Add Prompts support for MCP Server

Author: yasmewad

codegen/plugins/server-codegen/src/main/java/software/amazon/smithy/java/codegen/server/ServiceJavaSymbolProvider.java

@@ -59,10 +59,10 @@ public Symbol operationShape(OperationShape operationShape) {
 
     @Override
     public Symbol serviceShape(ServiceShape serviceShape) {
-        return getServerJavaClassSymbol();
+        return getServerJavaClassSymbol(serviceShape);
     }
 
-    private Symbol getServerJavaClassSymbol() {
+    private Symbol getServerJavaClassSymbol(ServiceShape serviceShape) {
         return Symbol.builder()
                 .name(serviceName)
                 .putProperty(SymbolProperties.IS_PRIMITIVE, false)

examples/mcp-server/build.gradle.kts

@@ -10,6 +10,7 @@ dependencies {
     val smithyJavaVersion: String by project
 
     smithyBuild("software.amazon.smithy.java:plugins:$smithyJavaVersion")
+    implementation("software.amazon.smithy.java:mcp-traits:$smithyJavaVersion")
     implementation("software.amazon.smithy.java:mcp-server:$smithyJavaVersion")
     implementation("software.amazon.smithy.java:server-proxy:$smithyJavaVersion")
     implementation("software.amazon.smithy.java:server-netty:$smithyJavaVersion")

examples/mcp-server/smithy-build.json

@@ -6,7 +6,7 @@
       "service": "smithy.example.mcp#EmployeeService",
       "namespace": "software.amazon.smithy.java.example.server.mcp",
       "headerFile": "license.txt",
-      "runtimeTraits": ["smithy.api#documentation", "smithy.api#examples" ]
+      "runtimeTraits": ["smithy.api#documentation", "smithy.api#examples", "amazon.smithy.llm#prompts" ]
     }
   }
 }

examples/mcp-server/src/main/resources/software/amazon/smithy/java/example/server/mcp/main.smithy

@@ -3,30 +3,58 @@ $version: "2"
 namespace smithy.example.mcp
 
 use aws.protocols#restJson1
+use amazon.smithy.llm#prompts
 
 @restJson1
+@prompts({
+    get_employee_info: {
+        description: "Retrieve detailed information about an employee by their login ID"
+        template: "Get employee details for login ID {{loginId}}. This will return the employee's name and manager information."
+        arguments: GetEmployeeDetailsInput
+        preferWhen: "User needs to look up employee information, find who someone reports to, or verify employee details"
+    }
+    get_coding_stats: {
+        description: "Retrieve coding statistics and commit information for an employee"
+        template: "Get coding statistics for employee {{login}}. This returns commit counts by programming language."
+        arguments: GetCodingStatisticsInput
+        preferWhen: "User wants to analyze developer productivity, review coding activity, or understand technology usage patterns"
+    }
+    employee_lookup: {
+        description: "General employee lookup and information retrieval service"
+        template: "This service provides employee information including personal details and coding statistics. Use get_employee_info for basic details or get_coding_stats for development metrics."
+        preferWhen: "User needs any employee-related information or wants to understand available employee data"
+    }
+})
 service EmployeeService {
     operations: [
         GetEmployeeDetails
         GetCodingStatistics
     ]
 }
 
+@prompts({
+    get_employee_info_operation: {
+        description: "Retrieve detailed information about an employee by their login ID on the operation."
+        template: "Get employee details for login ID {{loginId}}. This will return the employee's name and manager information."
+        arguments: GetEmployeeDetailsInput
+        preferWhen: "User needs to look up employee information, find who someone reports to, or verify employee details"
+    }
+})
 @documentation("Get employee information by login id")
 @http(method: "POST", uri: "/get-employee-details")
 operation GetEmployeeDetails {
-    input := {
-        @required
-        loginId: LoginId
-    }
-
+    input: GetEmployeeDetailsInput
     output: Employee
-
     errors: [
         NoSuchUserException
     ]
 }
 
+structure GetEmployeeDetailsInput {
+    @required
+    loginId: LoginId
+}
+
 structure Employee {
     @documentation("Name of the employee.")
     name: String
@@ -38,14 +66,15 @@ structure Employee {
 @documentation("Get coding statistics of an employee.")
 @http(method: "POST", uri: "/get-coding-statistics")
 operation GetCodingStatistics {
-    input := {
-        @required
-        login: LoginId
-    }
-
+    input: GetCodingStatisticsInput
     output: CodingStatistics
 }
 
+structure GetCodingStatisticsInput {
+    @required
+    login: LoginId
+}
+
 @documentation("Coding statistics of a user.")
 structure CodingStatistics {
     @documentation("Map of number of commits made per language. This can be empty or null.")

mcp/mcp-cli/src/main/java/software/amazon/smithy/java/mcp/cli/commands/StartServer.java

@@ -164,7 +164,11 @@ public void execute(ExecutionContext context) throws IOException {
             }
 
             this.mcpServer =
-                    (McpServer) McpServer.builder().stdio().addServices(services).name("smithy-mcp-server").build();
+                    (McpServer) McpServer.builder()
+                            .stdio()
+                            .addServices(services)
+                            .name("smithy-mcp-server")
+                            .build();
             mcpServer.start();
             awaitCompletion = mcpServer::awaitCompletion;
             shutdownMethod = mcpServer::shutdown;
@@ -185,6 +189,7 @@ public void execute(ExecutionContext context) throws IOException {
     private static Service bundleToService(SmithyModeledBundleConfig bundleConfig) {
         Service service =
                 McpBundles.getService(ConfigUtils.getMcpBundle(bundleConfig.getName()));
+
         if (bundleConfig.hasAllowListedTools() || bundleConfig.hasBlockListedTools()) {
             var filter = OperationFilters.allowList(bundleConfig.getAllowListedTools())
                     .and(OperationFilters.blockList(bundleConfig.getBlockListedTools()));

mcp/mcp-schemas/model/main.smithy

@@ -182,3 +182,68 @@ structure TextContent {
 
     text: String
 }
+
+structure ListPromptsResult {
+    prompts: PromptInfoList
+}
+
+list PromptInfoList {
+    member: PromptInfo
+}
+
+structure PromptArgument {
+    @required
+    name: String
+
+    description: String
+
+    required: Boolean
+}
+
+list PromptArgumentList {
+    member: PromptArgument
+}
+
+structure PromptInfo {
+    @required
+    name: String
+
+    title: String
+
+    description: String
+
+    arguments: PromptArgumentList
+}
+
+structure PromptMessageContent {
+    @required
+    type: PromptMessageContentType = "text"
+
+    text: String
+}
+
+enum PromptMessageContentType {
+    TEXT = "text"
+}
+
+structure PromptMessage {
+    @required
+    role: String
+
+    @required
+    content: PromptMessageContent
+}
+
+enum PromptRole {
+    USER = "user"
+    ASSISTANT = "assistant"
+}
+
+list PromptMessageList {
+    member: PromptMessage
+}
+
+structure GetPromptResult {
+    description: String
+    messages: PromptMessageList
+}

mcp/mcp-server/src/main/java/software/amazon/smithy/java/mcp/server/McpServer.java

@@ -41,7 +41,9 @@
 import software.amazon.smithy.java.mcp.model.JsonRpcErrorResponse;
 import software.amazon.smithy.java.mcp.model.JsonRpcRequest;
 import software.amazon.smithy.java.mcp.model.JsonRpcResponse;
+import software.amazon.smithy.java.mcp.model.ListPromptsResult;
 import software.amazon.smithy.java.mcp.model.ListToolsResult;
+import software.amazon.smithy.java.mcp.model.Prompts;
 import software.amazon.smithy.java.mcp.model.ServerInfo;
 import software.amazon.smithy.java.mcp.model.TextContent;
 import software.amazon.smithy.java.mcp.model.ToolInfo;
@@ -66,6 +68,8 @@ public final class McpServer implements Server {
             .build();
 
     private final Map<String, Tool> tools;
+    private final Map<String, Prompt> prompts;
+    private final PromptProcessor promptProcessor;
     private final Thread listener;
     private final InputStream is;
     private final OutputStream os;
@@ -75,6 +79,8 @@ public final class McpServer implements Server {
 
     McpServer(McpServerBuilder builder) {
         this.tools = createTools(builder.serviceList);
+        this.prompts = PromptLoader.loadPrompts(builder.serviceList);
+        this.promptProcessor = new PromptProcessor();
         this.is = builder.is;
         this.os = builder.os;
         this.name = builder.name;
@@ -113,12 +119,31 @@ private void handleRequest(JsonRpcRequest req) {
                         InitializeResult.builder()
                                 .capabilities(Capabilities.builder()
                                         .tools(Tools.builder().listChanged(true).build())
+                                        .prompts(Prompts.builder().listChanged(true).build())
                                         .build())
                                 .serverInfo(ServerInfo.builder()
                                         .name(name)
                                         .version("1.0.0")
                                         .build())
                                 .build());
+                case "prompts/list" -> writeResponse(req.getId(),
+                        ListPromptsResult.builder()
+                                .prompts(prompts.values().stream().map(Prompt::promptInfo).toList())
+                                .build());
+                case "prompts/get" -> {
+                    var promptName = req.getParams().getMember("name").asString();
+                    var promptArguments = req.getParams().getMember("arguments");
+
+                    var prompt = prompts.get(promptName);
+
+                    if (prompt == null) {
+                        internalError(req, new RuntimeException("Prompt not found: " + promptName));
+                        return;
+                    }
+
+                    var result = promptProcessor.buildPromptResult(prompt, promptArguments);
+                    writeResponse(req.getId(), result);
+                }
                 case "tools/list" -> writeResponse(req.getId(),
                         ListToolsResult.builder().tools(tools.values().stream().map(Tool::toolInfo).toList()).build());
                 case "tools/call" -> {

mcp/mcp-server/src/main/java/software/amazon/smithy/java/mcp/server/McpServerBuilder.java

@@ -13,6 +13,7 @@
 import java.util.Objects;
 import software.amazon.smithy.java.server.Server;
 import software.amazon.smithy.java.server.Service;
+import software.amazon.smithy.model.Model;
 import software.amazon.smithy.utils.SmithyUnstableApi;
 
 @SmithyUnstableApi
@@ -22,6 +23,7 @@ public final class McpServerBuilder {
     OutputStream os;
     List<Service> serviceList = new ArrayList<>();
     List<McpServerProxy> proxyList = new ArrayList<>();
+    List<Model> modelList = new ArrayList<>();
     String name;
 
     McpServerBuilder() {}

mcp/mcp-server/src/main/java/software/amazon/smithy/java/mcp/server/Prompt.java

@@ -0,0 +1,10 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.java.mcp.server;
+
+import software.amazon.smithy.java.mcp.model.PromptInfo;
+
+public record Prompt(PromptInfo promptInfo, String promptTemplate) {}