# Tap Code > Translate text to tap code and back: the 5×5 knock code American prisoners of war tapped through cell walls, with the full chart and how to tap it. - Page: https://linguaholic.com/tools/tap-code/ - Type: free online tool (Converters & translators), no sign-up, runs in the browser - Publisher: Linguaholic (https://linguaholic.com/), made by Marcel Iseli - Last updated: October 3, 2026 - Open it pre-filled: https://linguaholic.com/tools/tap-code/?text=hello - `text`: text to encode, or tap groups (dots, letters separated by /) to decode (for example `hello`) - `mode`: direction: encode (default) or decode (for example `decode`) - `open`: open a section: steps (the tap-code grid and worked letters), frequency (letter counts) or identify (which cipher is this?) (for example `steps`) ## What is tap code? **Tap code** is a way to spell out words with nothing but knocks. The letters sit in a 5×5 grid. To send a letter you tap its row number, pause, then tap its column number: two taps and then three taps mean row 2, column 3, which is H. Because the grid has only 25 cells, the letter K is dropped and tapped as C. It is also called the **knock code**, and it is famous as the code American prisoners of war tapped through the walls of their cells in Vietnam. All you need is something to tap on and the ability to count to five, which is exactly why it worked there. ## How to use the tap code translator 1. Choose **Encode** to turn text into taps, or **Decode** to turn taps back into text. 2. When encoding, each letter appears as two groups of dots: the row and then the column. HELLO is `.. ... / . ..... / ... . / ... . / ... ....`. 3. To decode, paste dot groups in the same layout: a space between the two groups of a letter and a slash between letters. 4. Tap **Copy** to save the result. The grid view in the tool shows which row and column each letter comes from. Since K becomes C, a decoded message may show C where you expect K: KICK comes back as CICC. Real tap code readers fix that from context, and so should you. ## Frequently asked questions **What is tap code?** Tap code spells out letters with knocks using a 5×5 grid. You tap the row number, pause, then tap the column number, so two taps and then three taps mean H. **How does tap code work?** The letters A to Z, without K, fill a 5×5 grid in order. Each letter is sent as two groups of taps: the first for its row and the second for its column, with a longer pause between letters. **Why is there no K in tap code?** Twenty-six letters do not fit in 25 cells, so K is dropped and tapped as C, which often makes the same sound. Readers fix it from context. **How do you learn the tap code alphabet?** Remember the first letter of each row, A, F, L, Q and V, and count the rest in alphabetical order, skipping K. That is the whole grid. **How do you decode tap code?** Count each group of taps and write the numbers down in pairs, then look each pair up in the grid: row first, column second. In the tool, choose Decode and paste dot groups with a slash between letters. **Who used tap code?** It is best known from American prisoners of war in Vietnam, who began spreading it in Hanoi's Hoa Lo prison in June 1965. Prisoners in tsarist Russia are said to have used a similar knock code. **Is tap code the same as Morse code?** No. Morse code uses short and long signals with a different pattern for each letter. Tap code needs only one kind of tap and the grid, so it is slower but much easier to learn and to hear through a wall. **How do you send numbers in tap code?** The grid has no digits, so numbers are spelled out as words, such as TWO instead of 2. **Is this tap code translator free and private?** Yes. It runs entirely in your browser with no sign-up, and nothing you type is uploaded or stored. ## Data sources The code breaker's English letter frequencies and word checks come from Linguaholic’s English dictionary, built from the open ENABLE and SCOWL word lists. 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