mongo-find-documents

Instructions

Implementation Reference

• src/index.ts:140-165 (handler)

  The handler function that executes the mongo-find-documents tool: connects to MongoDB database, finds documents using the provided filter and optional limit, formats the output as truncated JSON, and returns it in the MCP response format.

  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'}`);
    }
  }

• src/index.ts:134-139 (schema)

  Zod schema for the tool's input parameters: required database and collection names, optional filter object and limit number.

  {
    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)"),
  },

• src/index.ts:131-166 (registration)

  Registration of the "mongo-find-documents" tool with the MCP server, specifying name, description, input schema, and inline handler function.

  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'}`);
      }
    }
  );

• src/index.ts:88-100 (helper)

  Helper function to ensure a MongoDB connection and database instance is available, used by the tool handler.

  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)!;
  }

• src/index.ts:64-78 (helper)

  Helper function to format and clean up truncated JSON output for the tool response, called by the handler.

  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;
  }