MariaDB MCP Server

Instructions

Implementation Reference

• src/index.ts:124-129 (handler)

  The handler function for the 'list_databases' tool. It executes the SQL query 'SHOW DATABASES' using the executeQuery helper and returns the result rows as a formatted JSON text block.

  case "list_databases": {
    const { rows } = await executeQuery("SHOW DATABASES");
    return {
      content: [{ type: "text", text: JSON.stringify(rows, null, 2) }],
    };
  }

• src/index.ts:82-86 (registration)

  Registration of the 'list_databases' tool in the MCP server's listTools response, including its name, description, and input schema (empty object, no parameters).

  {
    name: "list_databases",
    description: "List all databases",
    inputSchema: { type: "object" },
  },

• src/index.ts:85-85 (schema)

  Input schema for the list_databases tool, specifying an empty object (no input parameters required).

  inputSchema: { type: "object" },

• src/connection.ts:49-114 (helper)

  The executeQuery helper function called by the list_databases handler to perform the actual database query.

  export async function executeQuery(
    sql: string,
    params: any[] = [],
    database?: string
  ): Promise<{ rows: any; fields: mariadb.FieldInfo[] }> {
    console.error(`[Query] Executing: ${sql}`);
    // Create connection pool if not already created
    if (!pool) {
      console.error("[Setup] Connection pool not found, creating a new one");
      pool = createConnectionPool();
    }
    try {
      // Get connection from pool
      if (connection) {
        console.error("[Query] Reusing existing connection");
      } else {
        console.error("[Query] Creating new connection");
        connection = await pool.getConnection();
      }
  
      // Use specific database if provided
      if (database) {
        console.error(`[Query] Using database: ${database}`);
        await connection.query(`USE \`${database}\``);
      }
      if (!isAlloowedQuery(sql)) {
        throw new Error("Query not allowed");
      }
      // Execute query with timeout
      const [rows, fields] = await connection.query({
        metaAsArray: true,
        namedPlaceholders: true,
        sql,
        ...params,
        timeout: DEFAULT_TIMEOUT,
      });
  
      // Apply row limit if result is an array
      const limitedRows =
        Array.isArray(rows) && rows.length > DEFAULT_ROW_LIMIT
          ? rows.slice(0, DEFAULT_ROW_LIMIT)
          : rows;
  
      // Log result summary
      console.error(
        `[Query] Success: ${
          Array.isArray(rows) ? rows.length : 1
        } rows returned with ${JSON.stringify(params)}`
      );
  
      return { rows: limitedRows, fields };
    } catch (error) {
      if (connection) {
        connection.release();
        console.error("[Query] Connection released with error");
      }
      console.error("[Error] Query execution failed:", error);
      throw error;
    } finally {
      // Release connection back to pool
      if (connection) {
        connection.release();
        console.error("[Query] Connection released");
      }
    }
  }