Microsoft Word's built-in checker is a tool designed to help users improve their writing. It automatically checks for spelling and grammar errors as you type, highlighting mistakes and suggesting corrections. This feature makes it easier to create polished documents without needing extensive proofreading. In addition to spelling and grammar, the checker also offers style suggestions to enhance clarity and readability. Users can customize the settings to focus on specific writing issues, making it a versatile tool for both casual and professional writing tasks.