Caesar Cipher Decoder
Try all 25 shifts
What is Caesar Cipher Decoder
This decoder reverses the Caesar cipher: give it the shifted text and the key, and it returns the original message. If you do not know the key, the 'Try all 25 shifts' panel shows every possible decoding at once, so you can spot the readable one by eye. Only letters are shifted; numbers, spaces, and punctuation stay put. Everything runs locally in your browser.
How to use
- Paste the Caesar cipher text you want to read.
- Set the shift slider to the key that was used to encode it.
- Read the decoded message in the output box.
- Do not know the key? Open 'Try all 25 shifts' and scan the list for the line that makes sense.
When to use it
Handed a scrambled line like 'Khoor, Zruog!' and no key? Open the brute-force panel and shift 3 reveals 'Hello, World!'. This is the tool for CTF challenges, puzzle hunts, and old ROT13 messages where the shift is unknown. If you already know the key, just set the slider and read it straight off.
Frequently asked questions
How do I decode without knowing the shift?
Open 'Try all 25 shifts'. It lists the text decoded with every key from 1 to 25, so the one line that reads as normal language is your answer.
What if only some letters look right?
The Caesar cipher uses a single shift for the whole message, so the correct key makes the entire text readable at once. If only part looks right, the message may use a different cipher, such as Vigenère.
Does decoding happen on a server?
No. The text is decoded in your browser and never uploaded. Nothing you paste is sent or stored.
Can I share this with my text and shift pre-filled?
Yes. The URL updates automatically as you type. Copy it from the address bar or use the Copy link button, and anyone who opens it sees your exact text and shift ready to go.
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