describe_all_tables

Instructions

Implementation Reference

• src/tools/describe-all-tables.ts:21-87 (handler)

  The handler function that executes the describe_all_tables tool logic. It validates input, queries information_schema.COLUMNS for all tables in the database, groups columns by table, and returns formatted output.

  export function createDescribeAllTablesHandler(runner: QueryRunner) {
    return async ({ database }: { database?: string }) => {
      if (database) {
        const dbValidation = validateIdentifier(database, 'Database');
        if (!dbValidation.valid) {
          return {
            isError: true as const,
            content: [{ type: 'text' as const, text: dbValidation.message! }],
          };
        }
      }
  
      try {
        return await runner.withConnection(async (query) => {
          const db = await resolveDatabase(query, database);
          if (!db) {
            return {
              isError: true as const,
              content: [
                {
                  type: 'text' as const,
                  text: 'Error: No database selected. Specify a database name or set MYSQL_DATABASE.',
                },
              ],
            };
          }
  
          const sql = `SELECT TABLE_NAME, COLUMN_NAME, COLUMN_TYPE, IS_NULLABLE, COLUMN_KEY, COLUMN_DEFAULT, EXTRA, COLUMN_COMMENT FROM information_schema.COLUMNS WHERE TABLE_SCHEMA = ${quoteStringValue(db)} ORDER BY TABLE_NAME, ORDINAL_POSITION`;
          const [rows] = await query(sql);
          const typedRows = rows as Record<string, unknown>[];
  
          if (typedRows.length === 0) {
            return { content: [{ type: 'text' as const, text: '(no tables)' }] };
          }
  
          const tableMap = new Map<string, string[]>();
          for (const r of typedRows) {
            const tableName = String(r.TABLE_NAME);
            const line = formatColumn({
              name: String(r.COLUMN_NAME),
              type: String(r.COLUMN_TYPE),
              nullable: r.IS_NULLABLE === 'YES',
              key: String(r.COLUMN_KEY ?? ''),
              defaultValue: r.COLUMN_DEFAULT,
              extra: String(r.EXTRA ?? ''),
              comment: String(r.COLUMN_COMMENT ?? ''),
            });
            if (!tableMap.has(tableName)) {
              tableMap.set(tableName, []);
            }
            tableMap.get(tableName)!.push(line);
          }
  
          const parts = Array.from(tableMap.entries()).map(([table, lines]) => `${table}:\n${lines.join('\n')}`);
  
          return {
            content: [{ type: 'text' as const, text: parts.join('\n\n') }],
          };
        });
      } catch (error) {
        return {
          isError: true as const,
          content: [{ type: 'text' as const, text: formatError(error) }],
        };
      }
    };
  }

• src/tools/describe-all-tables.ts:11-19 (schema)

  Input schema and description for the describe_all_tables tool. Accepts an optional 'database' string parameter.

  export const describeAllTablesToolConfig = {
    title: 'Describe All Tables',
    description:
      'Show the schema of all tables at once. Much more efficient than calling describe_table for each table individually. ' +
      'Warning: response can be large for databases with many tables — prefer describe_table for specific tables when possible.',
    inputSchema: {
      database: z.string().optional().describe('Database name. Uses the current database if omitted.'),
    },
  };

• src/tools/index.ts:41-46 (registration)

  Registration of describe_all_tables with the MCP server, including its name, description, input schema, and handler.

  server.tool(
    describeAllTablesToolName,
    describeAllTablesToolConfig.description,
    describeAllTablesToolConfig.inputSchema,
    createDescribeAllTablesHandler(runner),
  );

• src/tools/index.ts:8-12 (registration)

  Import of describeAllTablesToolName, describeAllTablesToolConfig, and createDescribeAllTablesHandler from the module.

  import {
    describeAllTablesToolName,
    describeAllTablesToolConfig,
    createDescribeAllTablesHandler,
  } from './describe-all-tables.js';

• src/tools/format-column.ts:1-22 (helper)

  The formatColumn helper used by describe_all_tables to format each column's output string (name, type, constraints, defaults, etc.).

  export interface ColumnInfo {
    name: string;
    type: string;
    nullable: boolean;
    key: string;
    defaultValue: unknown;
    extra: string;
    comment: string;
  }
  
  export function formatColumn(col: ColumnInfo): string {
    let result = `${col.name} ${col.type}`;
    if (!col.nullable) result += ' NOT NULL';
    if (col.key === 'PRI') result += ' PK';
    else if (col.key === 'UNI') result += ' UNIQUE';
    else if (col.key === 'MUL') result += ' INDEX';
    if (col.defaultValue != null) result += ` DEFAULT ${col.defaultValue}`;
    if (col.extra) result += ` ${col.extra}`;
    if (col.comment) result += ` -- ${col.comment}`;
    return result;
  }