A combining character, not HTML or Markdown#
Normal strikethrough — the <s> tag in HTML, or ~~text~~ in Markdown — is formatting applied on top of plain text, and it disappears the instant it lands somewhere that does not render that markup, showing raw tildes or tags instead. This tool works differently: it inserts a Unicode "combining long stroke overlay" character directly after every letter. That mark is part of the text itself, not a formatting instruction, so it survives being pasted into a plain-text field with zero rendering support for HTML or Markdown — an Instagram bio, most chat apps, a plain comment box.
Why this is more reliable than the box-drawing lookalike tricks#
Some other stylized-text tricks (upside-down text, for instance) work by substituting each letter with an unrelated character that merely looks similar — an approximation. Strikethrough here is not an approximation: it is a genuine combining mark stacked on the original, unmodified letter, so the letter itself renders correctly and the line is added on top of it, the same way an accent mark stacks on a letter like é.
Where the line might look thin or slightly offset#
Combining marks are positioned by the font rendering the text, and different fonts handle vertical alignment of combining characters with slightly different precision — the strike can look perfectly centered in one app and marginally high or low in another. This is a font-rendering quirk shared by every tool using this technique, not something specific to how this one generates the text.