`
2. `resource://catalog/skills/{skill_id}`
3. `resource://skills/{skill_id}/document`
4. `resource://skills/{skill_id}/references/{ref_id}`
5. `resource://docs/{path*}`
6. `resource://catalog/prompts_index`
7. `resource://catalog/prompts/{prompt_id}`
8. `resource://prompts/{prompt_id}/document`

The public, preferred resource template URIs are:

1. `resource://catalog/skills_index{?q,tag,capability,cursor,limit}`
2. `resource://catalog/prompts_index{?q,tag,cursor,limit}`

Contract intent:

1. Catalog URIs are discovery surfaces.
2. Skill URIs are the primary per-skill guidance surfaces.
3. Catalog query templates are additive discovery helpers for filtering and pagination.
4. The docs wildcard URI is a direct authored-markdown access surface under `docs/`.

Best-practice alignment:

1. Resource identifiers are stable and noun-oriented.
2. Dynamic lookup variants are represented as RFC6570 templates.
3. Resources remain read-oriented and are described with explicit MIME types.

## URI Semantics

### `resource://catalog/skills_index`

1. Returns a compact list of skill records for discovery.
2. Contains one entry per `skill_id`.
3. Includes enough metadata for client-side selection, at minimum `id`, `name`, `description`, `tags`, and `capabilities`.

### `resource://catalog/skills/{skill_id}`

1. Returns one normalized record for `skill_id`.
2. Includes the canonical document URI and declared reference ids.
3. Returns not found when `skill_id` does not exist.

### `resource://skills/{skill_id}/document`

1. Returns the canonical `SKILL.md` authored content for that skill.
2. `skill_id` must satisfy the stable skill id rules from the content contract.

### `resource://skills/{skill_id}/references/{ref_id}`

1. Returns one reference document declared in the skill frontmatter references manifest.
2. `ref_id` is the stable public handle for that reference document.

### `resource://docs/{path*}`

1. Returns authored markdown at a normalized relative path under `docs/`.
2. Supports nested paths via [RFC6570 wildcard expansion](https://www.rfc-editor.org/rfc/rfc6570).
3. Typical examples include `index.md`, `usage.md`, `skills/<skill-id>/SKILL.md`, and `skills/<skill-id>/references/<file>.md`.

### `resource://catalog/prompts_index`

1. Returns a compact list of prompt records for discovery.
2. Contains one entry per `prompt_id`.
3. Includes `id`, `name`, `description`, `tags`, `version`, and canonical document URI.

### `resource://catalog/skills_index{?q,tag,capability,cursor,limit}`

1. Returns the same record family as `resource://catalog/skills_index` with optional filtering and pagination.
2. Query parameters are optional and composable.
3. Unknown query keys are ignored or rejected deterministically by server policy.

### `resource://catalog/prompts_index{?q,tag,cursor,limit}`

1. Returns the same record family as `resource://catalog/prompts_index` with optional filtering and pagination.
2. Query parameters are optional and composable.
3. Unknown query keys are ignored or rejected deterministically by server policy.

### `resource://catalog/prompts/{prompt_id}`

1. Returns one normalized record for `prompt_id`.
2. Includes prompt argument metadata when declared in frontmatter.
3. Returns not found when `prompt_id` does not exist.

### `resource://prompts/{prompt_id}/document`

1. Returns the canonical prompt markdown document.
2. `prompt_id` must satisfy lowercase kebab-case rules.

## Template Parameter And Validation Rules

### `skill_id`

1. Lowercase kebab-case.
2. Must satisfy the stable skill id rules from the content contract.

### `ref_id`

1. Lowercase kebab-case.
2. Must be declared in the skill's references manifest.

### `path*`

1. Relative POSIX path only, expressed as URI path segments under [RFC3986 path syntax](https://www.rfc-editor.org/rfc/rfc3986#section-3.3).
2. No leading slash.
3. No `..` traversal segments.
4. Resolves only inside `docs/`.
5. Markdown-only in the end state, meaning `.md` files.
6. Any reserved URI characters in path segments must be [percent-encoded](https://www.rfc-editor.org/rfc/rfc3986#section-2.1).

### `prompt_id`

1. Lowercase kebab-case.
2. Must be unique across prompt ids and must not collide with skill ids.

## URI Hygiene Rules

1. Use lowercase, human-readable path segments for stable discoverability.
2. Keep identifiers immutable once public whenever practical.
3. Keep template variables semantic (`skill_id`, `prompt_id`, `ref_id`, `path*`) and avoid overloading one variable for unrelated meanings.
4. Do not include secrets, tokens, or user-identifying data in URI paths or query strings.
5. Prefer additive query parameters for discovery over introducing parallel URI families, matching [MCP resource-template discovery patterns](https://modelcontextprotocol.io/docs/learn/server-concepts#resources).
6. Return clear not-found semantics for unknown ids and invalid template resolution.

## URI Versioning Policy

Default rule:

1. Keep URIs unversioned by default.
2. Allow URI and payload updates when they improve clarity or implementation simplicity.

Breaking-change rule:

1. Breaking changes use direct replacement of the canonical URI family.
2. No compatibility aliases or dual URI families are maintained.

FastMCP version metadata usage:

1. Resource `version` metadata may be used for implementation and version discovery.
2. URI readability and maintainability remain the primary contract.

## Reference Id Compatibility Policy

`ref_id` is the public identifier for a reference document, separate from file path.

Rules:

1. Prefer keeping `ref_id` stable when practical.
2. File paths may change without URI churn as long as the mapped `ref_id` still resolves.
3. If a reference is renamed, introduce a new `ref_id` and treat the old one as retired.
4. Avoid reusing retired `ref_id` values for unrelated content.

## Invariants

This contract guarantees:

1. One canonical URI pattern per core capability surface.
2. Fast, low-friction URI evolution through direct replacement of canonical URIs.
3. A single canonical catalog URI family with no alias maintenance overhead.
4. Reference mappings can evolve with minimal churn.

## Non-Goals

This contract does not define:

1. Implementation-specific transform wiring details, such as `VersionFilter`, mounts, or provider composition.
2. Migration script mechanics for auto-generating aliases.
3. Authorization policy design for URI-level access control.

## Sources

1. [MCP Server Concepts: Resources](https://modelcontextprotocol.io/docs/learn/server-concepts#resources)
2. [MCP Architecture Overview](https://modelcontextprotocol.io/docs/learn/architecture)
3. [MCP Specification Repository](https://github.com/modelcontextprotocol/spec)
4. [RFC6570 URI Template](https://www.rfc-editor.org/rfc/rfc6570)