Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Encode or decode text with a configurable-shift Caesar cipher.
Dwwdfn dw gdzqThe Caesar cipher, named for its reported use by Julius Caesar, shifts every letter a fixed number of places through the alphabet. ROT13 is simply the special case where the shift is 13. This tool supports any shift from 1-25 in either direction (encode or decode).
Enter your text, choose a shift amount, and select Encode or Decode. Decoding with the same shift you used to encode recovers the original text.
Each letter's position in the alphabet is shifted forward (encode) or backward (decode) by the chosen amount, wrapping around at the alphabet's boundary. Case is preserved; non-letter characters pass through unchanged.
"Attack at dawn" with a shift of 5 encodes to "Fyyfhp fy ifbs".
For the fixed-shift-13 special case, see the ROT13 Cipher Tool.
Suppose you receive the message "Khoor, Zruog!" and suspect it was produced with a shift of 3. Choose Decode, type 3, and paste the text. Each letter moves three places backward: K becomes H, h becomes e, o becomes l, r becomes o, so "Khoor" reads "Hello". The comma, space and exclamation mark are untouched, and the capital letters stay capital. The result is "Hello, World!". If you had instead chosen Encode with the same shift, you would push the letters further along and get a different, unreadable string.
new position = (old position + shift) mod 26 for encoding; decoding uses the negative of the shift
The shift box is a plain number field, and the tool reduces whatever you type modulo 26 before applying it. That has a few practical consequences. A shift of 29 behaves exactly like 3, because 29 minus 26 is 3. A shift of 26 or 0 returns the text unchanged. A negative shift such as -3 in Encode mode is equivalent to shifting backward by 3, which is the same result as choosing Decode with 3. It is worth keeping this in mind if you copy a shift value from a puzzle that states it as "rotate left 4": in this tool you can enter -4 in Encode mode, or 4 in Decode mode.
Only the 26 unaccented English letters, upper and lower case, are shifted. Digits, spaces, punctuation and symbols pass through exactly as typed. Accented letters such as e with an acute accent, letters from other alphabets, and emoji are also left alone, because they are not part of the A to Z range. If you are working on a puzzle in another language, expect any accented characters to remain readable in the ciphertext, which usually gives an attacker extra clues. Case is kept letter by letter, so the pattern of capitals in your original text is still visible after encoding.
The tool does not search for the shift automatically, but it makes a manual search quick. Paste the ciphertext, set Decode, and step the shift from 1 upward, reading the first few words each time. Short messages with common words such as "the" or "and" become obvious as soon as you land on the right value. A useful shortcut is to look for the most frequent letter in a long ciphertext: in English it is most often E, so if the commonest ciphertext letter is H, a shift of 3 is a strong candidate.
Teachers can ask students to encrypt a sentence, swap papers, and decode a partner's message using only a known shift, then repeat with a secret shift and compare how long it takes to break. For escape-room or scavenger-hunt designers, a Caesar-shifted clue is a gentle first puzzle because the answer can be checked instantly here before you print the clue card.
No -- with only 25 possible shifts, it can be broken instantly by trying every shift (brute force) or by frequency analysis. It has no real cryptographic value today.
A shift of 0 (or 26) leaves text completely unchanged, since it's a full or zero rotation through the alphabet.
Yes, in principle -- with only 25 possible shifts, you can try each one until the output is readable (a technique called brute-force cryptanalysis), though this tool doesn't automate that step.
The value is reduced modulo 26, so 27 acts like 1 and 52 acts like 0. Any whole number gives a valid result.
No. Only the letters A to Z and a to z are shifted. Digits, spaces and punctuation are copied through unchanged.
Switch to Decode and enter the same shift you used originally, or stay on Encode and enter the negative of that shift. Both restore the original text.
No. They are outside the basic English alphabet range, so they pass through unchanged and remain visible in the encoded output.
Reference: MDN Web Docs