Polybius square encode
Polybius square encode, classical cipher, a puzzle not a protection, computed on your device. Not reversible to the exact input: only letters survive (J folds into I) and case, spacing and punctuation are dropped.
Polybius square encode looks up each letter on a 5 by 5 grid keyed by key, blank by default, and prints its row and column as a two-digit pair. J is folded into I before the lookup, so the two letters produce the same pair. Only the 25 letters have a position, so case, spacing, digits and punctuation are all dropped.
Questions
What is the default key?
A blank string, which builds the plain unkeyed alphabet in order, A through Z with J merged into I.
What does the output look like?
Space-separated two-digit pairs, one per letter, each digit being a row or column number from 1 to 5.
What happens to J?
It is folded into I first, so both letters produce the same pair.
What is dropped?
Everything but the 25 letters: case, spacing, digits and punctuation all disappear, since only letters have a grid position.
Is this a real cipher?
It carries no key beyond the grid arrangement itself, so it is a puzzle format rather than real protection.
Can I use this from the command line?
Yes, the same code runs on the page, the CLI and MCP.