ROT13 Encoder and Decoder

How to use it

1. Pick a variant: ROT13 for letters only, or ROT47 for letters, digits and symbols.
2. Type or paste your text into the box. The sample is "Why did the chicken cross the road?".
3. Read the result below the box. It updates as you type, and there is no separate decode button.
4. To decode, paste the rotated text in and read the output. Press Copy result to take it with you.

What ROT13 does

ROT13 stands for "rotate by 13 places". Every letter moves 13 steps forward in the alphabet, and letters near the end wrap around to the start. A becomes N, B becomes O, N becomes A. Case is preserved. Digits, spaces and punctuation are not touched.

It is a Caesar cipher with one fixed shift. That shift is special: the alphabet has 26 letters, and 13 is half of 26. Shift twice and you land back where you started.

The ROT13 table

The other half is the same table read in reverse: N-Z maps back to A-M.

ROT13 decoder: why one step does both jobs

Most ciphers need a separate decoder. ROT13 does not, because it is its own inverse. Number the letters A=0 to Z=25 and the rule is (x + 13) mod 26. Apply it twice and you get (x + 26) mod 26, which is x.

So when you search for a ROT13 decoder, the encoder is the answer. Paste the rotated text into the tool above and the output is the plain text.

Worked example: "Hello"

1. H is position 7. 7 + 13 = 20, which is U.
2. e is position 4. 4 + 13 = 17, which is r.
3. l is position 11. 11 + 13 = 24, which is y. Both l letters give y.
4. o is position 14. 14 + 13 = 27. That is past 25, so subtract 26 and you get 1, which is b.

The result is Uryyb. Run it again: U (20) + 13 = 33, minus 26 is 7, which is H. You are back at Hello.

Common words in ROT13

Note that "ROT13" itself becomes "EBG13". The digits stay put.

ROT47: rotating digits and symbols too

ROT13 only handles letters. ROT47 takes the 94 printable ASCII characters, from "!" (code 33) to "~" (code 126), and rotates them by 47 places. Letters, digits and punctuation all change. 47 is half of 94, so ROT47 is also its own inverse.

The tool's second option runs this. Here is "Hello" in ROT47, step by step:

1. H has code 72. 72 - 33 = 39, plus 47 = 86. 86 is below 94, so no wrap. 86 + 33 = 119, which is w.
2. e has code 101. 101 - 33 = 68, plus 47 = 115. Subtract 94 for the wrap to get 21. 21 + 33 = 54, which is 6.
3. l has code 108. 108 - 33 = 75, plus 47 = 122, wrap to 28. 28 + 33 = 61, which is =.
4. o has code 111. 111 - 33 = 78, plus 47 = 125, wrap to 31. 31 + 33 = 64, which is @.

The result is w6==@. The default sample sentence in the tool, "Why did the chicken cross the road?", gives Jul qvq gur puvpxra pebff gur ebnq? in ROT13.

ROT47 spaces are left alone, since a space (code 32) is outside the 33-126 range.

ROT13 on the command line

On Unix and Linux you can do it without a website. The tr command maps one character set to another:

tr 'A-Za-z' 'N-ZA-Mn-za-m'

That maps A-Z to N-ZA-M and a-z to n-za-m. Feed text to it and you get ROT13 back. It is the same table as the one above.

Is ROT13 secure? Limits and mistakes

No. There is no key, the mapping is public, and letter frequencies are preserved, so frequency analysis breaks it. Even worse, a shift this common is the first thing anyone tries. It is meant to keep a spoiler from being read by accident, not to keep a secret from a person who wants it.

Real software has been caught using it for passwords. In December 1999 it was found that Netscape Communicator used ROT13 as part of an insecure scheme to store email passwords. If you need to hide data, use real encryption, not a letter swap.

Other things to watch for:

• Accented letters. "é" is not in A-Z, so it stays unchanged.
• Mixing variants. Text rotated with ROT47 will not decode with ROT13, and the reverse. Pick the same variant for both directions.
• Expecting Atbash. Atbash reverses the alphabet instead of shifting it, so Hello becomes Svool, not Uryyb.

Where ROT13 came from

ROT13 jokes were popular on newsgroup servers such as net.jokes as early as the 1980s. Posters used it to hide offensive jokes, puzzle answers and spoilers. Readers had to choose to decode it, which was the whole point.

The underlying idea is the Caesar cipher, a plain letter shift. ROT13 is the one shift that reverses itself.

Related tools

For a variable shift with brute-force help, use the Caesar cipher tool. For a cipher with a keyword, try Vigenere. If your puzzle text looks like letters and equals signs, it may be Base64 instead.

Sources

• ROT13 (Wikipedia): Usenet use, ROT5, ROT18 and ROT47, tr example, Netscape finding.
• ASCII (Wikipedia): printable character codes 33 to 126 used by ROT47.

Checked October 2026.