Caesar encode
Caesar encode. A classical cipher, computed on your device.
Runs on your device. The file is never uploaded.
Caesar encode moves every letter in your text forward by the shift you set, 3 by default, wrapping z round to a and leaving everything else alone. Fractions and any shift outside 1 to 25 are turned away. Twenty-five keys exist in total, so Caesar brute force reads the message back without holding one.
Questions
Does this protect anything?
No. A Caesar cipher has 25 possible keys and is broken by trying all of them, which the Caesar brute force tool on this site does in one run. It is a puzzle and a teaching example, nothing more. Do not use it for anything you need kept private; use AES-GCM encrypt for that.
What does shift do?
It moves each letter forward through the alphabet by that many places, wrapping from z back to a. The default is 3, the classic value. Only whole numbers from 1 to 25 are allowed, and anything else is refused with "shift must be a whole number between 1 and 25". A shift of 13 gives the same result as the ROT13 tool.
What happens to numbers, spaces and punctuation?
They are left exactly as they are. Only A to Z and a to z are shifted, and case is preserved, so an uppercase letter stays uppercase. Word lengths, spacing and punctuation all survive the encoding, which is one of the reasons the cipher is so easy to break by eye.
How do I get my text back?
Use Caesar decode with the same shift. It applies the negative of the number you enter, so encode with 3 and decode with 3. Encoding again with 23 also works, since the two shifts add up to 26, but the decode tool is the one meant for the job.
How do I give it my text?
As a file. Drop a text file and the contents are read as UTF-8 text; drop several and each is transformed separately, using the same shift for all of them in that run. Accented and non-Latin letters pass through untouched, because only the 26 English letters are in the mapping, so text in Greek or Cyrillic comes out exactly as it went in.
Does my text get uploaded?
No. The transformation is a few lines of string manipulation running in a Web Worker in this tab. Nothing is sent, nothing is stored, and the site works offline. That does not make the cipher secure; it only means the plaintext stays on your machine.