A trailing slash is a forward slash (“/”) placed at the end of a URL such as domain.com/ or domain.com/page/. The trailing slash is generally used to distinguish a directory which has the trailing slash from a file that does not have the trailing slash. However, these are guidelines and not requirements.
In the past, a folder would have a trailing slash and a file would be without the trailing slash. A folder would indicate there were more files and you’d typically have an index file (index.html, index.php, etc.) where the content of the page would load from. So the content would come from say domain.com/page/index.html but domain.com/page/ would be shown to users. With individual files, you’d have the file name and no trailing slash on the end.
These days, URLs in most systems aren’t pointing to files. The URL is a record stored in a database. Serverless systems don’t even host files on your server.
Different URL structures may be treated differently. Whether you choose to use a trailing slash or not is more of a personal preference than anything. Let’s look at some common scenarios.
Trailing slashes after the domain name don’t matter
These URLs are treated exactly the same and it doesn’t matter which version you use.
Trailing slashes matter for other URLs
For every case besides the trailing slash directly after the root domain, a trailing slash will be treated as a separate URL.