Tap code is a way of encoding letters as taps using a 5x5 Polybius square. Each letter is sent as two short bursts of taps: the first counts the row and the second counts the column.

Why are there only 25 cells for 26 letters?

The 5x5 grid holds 25 letters, so C and K share the same cell. When decoding, readers infer from context whether a C or K was meant.

How do I read the dots?

Count the dots in the first group to find the row (1 to 5), then count the dots in the second group for the column. Row 4, column 4 is the 19th cell, which is T.

Where was tap code famously used?

American prisoners of war in Vietnam used tap code to communicate between cells by knocking on walls, because it needs no equipment and is easy to learn and overhear-resistant.

Is my text uploaded anywhere?

No. The entire conversion happens locally in your browser and nothing is sent to any server.

Tap Code Dot Visualiser

The tap code (also called the knock code) is a simple way to send letters as taps or knocks, made famous by American prisoners of war who used it to communicate through cell walls. Instead of showing the usual number pairs, this tool draws each letter as two clusters of dots so you can see exactly how many times to tap. Everything runs locally in your browser.

How it works

Tap code lays the alphabet into a 5×5 grid, dropping one letter so it fits 25 cells. The conventional grid omits a dedicated K and reuses the C cell for both:

   1 2 3 4 5
1  A B C D E
2  F G H I J
3  L M N O P
4  Q R S T U
5  V W X Y Z

To encode a letter you find its row and column. For example H sits at row 2, column 3, so it is tapped as tap tap … tap tap tap — a group of 2 dots, a pause, then a group of 3 dots. This tool renders the first count and the second count as separate dot groups so the rhythm is obvious at a glance.

Tips and example

The word WATER becomes:

W → row 5, col 2
A → row 1, col 1
T → row 4, col 4
E → row 1, col 5
R → row 4, col 2

Because K is not in the grid, type C instead and let the reader infer the intended letter from context. Spaces and punctuation are shown as gaps so you can keep word boundaries when tapping a longer message.