5 by 5 coordinate cipher
Tap Code
Encode ordinary letters as strict row-column pairs, or decode validated pairs with the shared C/K cell stated clearly.
01 / Workspace
Encode or decode
Encode ASCII letters with row first and column second.
The option applies only in Decode mode. A transmitted 13 cannot reveal whether the writer meant C or K.
Use ASCII A-Z in either case. Unicode whitespace separates words. Digits, punctuation, accents, non-Latin letters, and emoji are rejected.
Keyboard shortcut: Ctrl+Enter or Command+Enter runs the selected direction.
Ready to encode.
02 / Result
Result
Each letter is a two-digit row-column pair. One space separates letters, and a standalone slash separates words.
03 / Convention
How this version works
- Find the cell. The first digit gives the row and the second gives the column. Every coordinate is exactly two digits from 1 through 5.
- Use the shared cell. Both C and K encode as
13. The decoder returns C by default, or K when that explicit option is selected. - Separate words explicitly. Encoded letter pairs have one space between them. A standalone
/is the only word separator. - Keep the alphabet strict. Encoding changes lowercase ASCII to uppercase and collapses whitespace runs between words. Punctuation and unsupported characters cause an error instead of being dropped.
Known-answer example
HELLO encodes to 23 15 31 31 34. Decoding that sequence returns HELLO.
KICK encodes to 13 24 13 13. Standard decoding returns CICC because every 13 is ambiguous.
5 by 5 reference grid
Read the row label first, then the column label.
| Row / col | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| 1 | A | B | C/K | 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 |
Limits and security
- Input is limited to 5,000 Unicode code points and 10,000 UTF-16 code units. Browser text fields normalize CR and CRLF line endings to LF.
- The decoder accepts only coordinate tokens from
11through55, standalone slash tokens, and whitespace. It rejects missing digits, joined tokens, extra symbols, out-of-range digits, and misplaced slashes. - Decoded text is uppercase. The C/K choice applies to every
13; context is the only way to recover a writer's original choice. - Tap Code is a classical cipher for education and puzzles. It is unsuitable for sensitive data and provides no modern security.