Simple Caesar cipher to encrypt or decrypt text instantly
ROT13 encoder decoder tool converts text to ROT13 cipher and decodes ROT13 back to readable text instantly. Simple Caesar cipher that rotates letters by 13 positions in the alphabet. Perfect for light obfuscation, puzzles, and learning cryptography basics.
ROT13 (“rotate by 13 places”) is a simple letter substitution cipher that replaces a letter with the 13th letter after it in the alphabet. It’s a special case of the Caesar cipher which was used by Julius Caesar to protect military messages.
A → N, B → O, C → P, …, M → Z, N → A, O → B, …, Z → M. ROT13 is its own inverse: applying ROT13 twice returns original text.
ROT13(ROT13(text)) = text. Same function encodes and decodes, making it perfect for simple obfuscation without separate encryption/decryption keys.
Spoiler hiding in forums, puzzle creation, simple message obscuring, teaching cryptography basics, and light text protection.
The ROT13 algorithm operates on the basic Latin alphabet of 26 letters:
For uppercase letters (A-Z, ASCII 65-90):
ROT13(char) = {
if (char between 'A' and 'M'): char + 13
if (char between 'N' and 'Z'): char - 13
else: keep unchanged
}
For lowercase letters (a-z, ASCII 97-122):
ROT13(char) = {
if (char between 'a' and 'm'): char + 13
if (char between 'n' and 'z'): char - 13
else: keep unchanged
}
| Original | ROT13 | Type | Description |
|---|---|---|---|
| HELLO | URYYB | Uppercase | Basic word |
| world | jbeyq | Lowercase | Basic word |
| Hello World | Uryyb Jbeyq | Mixed case | Common phrase |
| 12345 | 12345 | Numbers | Unaffected by ROT13 |
| !@#$% | !@#$% | Symbols | Unaffected by ROT13 |
A ↔ N G ↔ T M ↔ Z S ↔ F Y ↔ L B ↔ O H ↔ U N ↔ A T ↔ G Z ↔ M C ↔ P I ↔ V O ↔ B U ↔ H D ↔ Q J ↔ W P ↔ C V ↔ I E ↔ R K ↔ X Q ↔ D W ↔ J F ↔ S L ↔ Y R ↔ E X ↔ K
a ↔ n g ↔ t m ↔ z s ↔ f y ↔ l b ↔ o h ↔ u n ↔ a t ↔ g z ↔ m c ↔ p i ↔ v o ↔ b u ↔ h d ↔ q j ↔ w p ↔ c v ↔ i e ↔ r k ↔ x q ↔ d w ↔ j f ↔ s l ↔ y r ↔ e x ↔ k
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Hide spoilers in online discussions. Readers must decode ROT13 to reveal content, preventing accidental spoilers.
Create simple cryptography puzzles, escape room clues, and educational games teaching basic encryption concepts.
Teach students about substitution ciphers, modular arithmetic, and basic cryptography principles in computer science classes.
The ROT13 cipher has its roots in ancient cryptography. Julius Caesar used a shift cipher (now called Caesar cipher) with a shift of 3 to protect military messages. ROT13 emerged in the early internet era as a convenient variation:
| Cipher | Shift | Scope | Description |
|---|---|---|---|
| ROT13 | 13 | A-Z, a-z | Standard self-inverse cipher |
| ROT5 | 5 | 0-9 | Numbers only, 0↔5, 1↔6, etc. |
| ROT47 | 47 | ASCII 33-126 | All printable ASCII characters |
| Caesar Cipher | 1-25 | A-Z, a-z | Any shift value (1-25) |
| Atbash Cipher | – | A-Z, a-z | A↔Z, B↔Y, C↔X, etc. |
No, ROT13 is not secure for real encryption. It provides only basic obfuscation and can be broken instantly by anyone who knows the algorithm. ROT13 is useful for hiding text from casual viewers (like spoilers) but offers no real security against determined attackers.
ROT13 is its own inverse because applying it twice returns the original text: ROT13(ROT13(text)) = text. This happens because the alphabet has 26 letters, and rotating by 13 twice equals rotating by 26, which brings you back to the starting position (26 ≡ 0 mod 26).
Standard ROT13 only affects letters (A-Z, a-z). Numbers (0-9), punctuation, spaces, and special characters remain unchanged. However, variants like ROT47 extend the cipher to include numbers and printable ASCII characters.
Several languages have ROT13 support: PHP has str_rot13(), Python has codecs.encode(text, 'rot13'), Perl has tr/A-Za-z/N-ZA-Mn-za-m/, and many Unix systems have rot13 command. Most languages can implement ROT13 with simple string manipulation.
ROT13 is a substitution cipher that only affects letters, leaving other characters unchanged. Base64 is an encoding scheme that converts binary data to ASCII text using 64 characters. Base64 is for data representation, while ROT13 is for simple text obfuscation. Base64 encoded text appears random, while ROT13 text looks like normal text but unreadable.
Real-time ROT13 encoding/decoding with no delays
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Our ROT13 encoder decoder tool provides everything you need for simple text obfuscation. Encode text to ROT13, decode ROT13 back to readable text, and explore the fascinating world of basic cryptography.