Installation - MCP PHP SDK
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Installation

The SDK ships as a single Composer package:

composer require mcp/sdk

It requires PHP 8.1+ and the fileinfo extension. Most of what it pulls in is PSR interface packages (psr/container, psr/log, psr/http-message, …); the rest is opis/json-schema for schema validation, symfony/uid for session identifiers, phpdocumentor/reflection-docblock for reading descriptions out of your docblocks, php-http/discovery for finding PSR-17/PSR-18 implementations, and symfony/deprecation-contracts for deprecation notices.

That is enough for a complete STDIO server and for the STDIO client.

Optional packages

Which extras you need depends on what you build:

You want to… Also install
discover #[McpTool] & friends from a directory symfony/finder
serve over HTTP any PSR-17 implementation, e.g. nyholm/psr7
emit the response from a standalone HTTP entry point laminas/laminas-httphandlerrunner
connect a client over HTTP any PSR-18 client, e.g. symfony/http-client
validate JWT access tokens firebase/php-jwt
store sessions, cache discovery or share notifications through a PSR-16 cache psr/simple-cache implementation, e.g. symfony/cache
fetch JWT keys from an issuer with JwtTokenValidator::fromIssuer() psr/cache (PSR-6) implementation, e.g. symfony/cache

PSR-17 and PSR-18 implementations are found through php-http/discovery, so installing the package is all that is needed — no wiring:

composer require nyholm/psr7

If discovery picks the wrong one, or you want to be explicit, pass the factories to the transport yourself; see HTTP transport.

Next

Write your first server.