Why does ROT13 use the same tool for both encoding and decoding?

ROT13 shifts each letter 13 places through the alphabet, and the alphabet has 26 letters — so shifting by 13 twice lands back where you started. That makes ROT13 a self-inverse cipher: running the same text through it twice restores the original.

Is ROT13 actually secure?

No — it's not encryption in any meaningful sense. ROT13 is a simple substitution with no key, historically used to hide spoilers, punchlines, or offensive text from casual reading, not to protect sensitive data.

What happens to numbers and punctuation?

They're left untouched. Only letters A–Z and a–z are shifted; digits, spaces, and symbols pass through unchanged, and case is preserved.

What's the shift field for?

It generalizes ROT13 into a full Caesar cipher — any shift from 1 to 25 rotates the alphabet by that many positions. Shift 13 is the classic ROT13; other values are useful for exploring how Caesar ciphers work.

ROT13 ENCODER / DECODER

Encode or decode text with ROT13, or any Caesar shift. Nothing leaves your browser.

Shift

Input

Output (shift 13)

Gur dhvpx oebja sbk whzcf bire gur ynml qbt.

How to use ROT13

1
Type or paste your text into the input box.
2
Use the ROT13 preset, or enter a custom shift value for a general Caesar cipher.
3
Read the transformed text — apply it again with the same shift to reverse it.
4
Copy the result.

Questions

Why does ROT13 use the same tool for both encoding and decoding?: ROT13 shifts each letter 13 places through the alphabet, and the alphabet has 26 letters — so shifting by 13 twice lands back where you started. That makes ROT13 a self-inverse cipher: running the same text through it twice restores the original.
Is ROT13 actually secure?: No — it's not encryption in any meaningful sense. ROT13 is a simple substitution with no key, historically used to hide spoilers, punchlines, or offensive text from casual reading, not to protect sensitive data.
What happens to numbers and punctuation?: They're left untouched. Only letters A–Z and a–z are shifted; digits, spaces, and symbols pass through unchanged, and case is preserved.
What's the shift field for?: It generalizes ROT13 into a full Caesar cipher — any shift from 1 to 25 rotates the alphabet by that many positions. Shift 13 is the classic ROT13; other values are useful for exploring how Caesar ciphers work.