> ## Documentation Index
> Fetch the complete documentation index at: https://retrievalcontextprotocol.com/llms.txt
> Use this file to discover all available pages before exploring further.

# The method set

> Every RCP method, the capability that gates it, and its purpose.

Every method after `initialize` is **gated** by a capability the server
advertised. Clients check `supports(...)` before calling — failures surface
*client-side* as `CapabilityMissing` (`-32003`) before any I/O.

| Method                                                                        | Capability    | Purpose                                                        |
| ----------------------------------------------------------------------------- | ------------- | -------------------------------------------------------------- |
| [`initialize`](/concepts/initialization) / [`info`](/concepts/initialization) | always        | Version + capability handshake / stateless identity.           |
| [`embed`](/methods/embed)                                                     | `embed`       | Dense embeddings.                                              |
| [`embed/sparse`](/methods/embed)                                              | `sparseEmbed` | Learned-sparse terms (SPLADE).                                 |
| [`embed/multi`](/methods/embed)                                               | `multiVector` | Per-token / per-patch vectors (ColBERT, ColPali).              |
| [`rerank`](/methods/rerank)                                                   | `rerank`      | Cross-encoder / late-interaction scoring.                      |
| [`retrieve`](/methods/retrieve)                                               | `retrieve`    | The workhorse — mode, filter, rerank, MMR, recency, citations. |
| [`query/transform`](/methods/query-transform)                                 | `transform`   | Expansion / HyDE / decomposition.                              |
| [`graph`](/methods/graph)                                                     | `graph`       | GraphRAG local / global / drift.                               |
| [`memory/build`, `memory/recall`](/methods/memory)                            | `memory`      | Global/session memory → clues (MemoRAG, HippoRAG).             |
| [`feedback`](/methods/feedback)                                               | `feedback`    | Client→server relevance / reward / integrity signals.          |
| [`index/add`, `index/delete`](/methods/index)                                 | `index`       | Mutate the corpus.                                             |
| [`catalog/list`](/methods/catalog)                                            | `catalog`     | Enumerate federated engines.                                   |
| [`notifications/cancel`](/concepts/lifecycle)                                 | always        | Abandon an in-flight request.                                  |
| [`notifications/log`](/features/observability)                                | `log`         | Server-emitted structured diagnostics.                         |
| [`ping`](/concepts/lifecycle)                                                 | always        | Liveness / round-trip; echoes a nonce.                         |
| [`shutdown`](/concepts/lifecycle)                                             | always        | Graceful close.                                                |

<Note>
  `retrieve` is the workhorse: a single call can drive query transform, hybrid
  recall, rerank, MMR diversification, recency weighting, metadata filtering, and
  citation assembly — whatever the engine advertises.
</Note>

## Naming conventions

* Method names are `<verb>` or `<verb>/<sub>` — `retrieve`, `index/add`.
* The `notifications/` prefix is reserved for protocol notifications (no `id`).
* The `x-<vendor>/<name>` space is for [vendor extensions](/concepts/extensibility).

## Always-available methods

Four methods need **no capability** and (except where noted) work at any time:

<CardGroup cols={2}>
  <Card title="initialize / info" icon="play" href="/concepts/initialization">
    Handshake and stateless identity. `info` and `ping` answer even before
    `initialize`.
  </Card>

  <Card title="ping" icon="wifi" href="/concepts/lifecycle">
    Liveness and round-trip timing; echoes a nonce.
  </Card>

  <Card title="shutdown" icon="power-off" href="/concepts/lifecycle">
    Graceful close; EOF on stdin is equivalent.
  </Card>

  <Card title="notifications/cancel" icon="ban" href="/concepts/lifecycle">
    Abandon an in-flight request; best-effort, no response.
  </Card>
</CardGroup>