Decoding without the key
A Caesar cipher has only 25 possible shifts, so you can break it by trying them all. This tool does that for you. It shows the text decoded with each shift, and scores every result by how closely its letters match normal English.
How the scoring works
In English, some letters are far more common than others: E, T and A appear often, while Z and Q are rare. A correct decoding has letter counts that look like English, and a wrong one does not. The tool measures the difference with a standard chi-squared score. The lower the score, the better the fit, and the bar shows each result compared with the best one.
Reading the table
- Look for the row marked Most likely, and read its preview.
- Press Show to display the full decoded text for any shift.
- Shift 0 is your original text, which is useful for checking whether it was encrypted at all.
Short texts and other languages
Scoring needs enough letters. With fewer than about 20 letters, the best-scoring shift may not be the right one, so read the previews yourself. The scoring is tuned for English. For another language, trust your own reading of the table.
If nothing looks right
The text may use a different cipher, such as a keyword-based Vigenere cipher or a general substitution cipher, or it may include extra scrambling. A Caesar cipher always keeps word lengths and spacing, so spaces that look wrong are a clue.
If you do know the shift, use the Caesar cipher tool. To make your own puzzle, try the generator. For the theory behind breaking it, read the guide.