A slug is the human-readable part of a URL that identifies a page, the trailing segment of something like example.com/blog/my-first-post. Turning a title into one means lowercasing it, replacing spaces with hyphens, and removing anything that does not belong in a URL.
Getting this right matters for a few reasons that compound. A clean slug is readable in search results and in a shared link, which affects whether people click. It survives being pasted into chat, email and documents without being mangled by percent-encoding. And it is stable: a slug derived from a title is something you can keep even if you later reword the heading.
The part that is easy to get wrong is non-ASCII text. Accented characters, non-Latin scripts and emoji are all technically permitted in a modern URL, but they get percent-encoded the moment the link travels anywhere, turning a tidy address into an unreadable run of escape sequences. This tool transliterates accented Latin characters to their closest ASCII equivalent, so a title with é or ü produces a slug with e and u, and strips characters it cannot sensibly transliterate rather than leaving them to be escaped.
It also handles the small details that make a slug look deliberate: collapsing runs of separators into one hyphen, trimming hyphens from the ends, removing stray punctuation and quotes, and optionally dropping common English stop words to keep a long headline's slug short. Every line is converted independently, so you can paste a list of titles and get a list of slugs back.