Why this tool is useful
Use the keyed Polybius square to inspect coordinate substitution and the explicit I/J merge required by a 25-cell Latin alphabet.
Text & List Tools · runs locally
Keyed Polybius Square Cipher Tool
Build a deterministic 5×5 keyed Polybius square, encode Latin text to coordinates or decode validated coordinate groups.
Ready. Your working data stays in this browser.
How it works
A deduplicated optional keyword fills the square before A–Z; J shares I, coordinates use row then column digits 1–5 and slash marks a word boundary.
Practical example
With an empty keyword, HELLO WORLD becomes 23 15 31 31 34 / 52 34 42 31 14 and decodes to the same normalized phrase.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.