Caesar Cipher Decoder & Encoder
Encode and decode Caesar shift, ROT13, ROT47 and Atbash text, or brute-force all 25 shifts at once. Everything runs in your browser.
The Caesar Cipher Decoder runs entirely in your browser. The plaintext and ciphertext you type or paste stay on your device and are never uploaded to ArrayKit.
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About Caesar Cipher / ROT13
The Caesar Cipher Decoder encodes and decodes the classic shift cipher and its well-known cousins — ROT13, ROT47 and Atbash — from one panel. Pick Caesar and choose any shift from 1 to 25 to encode a message or turn it back to plaintext; the shift and Encode/Decode toggle do the arithmetic for you. ROT13, ROT47 and Atbash are keyless and self-inverse, so a single click transforms and untransforms them. When you have ciphertext but not the key, the Brute-force panel lists all 25 Caesar rotations side by side so you can eyeball the readable one instantly. Case and every space, digit and punctuation mark are preserved. It is built for CTF players, puzzle hunters, students and anyone learning cryptography — and it runs entirely on your device, so the text you paste is never uploaded.
Features
- Caesar mode with any shift from 1 to 25 and an Encode/Decode toggle
- ROT13 for letters and ROT47 for all printable ASCII, each self-inverse
- Atbash mirror cipher (A↔Z) that needs no key
- Brute-force panel showing all 25 Caesar shifts at once for cracking
- Copy any single brute-force line or the whole transformed result
- Preserves letter case and passes digits, spaces and punctuation through
- Live output that updates as you type or adjust the shift
- Runs entirely in your browser — pasted text is never uploaded
How to use the Caesar Cipher / ROT13
- Choose a cipher: Caesar, ROT13, ROT47, Atbash or Brute-force
- For Caesar, set the shift (1–25) and pick Encode or Decode
- Type or paste your text into the input pane
- Read the transformed result on the right and copy it
- Unsure of the key? Open Brute-force and pick the readable line
Example
Input
Attack at dawn
Output
Dwwdfn dw gdzq
A Caesar shift of 3 moves each letter three places forward; decode by shifting 3 back.
Common errors & troubleshooting
- Decoded Caesar text is still gibberish. — You likely used the wrong shift. Try the Brute-force panel to see all 25 rotations and pick the one that reads as plain language.
- ROT13 does not scramble digits or symbols. — ROT13 only rotates A–Z letters by design. Use ROT47 instead, which rotates digits and punctuation along with letters.
- ROT47 mangled a whole sentence including spaces. — ROT47 leaves spaces alone but rotates every other printable character. Run ROT47 a second time to recover the original text.
- Accented or non-Latin letters came through unchanged. — These ciphers operate on the ASCII A–Z alphabet only, so characters like é, ñ or Cyrillic pass through untouched.
Frequently asked questions
- How do I decode a Caesar cipher without knowing the shift?
- Switch to the Brute-force panel and paste the ciphertext. It lists all 25 possible Caesar rotations at once, so you can scan them and copy the line that reads as normal words — no guessing one shift at a time.
- Why is ROT13 the same for encoding and decoding?
- ROT13 is a Caesar shift of 13, and the alphabet has 26 letters. Shifting by 13 twice moves a letter a full 26 places, back to where it started, so applying ROT13 again perfectly reverses it.
- What is the difference between ROT13 and ROT47?
- ROT13 only rotates the 26 letters A–Z and leaves digits and punctuation alone. ROT47 rotates 94 printable ASCII characters — letters, digits and symbols — by 47, so it scrambles far more of the text while staying self-inverse.
- How does the Atbash cipher work?
- Atbash mirrors the alphabet: A becomes Z, B becomes Y, and so on down to Z becoming A. It has no numeric key and is its own inverse, so encoding and decoding are the same operation.
- Is a Caesar cipher secure enough to protect real data?
- No. Caesar, ROT13, ROT47 and Atbash are historical or obfuscation ciphers with at most 25 keys, trivially broken by brute force. Use them for puzzles, CTFs and learning — never for real secrets. For that, use hashing or proper encryption.
- Does the tool keep the original letter case and punctuation?
- Yes. Uppercase stays uppercase and lowercase stays lowercase, and every space, digit and punctuation mark passes through unchanged, so the shape of your message is preserved after encoding or decoding.
Related tools
All ArrayKit tools