JSON-RPC Methods

What the handler answers, and on which era.

Every method below is implemented for you. You never register a method — you declare tools, resources, and prompts, and the methods that expose them exist.

#Shared

Method	Answers with
`tools/list`	Declared tools, paginated, schemas resolved
`tools/call`	Tool result, after validating `arguments`
`resources/list`	Declared resources, paginated
`resources/read`	Resource contents; falls back to URI templates
`resources/templates/list`	Declared resource templates, paginated
`prompts/list`	Declared prompts, paginated
`prompts/get`	Prompt messages, after checking required args
`completion/complete`	Values from a `complete` callback

#Modern Only

Method	Answers with
`server/discover`	Versions, capabilities, instructions, identity (cacheable)
`subscriptions/listen`	A long-lived SSE stream of opted-in notifications

#Legacy Only

Method	Answers with
`initialize`	Negotiated version, capabilities, `serverInfo`
`notifications/initialized`	Accepted, no-op
`ping`	Empty result
`notifications/cancelled`	Aborts the named in-flight request (alias: `notifications/canceled`)
`notifications/progress`	Invokes `onProgress`
`resources/subscribe`	Invokes `onSubscribe`
`resources/unsubscribe`	Invokes `onUnsubscribe`
`logging/setLevel`	Invokes `onLogLevelSet`

An unknown method is -32601, with HTTP 404 on the modern era.

#Pagination

tools/list, resources/list, resources/templates/list, and prompts/list are cursor-paginated. Clients pass the nextCursor from the previous page; the cursor is opaque and validated, so a malformed one is -32602 rather than an unbounded read.

curl -X POST http://localhost:3000/mcp \
  -H 'content-type: application/json' \
  -d '{ "jsonrpc": "2.0", "id": 1, "method": "tools/list",
        "params": { "cursor": "eyJvZmZzZXQiOjEwfQ==" } }'

#Capabilities

Capabilities are derived, never declared by hand:

Capability	Advertised when
`tools`	at least one tool
`resources`	at least one resource or resource template
`prompts`	at least one prompt
`completions`	any prompt argument or template has a `complete` callback
`logging`	`onLogLevelSet` (legacy) or `logging: true` (modern)
`resources.subscribe`	`onSubscribe` (legacy) or `onListen` (modern)
`*.listChanged`	always (legacy) · `onListen` (modern)
`extensions`	`extensions` is set (modern)