> For the complete documentation index, see [llms.txt](https://huy312100.gitbook.io/software-development/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://huy312100.gitbook.io/software-development/system-design/fundamental/design-a-web-crawler/step-3-design-deep-dive/url-frontier.md).

# URL frontier