Caesar Cipher Decoder Online
A Caesar cipher decoder (or shift cipher decoder) recovers plaintext from rotated letters. When you know the shift, decryption is one subtraction. When you do not, try each of the 26 possibilities and pick readable English—our Cipher Portal and frequency lab automate that ranking.
Decode with a known shift
If the key sheet says shift 3, select Caesar on Cipher Portal, paste ciphertext, enter 3, choose Decrypt, and run. Each letter moves backward three positions. ROT13 decoding is the same operation with shift 13.
The Caesar cipher guide explains the forward map; decoding is the inverse map using identical parameters.
Caesar cipher translator without the key
Leave the key empty on decrypt with key recovery enabled (where supported) or use the Frequency Analysis Lab Caesar demo. Each trial shift produces a candidate plaintext; chi-squared or n-gram scoring favors English-like output. See the dedicated Caesar cipher cracker walkthrough for KHOOR ZRUOG → HELLO WORLD.
This is not magic—two-letter ciphertext stays ambiguous—but newspaper cryptograms and classroom messages are usually long enough for a clear winner.
Practical decoding tips
Preserve case if your source mixed upper and lower case; Cipher Portal normalizes consistently for A–Z. Strip punctuation only if the encipherer did the same.
Compare your result with worked Caesar examples before assuming a different cipher family.
- Ciphertext
- KHOOR
- Shift
- 3
- Plaintext
- HELLO
Frequently asked questions
How do I decode Caesar cipher online?
Use Cipher Portal with cipher Caesar, enter ciphertext and shift, and decrypt—or brute force 26 shifts in the frequency lab.
What is a Caesar cipher translator?
Another name for a decoder that maps shifted letters back to readable text, often trying every shift automatically.
Can I decode without the shift number?
Yes for reasonable-length English ciphertext by scoring all 26 decryptions.
Does ROT13 need a special tool?
No—select shift 13 on any Caesar decoder.
Open the Caesar cipher decoder tool with your ciphertext.