Cipher & Code Tool

Cipher Tool turns a message into a classic secret code and back again. Type in “Plain text” and the coded version appears beside it; paste a coded message into “Coded text” and it is decoded the other way. Ten ciphers are built in: Caesar with any shift, ROT13, ROT47, Atbash, Vigenère with a keyword, Affine, rail fence, A1Z26 numbers, Bacon’s A/B code and plain reversed text.

It is made for puzzle hunts, escape rooms, geocaching, classroom lessons on the history of codes and anyone who has found a strange line of letters and wants to know what it says. Capital letters, spaces and punctuation stay where they were, so “Attack at dawn!” comes back looking like a sentence rather than a block of capitals.

If you have a Caesar message but no idea of the shift, the tool tries all 25 and ranks them by how closely each answer matches the letter patterns and common words of English, so the real message is usually at the top. It does the same for all 311 Affine keys. Nothing you type leaves your device.

1. Under “Cipher”, pick one of the ten, such as Caesar or Vigenère.
2. Set its key if it has one: the Shift, the Keyword, a and b for Affine, or the number of Rails.
3. Type in “Plain text” to encode, or paste into “Coded text” to decode. The other box fills in as you type.
4. For a Caesar or Affine message with an unknown key, look at the “Try all” table and press “Use” on the row that reads as English.
5. Press “Copy” above either box. “Swap” moves the result across so you can run it through again.

• Ten ciphers: Caesar, ROT13, ROT47, Atbash, Vigenère, Affine, rail fence, A1Z26, Bacon and reverse (whole text, each word or word order).
• Works both ways at once, with two linked boxes and a Swap button.
• Keeps capitals, spaces, digits and punctuation in place for the letter ciphers.
• Caesar code-breaker: all 25 shifts ranked by an English letter-frequency score plus common-word check, with a “Use” button on each row.
• Affine code-breaker that tries all 311 working keys and shows the best 12.
• A letter strip that shows exactly which letter becomes which for Caesar, ROT13, Atbash and Affine.
• Any Caesar shift, including negatives and numbers over 25, with a note on what it equals.
• Bacon’s cipher in the modern 26-letter form or Bacon’s own 24-letter alphabet, where I and J, and U and V, share a code.

• The ranking needs a little text to work with. From about 12 letters the right Caesar shift is nearly always first; with only a word or two, check a few rows.
• In Vigenère the keyword only moves on when it meets a letter, so spaces and commas don’t throw the key out of step. Some puzzle sites count every character instead; if a decode looks half right, that is usually why.
• ROT13, ROT47 and Atbash undo themselves: put the coded text in either box and you get the answer.
• A1Z26 and Bacon can’t carry capital letters, so decoded text comes back in capitals. Numbers already in your message are read as letters when decoding A1Z26.
• Rail fence moves every character, including spaces. If a puzzle removed the spaces before encoding, remove them before decoding too.