Two-way translation
Type a message to see its tap code. Or paste tap code to read it back as text. One click swaps the direction.
Tap Code Translator
Translate text to tap code and back, with audio knock playback and a visual grid.
Tap Code Translator
Tap code turns letters into pairs of knocks. No radio, no light, no tools — just sound. It was used by prisoners of war to talk to each other through prison walls, when any other form of communication was too risky. This page explains how it works and lets you try it yourself.
Where tap code comes from
Tap code has old roots. A version of it dates back to 19th-century Russian prisons, where inmates tapped messages through cell walls. It became widely known through American prisoners of war held in North Vietnam during the Vietnam War. Isolated in separate cells, they used it to share news, keep morale up, and organize resistance — all without saying a word out loud.
The code survived because it needs almost nothing to work. You don't need to see the other person. You don't need a device. You just need something to tap on, and a shared understanding of the grid below.
How the code works
The 26 letters go into a 5×5 grid. That's only 25 spots, so two letters share one: C and K. Most versions use K's spot for both, since the two letters sound similar anyway.
A
B
K/C
D
E
F
G
H
I
J
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Each letter has a row number and a column number, both from 1 to 5. To send a letter, you tap the row number, pause, then tap the column number. The letter N sits in row 3, column 3 — so you'd tap three times, pause, then tap three more times.
A short pause separates the two numbers. A longer pause separates one letter from the next. That's the whole system — no memorizing rhythms, no special equipment, just counting.
What this tool does
Audio playback
Hear the actual knock pattern, not just read it. Useful for practicing recognition by ear, the way it's really used.
Live grid highlight
While the audio plays, the matching cell lights up on the 5×5 grid. You see the row light up first, then the exact letter, in sync with the knocks.
Adjustable speed
Slow it down while you're learning the grid. Speed it up once you can recognize rows and columns without thinking.
Tips for learning it
- Learn the grid, not a lookup table. Once you know where each letter sits, you can work out the tap pattern on the spot. You don't need to memorize 26 separate codes.
- Practice counting, not tapping speed. The hard part isn't tapping fast. It's counting taps accurately while listening, especially past three or four in a row.
- The pause matters more than the taps. A clear gap between the row count and the column count is what makes the message readable. Rushed, uneven pauses cause more confusion than slow tapping ever does.
- Expect to lose C and K. Since they share a spot, decoding "1-3" could mean either letter. Real users rely on context to tell them apart — the same way you'd guess a misspelled word from the sentence around it.
Frequently asked questions
What is tap code?
Tap code is a way to send letters using only knocking sounds. Each letter is represented by two numbers — a row and a column in a 5×5 grid — sent as two groups of taps.
Why do C and K share the same code?
Because 26 letters don't fit evenly into a 5×5 grid of 25 spots. C and K were combined since they sound alike, so mixing them up rarely changes the meaning of a message.
Who used tap code, and why?
It's best known from American prisoners of war held in North Vietnam, who used it to talk through solid cell walls without being seen or heard clearly by guards. Earlier versions were used in Russian prisons in the 1800s.
Is tap code the same as Morse code?
No. Morse code uses short and long signals (dots and dashes) of different lengths for each letter. Tap code uses only one kind of signal — a knock — and tells letters apart by how many knocks and in what grouping, not by signal length.