ROT13 Encoder & Decoder
Encode a short message or decode existing ROT13 text with the same operation, without changing its spacing, punctuation, line-break structure, or non-ASCII text.
A QUICK WALKTHROUGH
How to use this tool
- Maximum 100,000 UTF-16 code units. Only ASCII A–Z/a–z change; all other text and line breaks stay in place. Updates 200 ms after typing stops.
- Apply ROT13 once to rotate every ASCII letter by 13 positions.
- Review the exact result, then copy it or download a text file. Apply ROT13 again to restore the original.
One symmetric letter substitution
ROT13 maps A–M to N–Z and N–Z back to A–M, with the same rule for lowercase letters. Because the alphabet contains 26 letters, applying the transformation twice restores the exact browser text value.
A deliberately narrow character scope
Only the ASCII ranges A–Z and a–z change. Digits, punctuation, whitespace, line breaks, accented letters, other scripts, emoji, and every remaining UTF-16 code unit in the browser text value stay in their original positions. Output length therefore always equals input length.
Live conversion, swapping and counts
Typing pauses for 200 ms before conversion; the manual button remains available. Swap requires a valid result and applies ROT13 again to restore the previous input. Statistics count UTF-16 code units, rotated ASCII letters and unchanged code units, not displayed characters; a surrogate pair counts as two units. Empty or oversized input clears the old result, statistics and download. Nothing is stored.
GOOD TO KNOW
Common questions
Do I choose between encode and decode?
No. ROT13 uses the same operation in both directions. Apply it once to transform the text and a second time to restore the source.
Will accented or non-English letters change?
No. ROT13 is defined here only for the 26 ASCII English letters. Characters such as é, ñ, 中文, and emoji remain unchanged.
Is ROT13 secure encryption?
No. It is a simple, widely recognizable substitution used for obfuscation and puzzles. Anyone can reverse it immediately by applying ROT13 again.