SQL MCP Server

Instructions

Implementation Reference

• src/tools.ts:134-156 (handler)

  The handler function that creates a Sequelize connection based on db_type and connection_string, optionally blocks write operations, executes the provided SQL query, and returns the results as JSON text.

  async ({db_type, connection_string, query}) => {
    const sequelize = new Sequelize(connection_string, {
      dialect: db_type,
    })
  
    if (!enableWriteOperations) {
      const writeOperations = ['INSERT', 'UPDATE', 'DELETE', 'CREATE', 'ALTER', 'DROP']
      if (writeOperations.some((operation) => query.toUpperCase().includes(operation))) {
        throw new Error('Write operations are not enabled')
      }
    }
  
    const [results] = await sequelize.query(query)
  
    return {
      content: [
        {
          type: 'text',
          text: JSON.stringify(results),
        }
      ],
    }
  },

• src/tools.ts:128-132 (schema)

  Zod input schema defining parameters: db_type (postgres/mysql/sqlite), connection_string, and query.

  inputSchema: {
    db_type: z.enum(['postgres', 'mysql', 'sqlite']), 
    connection_string: z.string(),
    query: z.string(),
  },

• src/tools.ts:123-157 (registration)

  Registration of the 'execute_query' tool using McpServer.registerTool, including title, description, input schema, and handler function.

  server.registerTool(
    'execute_query',
    {
      title: 'Execute Query',
      description: 'Run a query to database',
      inputSchema: {
        db_type: z.enum(['postgres', 'mysql', 'sqlite']), 
        connection_string: z.string(),
        query: z.string(),
      },
    },
    async ({db_type, connection_string, query}) => {
      const sequelize = new Sequelize(connection_string, {
        dialect: db_type,
      })
  
      if (!enableWriteOperations) {
        const writeOperations = ['INSERT', 'UPDATE', 'DELETE', 'CREATE', 'ALTER', 'DROP']
        if (writeOperations.some((operation) => query.toUpperCase().includes(operation))) {
          throw new Error('Write operations are not enabled')
        }
      }
  
      const [results] = await sequelize.query(query)
  
      return {
        content: [
          {
            type: 'text',
            text: JSON.stringify(results),
          }
        ],
      }
    },
  )