describe_table

Instructions

Implementation Reference

• src/index.ts:319-328 (handler)

  The handler for the 'describe_table' tool: validates the table name, then queries PRAGMA table_info, index_list, and foreign_key_list to return the table schema.

  case 'describe_table': {
    const { table_name } = toolArgs as { table_name: string };
    validateTableName(table_name);
    const columns = db.all(`PRAGMA table_info("${table_name}")`);
    const indexes = db.all(`PRAGMA index_list("${table_name}")`);
    const foreignKeys = db.all(`PRAGMA foreign_key_list("${table_name}")`);
    return {
      content: [{ type: 'text', text: JSON.stringify({ columns, indexes, foreign_keys: foreignKeys }, null, 2) }],
    };
  }

• src/index.ts:251-261 (schema)

  The tool registration/schema definition: defines 'describe_table' with a required 'table_name' string parameter.

  {
    name: 'describe_table',
    description: 'Get the schema of a table: columns, types, constraints, indexes, and foreign keys.',
    inputSchema: {
      type: 'object' as const,
      properties: {
        table_name: { type: 'string', description: 'Name of the table to describe' },
      },
      required: ['table_name'],
    },
  },

• src/index.ts:197-274 (registration)

  Registration of all tools via ListToolsRequestSchema handler, including 'describe_table' in the tools list.

  server.setRequestHandler(ListToolsRequestSchema, async () => ({
    tools: [
      {
        name: 'read_query',
        description: 'Execute a read-only SQL query (SELECT, WITH/CTE, or EXPLAIN). Use this for fetching data.',
        inputSchema: {
          type: 'object' as const,
          properties: {
            query: { type: 'string', description: 'The SELECT SQL query to execute' },
          },
          required: ['query'],
        },
      },
      {
        name: 'write_query',
        description: 'Execute a data modification query (INSERT, UPDATE, DELETE, REPLACE). Returns affected row count.',
        inputSchema: {
          type: 'object' as const,
          properties: {
            query: { type: 'string', description: 'The SQL modification query to execute' },
          },
          required: ['query'],
        },
      },
      {
        name: 'create_table',
        description: 'Create a new table in the database with a full CREATE TABLE SQL statement.',
        inputSchema: {
          type: 'object' as const,
          properties: {
            query: { type: 'string', description: 'CREATE TABLE SQL statement' },
          },
          required: ['query'],
        },
      },
      {
        name: 'drop_table',
        description: 'Drop (delete) a table from the database. This action is irreversible.',
        inputSchema: {
          type: 'object' as const,
          properties: {
            table_name: { type: 'string', description: 'Name of the table to drop' },
          },
          required: ['table_name'],
        },
      },
      {
        name: 'list_tables',
        description: 'List all user-created tables in the database.',
        inputSchema: {
          type: 'object' as const,
          properties: {},
        },
      },
      {
        name: 'describe_table',
        description: 'Get the schema of a table: columns, types, constraints, indexes, and foreign keys.',
        inputSchema: {
          type: 'object' as const,
          properties: {
            table_name: { type: 'string', description: 'Name of the table to describe' },
          },
          required: ['table_name'],
        },
      },
      {
        name: 'append_insight',
        description: 'Add a business insight to the insights memo resource. Useful for recording observations from analysis.',
        inputSchema: {
          type: 'object' as const,
          properties: {
            insight: { type: 'string', description: 'The business insight to record' },
          },
          required: ['insight'],
        },
      },
    ],
  }));

• src/index.ts:30-34 (helper)

  Validation helper used by the describe_table handler to ensure the table name is a valid SQL identifier.

  function validateTableName(name: string): void {
    if (!VALID_IDENTIFIER.test(name)) {
      throw new McpError(ErrorCode.InvalidParams, `Invalid table name: "${name}". Use only letters, numbers, and underscores.`);
    }
  }