What ⇆ means
It marks action in both directions.
Nearby labels decide whether it means a swap, feedback, or flow; without them, read it as “back and forth.”
A 1737 French engineering treatise used arrows to show water flow and a waterwheel's rotation, an early example of arrows in technical diagrams.
Technical and diagrammatic; unlabeled, it reads as “back and forth.”
Label both sides when direction matters; ⇆ does not say what moves.
Don't confuse it with
4↹⇄⇋⇌
Leftwards Arrow To Bar Over Rightwards Arrow To Bar
shares “arrow”, “leftwards”, “over”, “rightwards”
Rightwards Arrow Over Leftwards Arrow
shares “arrow”, “leftwards”, “over”, “rightwards”
Leftwards Harpoon Over Rightwards Harpoon
shares “leftwards”, “over”, “rightwards”
Rightwards Harpoon Over Leftwards Harpoon
shares “leftwards”, “over”, “rightwards”
Questions people ask
1Why does ⇆ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ⇆
Windows (Word)
Alt+XType 21C6, then Alt+X to get ⇆.
Windows
Win+Rrun charmap for the full table, or use the emoji picker's Ω symbols tab (Win + .).
macOS
Control+Command+SpaceOpen the character viewer and search “leftwards arrow over rightwards arrow”.
Linux
Ctrl+Shift+UType 21c6, then Enter or Space.
HTML
⇆CSS
\21C6HTML
HTML entity `⇆` represents ⇆.
MathML
MathML entities include `lrarr` and `leftrightarrows`.
Codes and encoding1 code points
HTML decimal
⇆
HTML hex
⇆
CSS content
content: "\21C6";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%87%86
1
On screen
1
Code points
1
JS .length
3
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.