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

# Discovery

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`server/discover` lets a client query a server's supported protocol versions,
capabilities, and identity before sending any other requests. Servers **MUST**
implement it.

## Request

The request carries no body parameters beyond the standard `_meta`:

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": "discover-1",
  "method": "server/discover",
  "params": {
    "_meta": {
      "io.modelcontextprotocol/protocolVersion": "2026-07-28",
      "io.modelcontextprotocol/clientInfo": {
        "name": "ExampleClient",
        "version": "1.0.0"
      },
      "io.modelcontextprotocol/clientCapabilities": {}
    }
  }
}
```

## Response

The server replies with its supported protocol versions, capabilities, and
identity. This operation supports [caching](/specification/draft/server/utilities/caching).

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": "discover-1",
  "result": {
    "resultType": "complete",
    "supportedVersions": ["2026-07-28"],
    "capabilities": {
      "tools": {},
      "resources": {}
    },
    "serverInfo": {
      "name": "ExampleServer",
      "version": "1.0.0"
    },
    "instructions": "This server provides weather and resource utilities.",
    "ttlMs": 3600000,
    "cacheScope": "public"
  }
}
```

### Response Fields

| Field               | Type                 | Required | Description                                                                                  |
| ------------------- | -------------------- | -------- | -------------------------------------------------------------------------------------------- |
| `supportedVersions` | `string[]`           | yes      | Protocol versions the server supports. The client should choose one for subsequent requests. |
| `capabilities`      | `ServerCapabilities` | yes      | Capabilities the server supports (tools, resources, prompts, etc.).                          |
| `serverInfo`        | `Implementation`     | yes      | Name and version of the server software.                                                     |
| `instructions`      | `string`             | no       | Natural-language guidance for LLMs on how to use this server effectively.                    |

## When to Call

Calling `server/discover` is optional for clients — a client may invoke any
RPC inline and handle
[`UnsupportedProtocolVersionError`](/specification/draft/schema#unsupportedprotocolversionerror)
if the server does not support the requested version. However, `server/discover`
is useful in two scenarios:

* **Up-front version selection.** The client learns the server's supported
  versions before sending any other request, avoiding a round-trip error.
* **stdio backward-compatibility probe.** On stdio, there is no per-request
  HTTP status code to drive fallback. A client that supports both modern
  (per-request `_meta`) and legacy (`initialize` handshake) servers **SHOULD**
  send `server/discover` first; see
  [stdio: Backward Compatibility](/specification/draft/basic/transports/stdio#backward-compatibility)
  for the fallback rules.

See [Protocol Version Negotiation](/specification/draft/basic/versioning#protocol-version-negotiation)
for the full version-selection flow. For HTTP-specific status codes returned for
unknown methods, see the [Protocol Version Header](/specification/draft/basic/transports/streamable-http#protocol-version-header)
section in Transports.
