# Roots (client feature, 2025-11-25)

## Metadata

| Field | Value |
|---|---|
| Institute | Molodetz Institute - Research & Retrieval Division |
| Subject | mcp-client-support |
| Document type | Source Dossier |
| Tier | 1 |
| Source title | Roots (MCP Specification v2025-11-25) |
| Source URL | https://modelcontextprotocol.io/specification/2025-11-25/client/roots |
| Source publisher / author | Model Context Protocol authors (Anthropic-donated open project; site docs) |
| Source type | standard |
| Source date (published) | 2025-11-25 (version stamp; no other publish date stated) |
| Date researched | 2026-10-18 |
| Researched by | tai (agent), model: Claude Sonnet 5, on behalf of retoor |
| Research method | gather-subagent direct page fetch, parent synthesis from evidence pack |
| Confidence | High (partial read; findings cover retrieved sections only, see Cons) |
| Status | Active |

## Summary

Roots is a server-initiated client feature: supporting clients declare the `roots` capability, answer server `roots/list` requests with `file://` URIs, and emit `notifications/roots/list_changed` when their roots change (if `listChanged` was declared). Clients without the feature return `-32601` (Method not found). It is cleanly optional: a minimal client omits the capability and answers with the standard error.

## Key findings

- "Clients that support roots MUST declare the `roots` capability during initialization" (`{"roots":{"listChanged":true}}`).
- Server-to-client request `roots/list`; response `{"roots":[{"uri":"file:///…","name":…}]}`; a root `uri` "MUST be a `file://` URI in the current specification."
- Clients with `listChanged` "MUST send" `notifications/roots/list_changed` on change.
- Unsupported: return `-32601` (Method not found), e.g. `"message": "Roots not supported"`.

## Pros / strengths

- Minimal surface for a server-initiated feature: one request, one optional notification, one capability flag.
- The unsupported path is specified with a literal error code and message, so omission is compliant behavior rather than a gap.
- `file://`-only URIs in the current spec keep validation trivial for any client that does implement it.

## Cons / limitations / caveats

- Per the pack's Uncertainty notes this page was only partially read; findings cover the retrieved sections, and deeper subsections were not read.
- No explicit author names or publish dates appear on the page; the date above is the version stamp in the URL.
- Deprecated in the 2026-07-28 revision ("Deprecate the Roots, Sampling, and Logging features… new implementations should not add support"), and server-initiated requests are replaced by MRTR there, so new roots code is handshake-era-only investment.

## Relevance to tai

Optional server-initiated feature; a minimal client simply omits the capability and answers `roots/list` with `-32601`. Relevant to tai mainly as the pattern for all three skippable client features: omit capability, return Method not found if asked.

## Changelog

| Date | Change |
|---|---|
| 2026-10-18 | Initial dossier created. |