fix: tweak the connect tool arguments to instruct the model to prefer preconfigured connection string

Author: nirinchev

src/server.ts

@@ -5,6 +5,7 @@ import { AtlasTools } from "./tools/atlas/tools.js";
 import { MongoDbTools } from "./tools/mongodb/tools.js";
 import logger, { initializeLogger } from "./logger.js";
 import { mongoLogId } from "mongodb-log-writer";
+import config from "./config.js";
 
 export class Server {
     public readonly session: Session;
@@ -19,6 +20,7 @@ export class Server {
         this.mcpServer.server.registerCapabilities({ logging: {} });
 
         this.registerTools();
+        this.registerResources();
 
         await initializeLogger(this.mcpServer);
 
@@ -37,4 +39,26 @@ export class Server {
             new tool(this.session).register(this.mcpServer);
         }
     }
+
+    private registerResources() {
+        if (config.connectionString) {
+            this.mcpServer.resource(
+                "connection-string",
+                "config://connection-string",
+                {
+                    description: "Preconfigured connection string that will be used as a default in the `connect` tool",
+                },
+                (uri) => {
+                    return {
+                        contents: [
+                            {
+                                text: `Preconfigured connection string: ${config.connectionString}`,
+                                uri: uri.href,
+                            },
+                        ],
+                    };
+                }
+            );
+        }
+    }
 }

src/tools/mongodb/metadata/connect.ts

@@ -9,19 +9,32 @@ export class ConnectTool extends MongoDBToolBase {
     protected name = "connect";
     protected description = "Connect to a MongoDB instance";
     protected argsShape = {
-        connectionStringOrClusterName: z
-            .string()
+        options: z
+            .array(
+                z
+                    .union([
+                        z.object({
+                            connectionString: z
+                                .string()
+                                .describe("MongoDB connection string (in the mongodb:// or mongodb+srv:// format)"),
+                        }),
+                        z.object({
+                            clusterName: z.string().describe("MongoDB cluster name"),
+                        }),
+                    ])
+                    .optional()
+            )
             .optional()
-            .describe("MongoDB connection string (in the mongodb:// or mongodb+srv:// format) or cluster name"),
+            .describe(
+                "Options for connecting to MongoDB. If not provided, the connection string from the config://connection-string resource will be used. If the user hasn't specified Atlas cluster name or a connection string explicitly and the `config://connection-string` resource is present, always invoke this with no arguments."
+            ),
     };
 
     protected operationType: OperationType = "metadata";
 
-    protected async execute({
-        connectionStringOrClusterName,
-    }: ToolArgs<typeof this.argsShape>): Promise<CallToolResult> {
-        connectionStringOrClusterName ??= config.connectionString;
-        if (!connectionStringOrClusterName) {
+    protected async execute({ options: optionsArr }: ToolArgs<typeof this.argsShape>): Promise<CallToolResult> {
+        const options = optionsArr?.[0];
+        if (!options && !config.connectionString) {
             return {
                 content: [
                     { type: "text", text: "No connection details provided." },
@@ -36,11 +49,10 @@ export class ConnectTool extends MongoDBToolBase {
 
         let connectionString: string;
 
-        if (
-            connectionStringOrClusterName.startsWith("mongodb://") ||
-            connectionStringOrClusterName.startsWith("mongodb+srv://")
-        ) {
-            connectionString = connectionStringOrClusterName;
+        if (!options) {
+            connectionString = config.connectionString!;
+        } else if ("connectionString" in options) {
+            connectionString = options.connectionString;
         } else {
             // TODO: https://github.com/mongodb-js/mongodb-mcp-server/issues/19
             // We don't support connecting via cluster name since we'd need to obtain the user credentials