Caesar Cipher Encoder / Decoder
Type or paste text, pick a shift from 1 to 25, and see the encoded and decoded results update live.
Encoded text appears here
Decoded text appears here
Brute-force all 25 shifts
Enter some text above to see it decoded at every shift.
Letters keep their case; numbers, spaces, and punctuation pass through unchanged. Everything runs in your browser.
How it works
- Type or paste your text into the box — letters keep their case and everything else passes through unchanged.
- Move the shift slider (1–25) or press ROT13 to set a shift of 13; the encoded and decoded outputs update as you type.
- Copy the result you need, or open the brute-force panel to see your text decoded at every possible shift.
Frequently asked questions
- How does a Caesar cipher work?
- Each letter is replaced by the letter a fixed number of positions further along the alphabet, wrapping from Z back to A. With a shift of 3, A becomes D and Y becomes B. Decoding simply shifts in the opposite direction by the same amount.
- How do I crack a Caesar cipher without knowing the shift?
- Because there are only 25 possible shifts, you can try them all. Open the brute-force panel below the outputs and scan the 25 candidate decodings — the readable one reveals both the message and the shift used.
- What is ROT13 and why does it have its own button?
- ROT13 is a Caesar cipher with a shift of exactly 13, half the 26-letter alphabet. That makes it self-inverse: applying ROT13 twice returns the original text, so the same operation both encodes and decodes. It is commonly used to hide spoilers and puzzle answers.
- Does this tool handle numbers, punctuation, and mixed case?
- Uppercase and lowercase letters are shifted while keeping their case, so “Hello” stays capitalized after encoding. Digits, spaces, punctuation, and any non-Latin characters pass through untouched, which matches how the classical cipher is defined.
- Is my text uploaded anywhere when I use this tool?
- No. All encoding, decoding, and brute-forcing run entirely in your browser with plain JavaScript — nothing is sent to a server or stored. You can even load the page, disconnect from the internet, and keep working.
About this tool
This tool encodes and decodes text with the Caesar cipher, one of the oldest known encryption methods, named after Julius Caesar, who reportedly used a shift of 3 for military correspondence. You choose a shift between 1 and 25, and every letter in your text is rotated that many positions through the alphabet. Both directions are shown at once: the encode output shifts letters forward, and the decode output shifts them backward, so you never have to think about which way a message was transformed.
Everything happens locally in your browser. As you type or move the slider, the tool maps each character code arithmetically — uppercase letters rotate within A–Z, lowercase within a–z, and every other character is left exactly as it is. No text ever leaves your device, so you can safely paste puzzle fragments, homework exercises, or anything else without it touching a server.
The brute-force panel is the fastest way to crack an unknown message. Since a Caesar cipher has only 25 usable keys, the panel lists your input decoded at every shift from 1 to 25. Skim the list until one line reads as normal language; that line is the plaintext and its number is the key. This is also a good hands-on demonstration of why such small key spaces are considered trivially breakable in modern cryptography.
A few practical tips: use the ROT13 button when you want a reversible obfuscation for spoilers or quiz answers, since shifting by 13 twice restores the original. If you are checking a geocaching hint or CTF challenge, paste the whole ciphertext rather than a fragment — longer text makes the correct brute-force row much easier to spot. And remember this cipher is for learning and puzzles only; it offers no real security for sensitive data.