describe_table

Instructions

Implementation Reference

• lib/tools/handlers/database-tools.js:76-133 (handler)

  Core handler function that constructs and executes a SQL query to retrieve detailed schema information (columns, types, nullability, primary keys) for the specified table using INFORMATION_SCHEMA views.

  async describeTable(tableName, database = null, schema = 'dbo') {
    let query;
  
    if (database) {
      query = `
        SELECT 
          c.COLUMN_NAME as column_name,
          c.DATA_TYPE as data_type,
          c.IS_NULLABLE as is_nullable,
          c.COLUMN_DEFAULT as column_default,
          c.CHARACTER_MAXIMUM_LENGTH as max_length,
          c.NUMERIC_PRECISION as precision,
          c.NUMERIC_SCALE as scale,
          CASE WHEN pk.COLUMN_NAME IS NOT NULL THEN 'YES' ELSE 'NO' END as is_primary_key
        FROM [${database}].INFORMATION_SCHEMA.COLUMNS c
        LEFT JOIN [${database}].INFORMATION_SCHEMA.TABLE_CONSTRAINTS tc 
          ON c.TABLE_NAME = tc.TABLE_NAME 
          AND c.TABLE_SCHEMA = tc.TABLE_SCHEMA 
          AND tc.CONSTRAINT_TYPE = 'PRIMARY KEY'
        LEFT JOIN [${database}].INFORMATION_SCHEMA.KEY_COLUMN_USAGE pk 
          ON c.COLUMN_NAME = pk.COLUMN_NAME 
          AND c.TABLE_NAME = pk.TABLE_NAME 
          AND c.TABLE_SCHEMA = pk.TABLE_SCHEMA 
          AND tc.CONSTRAINT_NAME = pk.CONSTRAINT_NAME
        WHERE c.TABLE_NAME = '${tableName}' 
          AND c.TABLE_SCHEMA = '${schema}'
        ORDER BY c.ORDINAL_POSITION
      `;
    } else {
      query = `
        SELECT 
          c.COLUMN_NAME as column_name,
          c.DATA_TYPE as data_type,
          c.IS_NULLABLE as is_nullable,
          c.COLUMN_DEFAULT as column_default,
          c.CHARACTER_MAXIMUM_LENGTH as max_length,
          c.NUMERIC_PRECISION as precision,
          c.NUMERIC_SCALE as scale,
          CASE WHEN pk.COLUMN_NAME IS NOT NULL THEN 'YES' ELSE 'NO' END as is_primary_key
        FROM INFORMATION_SCHEMA.COLUMNS c
        LEFT JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS tc 
          ON c.TABLE_NAME = tc.TABLE_NAME 
          AND c.TABLE_SCHEMA = tc.TABLE_SCHEMA 
          AND tc.CONSTRAINT_TYPE = 'PRIMARY KEY'
        LEFT JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE pk 
          ON c.COLUMN_NAME = pk.COLUMN_NAME 
          AND c.TABLE_NAME = pk.TABLE_NAME 
          AND c.TABLE_SCHEMA = pk.TABLE_SCHEMA 
          AND tc.CONSTRAINT_NAME = pk.CONSTRAINT_NAME
        WHERE c.TABLE_NAME = '${tableName}' 
          AND c.TABLE_SCHEMA = '${schema}'
        ORDER BY c.ORDINAL_POSITION
      `;
    }
  
    const result = await this.executeQuery(query, 'describe_table');
    return this.formatResults(result);
  }

• lib/tools/tool-registry.js:39-50 (schema)

  Tool metadata definition including name, description, and input schema for parameter validation (table_name required, database and schema optional).

    name: 'describe_table',
    description: 'Get the schema information for a specific table',
    inputSchema: {
      type: 'object',
      properties: {
        table_name: { type: 'string', description: 'Name of the table to describe' },
        database: { type: 'string', description: 'Database name (optional)' },
        schema: { type: 'string', description: 'Schema name (optional, defaults to dbo)' }
      },
      required: ['table_name']
    }
  },

• index.js:266-273 (registration)

  Tool call dispatching in the main MCP server switch statement, mapping 'describe_table' calls to the DatabaseToolsHandler.describeTable method.

  case 'describe_table':
    return {
      content: await this.databaseTools.describeTable(
        args.table_name,
        args.database,
        args.schema
      )
    };

• index.js:241-242 (registration)

  MCP server registration for listing available tools, which includes 'describe_table' via getAllTools() from tool-registry.

  this.server.setRequestHandler(ListToolsRequestSchema, async () => ({
    tools: getAllTools()