[Client] Add client-side elicitation support

The SDK could send elicitation/create requests from a server tool via
ClientGateway::elicit(), but the client could not receive them: there was
no request handler, and ElicitRequest was not registered in MessageFactory,
so incoming elicitation/create messages failed to parse.

This adds the client half, mirroring the existing Sampling pattern:

- Register ElicitRequest in MessageFactory so elicitation/create parses.
- ElicitationRequestHandler wraps a user callback and returns an
  ElicitResult (accept/decline/cancel) or an Error.
- ElicitationCallbackInterface defines the callback contract.
- ElicitationException forwards a specific message to the server; any
  other throwable returns a generic error.

Includes unit tests, a runnable client example against the elicitation
demo server, and client docs/README updates.

Author: wachterjohannes

README.md

@@ -210,6 +210,7 @@ $client->disconnect();
 - **Resource Access**: Read static and dynamic resources
 - **Prompt Management**: List and retrieve prompt templates
 - **Completion Support**: Request argument completion suggestions
+- **Sampling & Elicitation**: Respond to server-initiated LLM sampling and user-input requests
 
 ### Advanced Features
 
@@ -233,6 +234,15 @@ $client = Client::builder()
     ->build();
 ```
 
+- **Elicitation Support**: Respond to server requests for user input
+```php
+$elicitationHandler = new ElicitationRequestHandler($myCallback);
+$client = Client::builder()
+    ->setCapabilities(new ClientCapabilities(elicitation: true))
+    ->addRequestHandler($elicitationHandler)
+    ->build();
+```
+
 - **Logging Notifications**: Receive server log messages
 ```php
 $loggingHandler = new LoggingNotificationHandler($myCallback);

ROADMAP.md

@@ -5,7 +5,7 @@ This roadmap is a living document that outlines the planned features and improve
 ## Goals for the First Major Release
 
 - **Server**
-- [ ] Implement full support for elicitations
+- [x] Implement full support for elicitations
 - [ ] Implement OAuth2 authentication for server
 - **Client**
 - [x] Implement client-side support

docs/client.md

@@ -534,6 +534,72 @@ $client = Client::builder()
 > throw new \RuntimeException('Rate limit exceeded');
 > ```
 
+### Elicitation (User Input Requests)
+
+Handle server requests to elicit additional information from the user during tool
+execution. The server sends an `elicitation/create` request describing the fields it
+needs; your callback presents them to the user and returns an `ElicitResult` with one of
+three actions — accept (with the collected content), decline, or cancel:
+
+```php
+use Mcp\Client\Handler\Request\ElicitationRequestHandler;
+use Mcp\Client\Handler\Request\ElicitationCallbackInterface;
+use Mcp\Exception\ElicitationException;
+use Mcp\Schema\ClientCapabilities;
+use Mcp\Schema\Enum\ElicitAction;
+use Mcp\Schema\Request\ElicitRequest;
+use Mcp\Schema\Result\ElicitResult;
+
+class ConsoleElicitationCallback implements ElicitationCallbackInterface
+{
+    public function __invoke(ElicitRequest $request): ElicitResult
+    {
+        echo $request->message.\PHP_EOL;
+
+        // Present $request->requestedSchema->properties to the user and collect input.
+        $content = [];
+        foreach ($request->requestedSchema->properties as $name => $definition) {
+            $answer = readline($definition->title.': ');
+
+            if (false === $answer) {
+                // No input available — let the server know the user cancelled.
+                return new ElicitResult(ElicitAction::Cancel);
+            }
+
+            $content[$name] = $answer;
+        }
+
+        return new ElicitResult(ElicitAction::Accept, $content);
+    }
+}
+
+$client = Client::builder()
+    ->setCapabilities(new ClientCapabilities(elicitation: true))
+    ->addRequestHandler(new ElicitationRequestHandler(new ConsoleElicitationCallback))
+    ->build();
+```
+
+Return `new ElicitResult(ElicitAction::Decline)` when the user refuses to provide the
+information, and `new ElicitResult(ElicitAction::Cancel)` when they dismiss the request.
+Only the `Accept` action carries content.
+
+> [!IMPORTANT]
+> **Error Handling in Elicitation Callbacks:**
+>
+> - **Throw `ElicitationException`** to forward a specific error message to the server
+> - **Any other exception** is logged but returns a generic error to the server
+>
+> ```php
+> // Good: Server receives "No interactive console available" message
+> throw new ElicitationException('No interactive console available');
+>
+> // Bad: Server receives generic "Error while processing elicitation" message
+> throw new \RuntimeException('No interactive console available');
+> ```
+
+See `examples/client/stdio_elicitation.php` for a runnable example against the
+elicitation demo server.
+
 ## Error Handling
 
 The client throws exceptions for various error conditions:

examples/client/stdio_elicitation.php

@@ -0,0 +1,117 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+/**
+ * STDIO Client Elicitation Example.
+ *
+ * This example demonstrates how a client responds to server-initiated
+ * elicitation/create requests. The server's tools ask the user for additional
+ * information mid-execution; the client below auto-fills sensible answers
+ * derived from the requested schema (in a real client you would prompt the user).
+ *
+ * Run against the elicitation demo server:
+ *   php examples/client/stdio_elicitation.php
+ */
+
+require_once __DIR__.'/../../vendor/autoload.php';
+
+use Mcp\Client;
+use Mcp\Client\Handler\Request\ElicitationCallbackInterface;
+use Mcp\Client\Handler\Request\ElicitationRequestHandler;
+use Mcp\Client\Transport\StdioTransport;
+use Mcp\Schema\ClientCapabilities;
+use Mcp\Schema\Content\TextContent;
+use Mcp\Schema\Elicitation\BooleanSchemaDefinition;
+use Mcp\Schema\Elicitation\EnumSchemaDefinition;
+use Mcp\Schema\Elicitation\NumberSchemaDefinition;
+use Mcp\Schema\Elicitation\StringSchemaDefinition;
+use Mcp\Schema\Enum\ElicitAction;
+use Mcp\Schema\Request\ElicitRequest;
+use Mcp\Schema\Result\ElicitResult;
+
+$elicitationRequestHandler = new ElicitationRequestHandler(new class implements ElicitationCallbackInterface {
+    public function __invoke(ElicitRequest $request): ElicitResult
+    {
+        echo "[ELICIT] {$request->message}\n";
+
+        $content = [];
+        foreach ($request->requestedSchema->properties as $name => $definition) {
+            $value = $this->answerFor($definition);
+            $content[$name] = $value;
+            echo "  - {$name}: ".var_export($value, true)."\n";
+        }
+
+        return new ElicitResult(ElicitAction::Accept, $content);
+    }
+
+    private function answerFor(object $definition): mixed
+    {
+        return match (true) {
+            $definition instanceof EnumSchemaDefinition => $definition->default ?? $definition->enum[0],
+            $definition instanceof NumberSchemaDefinition => $definition->default ?? $definition->minimum ?? ($definition->integerOnly ? 1 : 1.0),
+            $definition instanceof BooleanSchemaDefinition => $definition->default ?? true,
+            $definition instanceof StringSchemaDefinition => $definition->default ?? ('date' === $definition->format ? '2026-06-01' : 'example'),
+            default => 'example',
+        };
+    }
+});
+
+$client = Client::builder()
+    ->setClientInfo('STDIO Elicitation Test', '1.0.0')
+    ->setInitTimeout(30)
+    ->setRequestTimeout(120)
+    ->setCapabilities(new ClientCapabilities(elicitation: true))
+    ->addRequestHandler($elicitationRequestHandler)
+    ->build();
+
+$transport = new StdioTransport(
+    command: 'php',
+    args: [__DIR__.'/../server/elicitation/server.php'],
+);
+
+try {
+    echo "Connecting to MCP server...\n";
+    $client->connect($transport);
+
+    $serverInfo = $client->getServerInfo();
+    echo 'Connected to: '.($serverInfo->name ?? 'unknown')."\n\n";
+
+    echo "Calling 'book_restaurant'...\n";
+    $result = $client->callTool(
+        name: 'book_restaurant',
+        arguments: ['restaurantName' => 'The Test Kitchen'],
+    );
+
+    echo "\nResult:\n";
+    foreach ($result->content as $content) {
+        if ($content instanceof TextContent) {
+            echo $content->text."\n";
+        }
+    }
+
+    echo "\nCalling 'confirm_action'...\n";
+    $result = $client->callTool(
+        name: 'confirm_action',
+        arguments: ['actionDescription' => 'Delete all temporary files'],
+    );
+
+    echo "\nResult:\n";
+    foreach ($result->content as $content) {
+        if ($content instanceof TextContent) {
+            echo $content->text."\n";
+        }
+    }
+} catch (Throwable $e) {
+    echo "Error: {$e->getMessage()}\n";
+    echo $e->getTraceAsString()."\n";
+} finally {
+    $client->disconnect();
+}

src/Client/Handler/Request/ElicitationCallbackInterface.php

@@ -0,0 +1,26 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Client\Handler\Request;
+
+use Mcp\Schema\Request\ElicitRequest;
+use Mcp\Schema\Result\ElicitResult;
+
+/**
+ * Contract for callbacks used by ElicitationRequestHandler.
+ *
+ * Implementations present the requested schema to the user and collect their
+ * response when the server sends an elicitation/create request.
+ */
+interface ElicitationCallbackInterface
+{
+    public function __invoke(ElicitRequest $request): ElicitResult;
+}

src/Client/Handler/Request/ElicitationRequestHandler.php

@@ -0,0 +1,68 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Client\Handler\Request;
+
+use Mcp\Exception\ElicitationException;
+use Mcp\Schema\JsonRpc\Error;
+use Mcp\Schema\JsonRpc\Request;
+use Mcp\Schema\JsonRpc\Response;
+use Mcp\Schema\Request\ElicitRequest;
+use Mcp\Schema\Result\ElicitResult;
+use Psr\Log\LoggerInterface;
+use Psr\Log\NullLogger;
+
+/**
+ * Handler for elicitation requests from the server.
+ *
+ * The MCP server may request additional information from the user during tool
+ * execution. This handler wraps a user-provided callback that presents the
+ * requested schema to the user and returns their response.
+ *
+ * @implements RequestHandlerInterface<ElicitResult>
+ *
+ * @author Johannes Wachter <johannes@sulu.io>
+ */
+class ElicitationRequestHandler implements RequestHandlerInterface
+{
+    public function __construct(
+        private readonly ElicitationCallbackInterface $callback,
+        private readonly LoggerInterface $logger = new NullLogger(),
+    ) {
+    }
+
+    public function supports(Request $request): bool
+    {
+        return $request instanceof ElicitRequest;
+    }
+
+    /**
+     * @return Response<ElicitResult>|Error
+     */
+    public function handle(Request $request): Response|Error
+    {
+        \assert($request instanceof ElicitRequest);
+
+        try {
+            $result = $this->callback->__invoke($request);
+
+            return new Response($request->getId(), $result);
+        } catch (ElicitationException $e) {
+            $this->logger->error('Elicitation failed: '.$e->getMessage(), ['exception' => $e]);
+
+            return Error::forInternalError($e->getMessage(), $request->getId());
+        } catch (\Throwable $e) {
+            $this->logger->error('Unexpected error during elicitation', ['exception' => $e]);
+
+            return Error::forInternalError('Error while processing elicitation', $request->getId());
+        }
+    }
+}

src/Exception/ElicitationException.php

@@ -0,0 +1,24 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Exception;
+
+/**
+ * Exception thrown when an elicitation request fails.
+ *
+ * When thrown from an elicitation callback, this exception's message will be
+ * included in the error response sent back to the server.
+ *
+ * @author Johannes Wachter <johannes@sulu.io>
+ */
+final class ElicitationException extends \RuntimeException implements ExceptionInterface
+{
+}

src/JsonRpc/MessageFactory.php

@@ -53,6 +53,7 @@ final class MessageFactory
         Schema\Request\CallToolRequest::class,
         Schema\Request\CompletionCompleteRequest::class,
         Schema\Request\CreateSamplingMessageRequest::class,
+        Schema\Request\ElicitRequest::class,
         Schema\Request\GetPromptRequest::class,
         Schema\Request\InitializeRequest::class,
         Schema\Request\ListPromptsRequest::class,