7e507f2963
## Motivation and Context
The client answers server pings automatically, but the docs leave out where that applies and what the stdio transport
does with the other server-to-client requests.
The client Transports page now lists the automatic ping answer among the things the stdio transport handles,
and a note states that `ping` is the only server-to-client request answered there: a wire-level `elicitation/create`
or `sampling/createMessage` is ignored over stdio, so a server that sends one waits for an answer that never comes,
while the SEP-2322 `input_required` route works on every transport and keeps `on_elicitation` and `on_sampling` handlers
working over stdio. Without this note, the only trace of the limitation is a hung tool call.
The client Ping page now says that over HTTP a ping reaches the client only on a stream that is already open
and that the client never opens one to receive pings, so a server can only ping a client that has a stream open.
Registering `on_server_request("ping")` moves to the end of the section as the advanced option it is, together with
its side effect of opening the GET listening stream on `connect`.
The client overview mentions the automatic answer next to `MCP::Client#ping`,
and the server Ping page's Client Side section points at it.
## How Has This Been Tested?
Documentation only; the linked headings and pages exist.
## Breaking Changes
None.
47 lines
2.4 KiB
Markdown
47 lines
2.4 KiB
Markdown
---
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layout: default
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title: Overview
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nav_order: 1
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permalink: /client/
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redirect_from:
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- /building-clients.html
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- /building-clients/
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---
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# Building an MCP Client
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The `MCP::Client` class provides an interface for interacting with MCP servers.
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This class supports:
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- Lifecycle negotiation and connection via `MCP::Client#connect`, adopting the modern lifecycle
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when the server serves it; see [Lifecycle](/client/lifecycle/)
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- Server discovery via the `server/discover` method (`MCP::Client#discover`); see [Explicit Discovery](/client/lifecycle/#explicit-discovery)
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- Liveness check via the `ping` method (`MCP::Client#ping`), and automatic answers to server pings;
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see [Answering Server Pings](/client/ping/#answering-server-pings)
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- Tool listing via the `tools/list` method (`MCP::Client#tools`)
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- Tool invocation via the `tools/call` method (`MCP::Client#call_tool`)
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- Resource listing via the `resources/list` method (`MCP::Client#resources`)
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- Resource template listing via the `resources/templates/list` method (`MCP::Client#resource_templates`)
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- Resource reading via the `resources/read` method (`MCP::Client#read_resource`)
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- Prompt listing via the `prompts/list` method (`MCP::Client#prompts`)
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- Prompt retrieval via the `prompts/get` method (`MCP::Client#get_prompt`)
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- Completion requests via the `completion/complete` method (`MCP::Client#complete`); see [Completion](/server/completion/)
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- Automatic driving of multi round-trip `input_required` results once `on_elicitation`, `on_sampling`,
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or `on_roots` handlers are registered; see [Multi Round-Trip Requests](/client/mrtr/)
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- Cancellation of in-flight requests via the `cancellation:` keyword; see [Cancellation](/client/cancellation/)
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- Cursor-based page iteration on the `list_*` methods and whole-collection fetching with
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the `max_pages` guard; see [Pagination](/client/pagination/)
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- Automatic JSON-RPC 2.0 message formatting
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- UUID request ID generation
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Clients are initialized with a [transport layer](/client/transports/) instance that handles the low-level communication mechanics.
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Authorization is handled by the transport layer; see [Authorization](/client/authorization/).
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## Tool Objects
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The client provides a wrapper class for tools returned by the server:
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- `MCP::Client::Tool` - Represents a single tool with its metadata
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This class provides easy access to tool properties like name, description, input schema, and output schema.
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