MCP Server Capabilities: What a Server Declares in initialize

Capabilities are the feature sets a client and server declare during initialize. Each side announces what it supports, such as tools, resources, prompts, or logging, and neither is expected to use anything the other did not declare. It is a negotiation, not a fixed list every implementation has to satisfy.

What are MCP capabilities?

Capabilities are the declared feature sets exchanged during initialize. The server says what it offers; the client says what it can consume. Each side reads the other's declaration and adjusts.

This is how the protocol supports partial implementations without every client needing to handle every feature.

What does a server's capabilities object look like?

It sits in the server's answer to initialize, next to protocolVersion and serverInfo. A server offering every common feature sends something like this [1]:

"capabilities": {
  "tools": { "listChanged": true },
  "resources": { "subscribe": true, "listChanged": true },
  "prompts": { "listChanged": true },
  "logging": {},
  "completions": {}
}

tools: the server has tools a client can list and call. listChanged means it will send a notification when the list changes.
resources: the server exposes readable data such as files or records. subscribe lets a client ask to be told when one resource changes; listChanged covers the list itself.
prompts: the server offers prompt templates, with the same listChanged flag.
logging: the server will send log messages, and a client can set the level it wants.
completions: the server can suggest values for prompt and resource arguments as a user types.

A key that is missing means the feature is not offered. An empty object, as with logging here, means it is offered with no options. There is also experimental, for non-standard features a server and client agree on between themselves.

On the 2026-07-28 revision there is no initialize: the same object comes back from server/discover (stateless MCP). Almost every server we have called still answers initialize.

What can a server declare?

The common ones are tools, resources, and prompts. A server can also declare support for subscriptions and for change notifications, signalling that it will tell the client when its lists change instead of expecting a poll.

Tools are the capability nearly everyone implements and the one worth checking first: a server declaring tools is a server you can call tools/list against.

Why does the declaration matter if you can just try the call?

Because a well-behaved client should not call what was never offered, and a server is entitled to reject a method it did not declare. Trying anyway turns a clean negotiation into error handling.

It also matters for reading a connection record honestly. A server that declares only resources and no tools is working correctly when tools/list returns nothing, and describing that as a failure would be wrong.

Example

Every one of the 14 servers we reached on 5 August 2026 declared tool support and answered tools/list, returning 288 tools between them. A server declaring only prompts would have completed the same initialize exchange perfectly well and then had nothing to say to a tool-oriented client, which is a difference in capability rather than a difference in quality.

Sources

Lifecycle, MCP specification 2025-11-25

capabilities