MCP MySQL Server

Instructions

Implementation Reference

• src/index.ts:306-344 (handler)

  The primary handler function for the 'mysql_query' tool. It validates input, executes the SQL query using the MySQL pool with optional parameters, handles SELECT (returns rows) and other queries (returns affected rows/insert ID), and returns formatted results or errors.

  private async handleQuery(args: any) {
    if (!this.pool) {
      throw new Error("Not connected to MySQL. Use mysql_connect first.");
    }
  
    const { query, parameters = [] } = args;
    
    if (!query || typeof query !== "string") {
      throw new Error("Query is required and must be a string");
    }
  
    try {
      const [results, fields] = await this.pool.execute(query, parameters);
      
      // Handle different types of results
      if (Array.isArray(results)) {
        return {
          content: [
            {
              type: "text",
              text: `Query executed successfully. ${results.length} rows affected.\n\nResults:\n${JSON.stringify(results, null, 2)}`,
            },
          ],
        };
      } else {
        const resultInfo = results as mysql.ResultSetHeader;
        return {
          content: [
            {
              type: "text",
              text: `Query executed successfully.\nAffected rows: ${resultInfo.affectedRows}\nInserted ID: ${resultInfo.insertId || "N/A"}`,
            },
          ],
        };
      }
    } catch (error) {
      throw new Error(`Query execution failed: ${error instanceof Error ? error.message : String(error)}`);
    }
  }

• src/index.ts:139-155 (schema)

  Defines the JSON Schema for input validation of the mysql_query tool, specifying the required 'query' string and optional 'parameters' array of strings.

  inputSchema: {
    type: "object",
    properties: {
      query: {
        type: "string",
        description: "SQL query to execute",
      },
      parameters: {
        type: "array",
        description: "Parameters for prepared statement (optional)",
        items: {
          type: "string",
        },
      },
    },
    required: ["query"],
  },

• src/index.ts:136-156 (registration)

  Registration of the mysql_query tool in the ListTools handler response, including name, description, and input schema.

  {
    name: "mysql_query",
    description: "Execute a SQL query on the connected MySQL database",
    inputSchema: {
      type: "object",
      properties: {
        query: {
          type: "string",
          description: "SQL query to execute",
        },
        parameters: {
          type: "array",
          description: "Parameters for prepared statement (optional)",
          items: {
            type: "string",
          },
        },
      },
      required: ["query"],
    },
  },

• src/index.ts:251-252 (registration)

  Switch case in the CallToolRequest handler that routes mysql_query invocations to the handleQuery method.

  case "mysql_query":
    return await this.handleQuery(args);