ROT13 / Caesar Cipher
Encode or decode text with ROT13 or any Caesar shift (1–25). Useful for spoiler protection and puzzles.
Quick answer: ROT13 / Caesar Cipher: encode or decode text with ROT13 or any Caesar shift (1–25). Useful for spoiler protection and puzzles. Runs entirely in your browser, free, no signup.
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A Caesar cipher shifts every letter by a fixed amount, and ROT13 is simply the special case of a 13-place shift. Because 13 is exactly half of the 26-letter alphabet, applying ROT13 twice returns the original text — the operation is its own inverse. That self-reversing property is why forums and newsgroups adopted it decades ago to hide spoilers, punchlines, and answer keys in plain sight.
It is worth stating plainly that this is obfuscation, not encryption. A Caesar cipher has only 25 possible keys, so anyone can break it by trying each shift or by frequency analysis in seconds. Treat it as a puzzle toy or a courtesy veil, never as protection for anything sensitive. For real confidentiality use the AES-256-backed secure note encryptor instead.
The tool leaves digits, spaces, and punctuation untouched and preserves letter case, which is exactly what capture-the-flag challenges and classic word puzzles expect. If you know the message was shifted but not by how much, decode with each shift from 1 to 25 and scan for the reading that turns gibberish into English.
Frequently asked questions
- Is this real encryption?
- No — the Caesar cipher was broken about 2,000 years ago. Use it for puzzles, hiding spoilers in forum posts, and CTF challenges. For real privacy, use our Secure Note Encrypt/Decrypt tool, which uses AES-256.
- Why is ROT13 useful?
- ROT13 is its own inverse — encoding twice returns the original. It's the conventional way to hide plot spoilers, joke punchlines and mild profanity in plaintext forums and email.
- Does it preserve case?
- Yes — uppercase letters map to uppercase, lowercase to lowercase. Non-letters are passed through unchanged.
- Can I shift by negative amounts?
- There's no need — a left shift of 3 is the same as a right shift of 23. Use whichever direction matches the puzzle you're solving.
- Is my text uploaded?
- No — the substitution runs entirely in your browser.