ctrl_

Press a key, {{name}}, and watch the Control key strip it down to the byte it really sends. ASCII, 1967, still wired to your keyboard.

decoder

Ctrl-I

the I key

& 0x1F — the Control key clears the top two bits. That is the whole mechanism.

^I HT Horizontal Tab 0x09 · 9

click here, then press any key

works with Tab, Enter, Escape, Backspace too — the real control keys. click anywhere else to release.

the 32 control characters · 0x00–0x1F

Click any cell, or just press its letter on your keyboard. Red cells have a dedicated key on a modern keyboard — and your terminal cannot tell the two apart.

the one that breaks the pattern

DEL 0x7F · 127 · the last position in the table

DEL is alone at the far end because of paper tape. A teletype punched characters as patterns of holes — a hole is a 1, and you can punch a hole but never un-punch one. To delete a character already committed to the tape, you backed up one column and punched out every remaining hole, turning it into all-bits-set. Readers were told to ignore that value. DEL is 0x7F because 0x7F is the one value you can always reach.

ASCII (ASA X3.4-1963, then X3.4-1967) placed every control character exactly 0x40 below a printable one, so a single bitwise AND could convert between them. On a Teletype Model 33 the Control key did this in hardware — it held two bits low while the rest of the keyboard closed. Sixty years later your keyboard still works the same way: that is why Ctrl-C is ETX, why Ctrl-[ is Escape, and why Tab and Ctrl-I are, byte for byte, the same keystroke.

ANSI escape sequences · what ESC opens up

parse a sequence

type or paste a sequence — \e, ESC, or ^[ all work as the escape prefix