How do I break a Caesar cipher without the key?

Try all twenty-five shifts — one will produce readable text. With longer messages, frequency analysis is faster: the most common letter in English text is usually E, so find the most frequent cipher letter and work out the offset.

What is the difference between this and ROT13?

ROT13 is a Caesar cipher with the shift fixed at thirteen. Because thirteen is half the alphabet, it is self-inverse — a property no other shift value has.

Can I use this for anything real?

No. Twenty-five possible keys is no security at all. For anything that genuinely needs protecting, use established encryption — a shift cipher is a puzzle, not a safeguard.

Encode & Decode

Caesar Cipher Encoder & Decoder

The Caesar cipher shifts each letter a fixed number of places through the alphabet. Named for Julius Caesar, who reportedly used a shift of three for military correspondence, it is the simplest substitution cipher there is — and ROT13 is just the special case where the shift is thirteen.

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Input

String

Alphabet Shift Key

Action Mode

Result

Ylehodqg Vlwh

About

What the Caesar Cipher Encoder & Decoder does

It offers no real security. With only twenty-five possible shifts, an attacker can simply try all of them, and letter-frequency analysis breaks it instantly on any reasonable length of text. It remains a useful teaching example and a staple of puzzles and escape rooms.

How it works

Using the Caesar Cipher Encoder & Decoder

1Enter your text.
2Choose a shift value between 1 and 25.
3Select encrypt or decrypt.
4Each letter moves that many places, wrapping around at the end of the alphabet.
5Decrypting applies the same shift in the opposite direction.

Use cases

What people use it for

Creating a puzzle or treasure hunt clue
Solving a cipher in a game or escape room
Demonstrating substitution ciphers when teaching
Lightly obscuring a spoiler

FAQ

Frequently asked questions

6 related

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