Add validation for prompt name uniqueness across the MCP Server as well as in a single smithy model at build time. (#833)

Author: yasmewad

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

@@ -19,7 +19,7 @@ use smithy.ai#prompts
         arguments: GetCodingStatisticsInput
         preferWhen: "User wants to analyze developer productivity, review coding activity, or understand technology usage patterns"
     }
-    employee_lookup: {
+    Test_employee: {
         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"

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

@@ -5,6 +5,8 @@
 
 package software.amazon.smithy.java.mcp.server;
 
+import static software.amazon.smithy.java.mcp.server.PromptLoader.normalize;
+
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.PrintWriter;
@@ -146,7 +148,7 @@ private void handleRequest(JsonRpcRequest req) {
                     var promptName = req.getParams().getMember("name").asString();
                     var promptArguments = req.getParams().getMember("arguments");
 
-                    var prompt = prompts.get(promptName);
+                    var prompt = prompts.get(normalize(promptName));
 
                     if (prompt == null) {
                         internalError(req, new RuntimeException("Prompt not found: " + promptName));

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

@@ -54,7 +54,7 @@ public static Map<String, Prompt> loadPrompts(Collection<Service> services) {
 
             });
             for (Map.Entry<String, PromptTemplateDefinition> entry : promptDefinitions.entrySet()) {
-                var promptName = entry.getKey().toLowerCase();
+                var promptName = entry.getKey();
                 var promptTemplateDefinition = entry.getValue();
                 var templateString = promptTemplateDefinition.getTemplate();
 
@@ -76,8 +76,20 @@ public static Map<String, Prompt> loadPrompts(Collection<Service> services) {
                                 : List.of())
                         .build();
 
+                var normalizedName = normalize(promptName);
+
+                if (prompts.containsKey(normalizedName)) {
+                    var existingPrompt = prompts.get(normalizedName);
+                    throw new RuntimeException(String.format(
+                            "Duplicate normalized prompt name '%s' found. " +
+                                    "Original name '%s' conflicts with previously registered name '%s'.",
+                            normalizedName,
+                            promptName,
+                            existingPrompt.promptInfo().getName()));
+                }
+
                 prompts.put(
-                        promptName,
+                        normalizedName,
                         new Prompt(promptInfo, finalTemplateString));
             }
         }
@@ -118,4 +130,8 @@ public static List<PromptArgument> convertArgumentShapeToPromptArgument(Schema a
 
         return promptArguments;
     }
+
+    public static String normalize(String promptName) {
+        return promptName.toLowerCase();
+    }
 }

mcp/mcp-server/src/test/java/software/amazon/smithy/java/mcp/server/McpServerTest.java

@@ -395,6 +395,16 @@ void testPromptsList() {
         assertEquals("search_users", servicePromptMap.get("name").asString());
         assertEquals("Test Template", servicePromptMap.get("description").asString());
         assertTrue(servicePromptMap.get("arguments").asList().isEmpty());
+
+        var promptNames = prompts.stream()
+                .map(p -> p.asStringMap().get("name").asString())
+                .toList();
+        assertTrue(promptNames.contains("search_users"));
+        assertTrue(promptNames.contains("perform_operation"));
+
+        for (String name : promptNames) {
+            assertEquals(name.toLowerCase(), name, "Prompt name should be normalized to lowercase: " + name);
+        }
     }
 
     @Test
@@ -430,6 +440,76 @@ void testPromptsGetWithValidPrompt() {
         assertEquals("Search for if many results expected.", content.get("text").asString());
     }
 
+    @Test
+    void testPromptsGetWithDifferentCasing() {
+        server = McpServer.builder()
+                .input(input)
+                .output(output)
+                .addService("test-mcp",
+                        ProxyService.builder()
+                                .service(ShapeId.from("smithy.test#TestService"))
+                                .proxyEndpoint("http://localhost")
+                                .model(MODEL)
+                                .build())
+                .build();
+
+        server.start();
+
+        // Test with uppercase prompt name
+        write("prompts/get",
+                Document.of(Map.of(
+                        "name",
+                        Document.of("SEARCH_USERS"))));
+        var response = read();
+        var result = response.getResult().asStringMap();
+
+        assertEquals("Test Template", result.get("description").asString());
+        var messages = result.get("messages").asList();
+        assertEquals(1, messages.size());
+
+        var message = messages.get(0).asStringMap();
+        assertEquals("user", message.get("role").asString());
+        var content = message.get("content").asStringMap();
+        assertEquals("text", content.get("type").asString());
+        assertEquals("Search for if many results expected.", content.get("text").asString());
+
+        // Test with mixed case prompt name
+        write("prompts/get",
+                Document.of(Map.of(
+                        "name",
+                        Document.of("Search_Users"))));
+        response = read();
+        result = response.getResult().asStringMap();
+
+        assertEquals("Test Template", result.get("description").asString());
+        messages = result.get("messages").asList();
+        assertEquals(1, messages.size());
+
+        message = messages.get(0).asStringMap();
+        assertEquals("user", message.get("role").asString());
+        content = message.get("content").asStringMap();
+        assertEquals("text", content.get("type").asString());
+        assertEquals("Search for if many results expected.", content.get("text").asString());
+
+        // Test with perform_operation prompt in different case
+        write("prompts/get",
+                Document.of(Map.of(
+                        "name",
+                        Document.of("PERFORM_OPERATION"))));
+        response = read();
+        result = response.getResult().asStringMap();
+
+        assertEquals("perform operation", result.get("description").asString());
+        messages = result.get("messages").asList();
+        assertEquals(1, messages.size());
+
+        message = messages.get(0).asStringMap();
+        assertEquals("user", message.get("role").asString());
+        content = message.get("content").asStringMap();
+        assertEquals("text", content.get("type").asString());
+        assertEquals("use tool TestOperation with some information.", content.get("text").asString());
+    }
+
     @Test
     void testPromptsGetWithInvalidPrompt() {
         server = McpServer.builder()
@@ -452,6 +532,15 @@ void testPromptsGetWithInvalidPrompt() {
         var response = read();
         assertNotNull(response.getError());
         assertTrue(response.getError().getMessage().contains("Prompt not found: nonexistent_prompt"));
+
+        // Test with invalid prompt in different case - should still fail
+        write("prompts/get",
+                Document.of(Map.of(
+                        "name",
+                        Document.of("NONEXISTENT_PROMPT"))));
+        response = read();
+        assertNotNull(response.getError());
+        assertTrue(response.getError().getMessage().contains("Prompt not found: NONEXISTENT_PROMPT"));
     }
 
     @Test