MCP Server Boilerplate

#!/usr/bin/env node import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js"; import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js"; import { z } from "zod"; import { MongoClient, Db, Collection } from "mongodb"; const server = new McpServer({ name: "mongo-mcp", version: "1.0.0", }); let mongoClient: MongoClient | null = null; let databases: Map<string, Db> = new Map(); function truncateForOutput(obj: unknown, maxOutputLength: number = 25000): unknown { const estimatedSize = JSON.stringify(obj).length; if (estimatedSize <= maxOutputLength) { return obj; } function truncateValue(value: unknown): unknown { if (typeof value === "string" && value.length > 200) { const truncated = value.slice(0, 200); const remaining = value.length - 200; return `${truncated}...${remaining} more characters`; } if (Array.isArray(value)) { if (value.length <= 1) { return value.map((item) => truncateValue(item)); } const firstItem = truncateValue(value[0]); const remaining = value.length - 1; return [firstItem, `...${remaining} more items`]; } if (typeof value === "object" && value !== null) { const keys = Object.keys(value); if (keys.length <= 200) { const result: Record<string, unknown> = {}; for (const key of keys) { result[key] = truncateValue((value as Record<string, unknown>)[key]); } return result; } const result: Record<string, unknown> = {}; const firstKeys = keys.slice(0, 200); for (const key of firstKeys) { result[key] = truncateValue((value as Record<string, unknown>)[key]); } const remaining = keys.length - 200; result[`...${remaining} more properties`] = "..."; return result; } return value; } return truncateValue(obj); } function formatJsonOutput(data: unknown): string { const truncatedData = truncateForOutput(data); let outputText = JSON.stringify(truncatedData, null, 2); outputText = outputText.replace( /"\.\.\.(\d+) more items"/g, "...$1 more items" ); outputText = outputText.replace( /"\.\.\.(\d+) more properties": "\.\.\.?"/g, "...$1 more properties" ); return outputText; } function getMongoUri(): string { const uri = process.env.MONGODB_URI; if (!uri) { throw new Error("MONGODB_URI environment variable is not set"); } return uri; } async function ensureConnection(dbName: string): Promise<Db> { if (!mongoClient) { const uri = getMongoUri(); mongoClient = new MongoClient(uri); await mongoClient.connect(); } if (!databases.has(dbName)) { databases.set(dbName, mongoClient.db(dbName)); } return databases.get(dbName)!; } server.tool( "mongo-create-document", "Create a new document in a MongoDB collection", { database: z.string().describe("Database name"), collection: z.string().describe("Collection name"), document: z.record(z.any()).describe("Document to insert as JSON object"), }, async ({ database: dbName, collection: collectionName, document }) => { try { const db = await ensureConnection(dbName); const collection: Collection = db.collection(collectionName); const result = await collection.insertOne(document); return { content: [ { type: "text", text: `Document created successfully with ID: ${result.insertedId}`, }, ], }; } catch (error) { throw new Error(`Failed to create document: ${error instanceof Error ? error.message : 'Unknown error'}`); } } ); server.tool( "mongo-find-documents", "Query documents from a MongoDB collection", { database: z.string().describe("Database name"), collection: z.string().describe("Collection name"), filter: z.record(z.any()).optional().describe("Query filter as JSON object (optional)"), limit: z.number().optional().describe("Maximum number of documents to return (optional)"), }, async ({ database: dbName, collection: collectionName, filter = {}, limit }) => { try { const db = await ensureConnection(dbName); const collection: Collection = db.collection(collectionName); let cursor = collection.find(filter); if (limit) { cursor = cursor.limit(limit); } const documents = await cursor.toArray(); const formattedOutput = formatJsonOutput(documents); return { content: [ { type: "text", text: `Found ${documents.length} document(s):\n\n${formattedOutput}`, }, ], }; } catch (error) { throw new Error(`Failed to find documents: ${error instanceof Error ? error.message : 'Unknown error'}`); } } ); server.tool( "mongo-update-document", "Update documents in a MongoDB collection", { database: z.string().describe("Database name"), collection: z.string().describe("Collection name"), filter: z.record(z.any()).describe("Query filter to match documents to update"), update: z.record(z.any()).describe("Update operations as JSON object"), updateMany: z.boolean().optional().describe("Whether to update multiple documents (default: false)"), }, async ({ database: dbName, collection: collectionName, filter, update, updateMany = false }) => { try { const db = await ensureConnection(dbName); const collection: Collection = db.collection(collectionName); const result = updateMany ? await collection.updateMany(filter, update) : await collection.updateOne(filter, update); return { content: [ { type: "text", text: `Update operation completed. Matched: ${result.matchedCount}, Modified: ${result.modifiedCount}`, }, ], }; } catch (error) { throw new Error(`Failed to update document(s): ${error instanceof Error ? error.message : 'Unknown error'}`); } } ); server.tool( "mongo-delete-document", "Delete documents from a MongoDB collection", { database: z.string().describe("Database name"), collection: z.string().describe("Collection name"), filter: z.record(z.any()).describe("Query filter to match documents to delete"), deleteMany: z.boolean().optional().describe("Whether to delete multiple documents (default: false)"), }, async ({ database: dbName, collection: collectionName, filter, deleteMany = false }) => { try { const db = await ensureConnection(dbName); const collection: Collection = db.collection(collectionName); const result = deleteMany ? await collection.deleteMany(filter) : await collection.deleteOne(filter); return { content: [ { type: "text", text: `Delete operation completed. Deleted ${result.deletedCount} document(s)`, }, ], }; } catch (error) { throw new Error(`Failed to delete document(s): ${error instanceof Error ? error.message : 'Unknown error'}`); } } ); server.tool( "mongo-aggregate", "Execute aggregation pipeline on a MongoDB collection", { database: z.string().describe("Database name"), collection: z.string().describe("Collection name"), pipeline: z.array(z.record(z.any())).describe("Aggregation pipeline as array of stage objects"), }, async ({ database: dbName, collection: collectionName, pipeline }) => { try { const db = await ensureConnection(dbName); const collection: Collection = db.collection(collectionName); const documents = await collection.aggregate(pipeline).toArray(); const formattedOutput = formatJsonOutput(documents); return { content: [ { type: "text", text: `Aggregation returned ${documents.length} document(s):\n\n${formattedOutput}`, }, ], }; } catch (error) { throw new Error(`Failed to execute aggregation: ${error instanceof Error ? error.message : 'Unknown error'}`); } } ); server.tool( "mongo-count-documents", "Count documents in a MongoDB collection", { database: z.string().describe("Database name"), collection: z.string().describe("Collection name"), filter: z.record(z.any()).optional().describe("Query filter as JSON object (optional)"), }, async ({ database: dbName, collection: collectionName, filter = {} }) => { try { const db = await ensureConnection(dbName); const collection: Collection = db.collection(collectionName); const count = await collection.countDocuments(filter); return { content: [ { type: "text", text: `Found ${count} document(s) matching the filter`, }, ], }; } catch (error) { throw new Error(`Failed to count documents: ${error instanceof Error ? error.message : 'Unknown error'}`); } } ); server.tool( "mongo-list-collections", "List all collections in a MongoDB database", { database: z.string().describe("Database name"), }, async ({ database: dbName }) => { try { const db = await ensureConnection(dbName); const collections = await db.listCollections().toArray(); const collectionNames = collections.map(col => col.name); return { content: [ { type: "text", text: `Collections in database '${dbName}':\n${collectionNames.join('\n')}`, }, ], }; } catch (error) { throw new Error(`Failed to list collections: ${error instanceof Error ? error.message : 'Unknown error'}`); } } ); async function main() { try { const transport = new StdioServerTransport(); await server.connect(transport); console.error("MongoDB MCP Server running..."); } catch (error) { console.error("Error starting server:", error); process.exit(1); } } main().catch(console.error);