HTML Outline is a free Chrome add-on developed by Rectus Inc. It is a handy tool that allows users to easily view the outline of an HTML page.

With HTML Outline, users can quickly identify the types of tags that are being used as headings or sectioning elements. This is particularly useful for web developers and designers who want to ensure proper structure and organization of their HTML documents.

Additionally, if a heading tag contains only an image, HTML Outline will display the alt attribute of the image. This feature helps users understand the content of the image even when it is not visible.

Overall, HTML Outline is a valuable tool for anyone working with HTML pages. It provides a clear and visual representation of the page structure, making it easier to navigate and understand the content.