Caesar Cipher / ROT13
Encode or decode text with a Caesar shift cipher. ROT13 preset and brute-force decoder included.
Educational use only. Caesar ciphers can be brute-forced in milliseconds (literally: that’s what the third tab does). For real protection use the Encrypt & Decrypt tool with AES-256.
About Caesar Cipher / ROT13.
Caesar Cipher and ROT13 Encoder / Decoder
The Caesar cipher is the simplest substitution cipher in cryptographic history — every letter is shifted forward by a fixed amount in the alphabet. ROT13 is the special case where the shift is exactly 13 (the same operation encodes and decodes). CipherForces Caesar Cipher tool encodes, decodes, and brute-forces shift ciphers entirely in your browser.
Three Modes
- Encode: Pick a shift (1–25, default 13 for ROT13) and the plaintext is shifted forward. Punctuation, numbers, and spaces are preserved.
- Decode: Same operation in reverse — given the ciphertext and the shift used, recover the plaintext.
- Brute-force: Don't know the shift? The tool prints all 25 possible decryptions in one column so you can eyeball which one reads as English. Useful for puzzle hunts and CTF challenges.
What Caesar Is — and Isn't — Good For
This is a classroom and puzzle-hunt cipher, not real cryptography. Twenty-five possible shifts are trivially brute-forced in a fraction of a second; even a frequency-analysis attack on a single sentence usually reveals the shift instantly. Do not use Caesar (or ROT13) to protect anything that matters. For real encryption use our Encrypt & Decrypt tool (AES-256).
Common Use Cases
- Puzzle hunts and ARGs: Caesar shifts are a common first-layer cipher. Brute-force mode solves them in one click.
- Spoiler text on forums and Reddit: ROT13 is the convention — readers who want to see the spoiler decode it deliberately.
- Teaching cryptography basics: The clearest possible illustration of substitution and why key space matters.
- Light obfuscation in code: Hide an easter-egg string in source so it doesn't grep cleanly.
Privacy
Pure JavaScript string transformation. Nothing leaves your browser. The "secret" of a Caesar cipher is the shift number, which is also trivial to discover — but at least our tool isn't logging your text either way.
Frequently asked questions.
How do I decode a Caesar cipher when I don't know the shift?
Paste your text and run the brute-force decoder. It generates all 25 possible shifts at once, so you can scan the list and spot the readable English line. No need to guess the key first, and you can copy the correct result with one click.
Is my text uploaded to a server when I use this Caesar cipher tool?
No. The tool runs entirely in your browser using JavaScript, so your text never leaves your device or touches a server. There is no signup and nothing is stored. You can disconnect from the internet after the page loads and it still encodes and decodes.
What is ROT13 and how is it related to the Caesar cipher?
ROT13 is a Caesar cipher with a fixed shift of 13. Because the alphabet has 26 letters, applying ROT13 twice returns the original text, making encoding and decoding the same operation. This tool includes a one-click ROT13 preset alongside custom shift values.
Can I use this tool to both encode and decode shift cipher messages?
Yes. Choose any shift from 1 to 25 to encode plain text, or set the matching shift to decode a message back to readable form. You can also use the ROT13 preset or the brute-force option when the original shift is unknown.
How to use Caesar Cipher / ROT13.
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