ROT13 Decoder

ROT13 Decoder

Paste the scrambled text into Text, and with Decode selected it’s turned back into plain text as you type. ROT13 is the default. If you know the text used a different shift, choose ROT-N and set the Shift from 1 to 25. For text where digits or punctuation were scrambled too, choose ROT18 or ROT47.

If you don’t know the shift, the Try every shift panel lists all 25 readings. The readable one gives it away, and one click applies it. Accented letters, other alphabets, spaces and punctuation pass through unchanged.

Use the result as input, Copy, Example and Clear work as you’d expect, and everything runs in your browser.

Example

A geocache hint, written in ROT13 so you only read it if you want to:

Haqre gur ebpx arne gur oevqtr

decodes to: Under the rock near the bridge.

Is it ROT13? How to recognise it

ROT13 text keeps its shape: the same word lengths, the same spaces and punctuation, capitals in the same places. Only the letters change, and the most common English words always turn into the same letter groups. If you see these, it’s ROT13:

A text full of gur and naq is almost certainly ROT13, and the default setting decodes it straight away.

The other variants look different:

• ROT18 looks just like ROT13, but the numbers are wrong too. “Zrrg ng 7571” is “Meet at 2026”.
• ROT47 doesn’t look like words at all. It’s a mix of letters, digits and symbols such as =, @ and [, with only the spaces kept. “w6==@[ (@C=5P” is “Hello, World!”.

When you don’t know the shift

A Caesar cipher can use any shift from 1 to 25. Rather than guessing, open Try every shift. Each line is your text shifted back by that line’s number, so the readable line’s number is the shift. Take:

Dwwdfn dw gdzq, wkh hqhpb vohhsv

Line 3 reads “Attack at dawn, the enemy sleeps”: the message was shifted by 3, the shift Julius Caesar is said to have used. Click Use on that line to take it as your result.

Finding the shift by hand

You can also work it out from the letters themselves. In English text, E is the most common letter. Count the letters in the scrambled text: whichever appears most often is probably E, and the distance from E to it is the shift.

• In Dwwdfn dw gdzq, wkh hqhpb vohhsv, the most common letter is h. E to H is 3, so the shift is 3.
• In a longer ROT13 text, such as Zrrg zr ng gur byq zvyy nsgre qnex naq oevat gur xrl, the most common letter is r. E to R is 13.

This works best on a sentence or more. In a few words, other letters can easily outnumber E.

When no shift makes sense

If none of the 25 lines reads as words, the text wasn’t made with a single shift. Some likely alternatives:

• Atbash swaps A with Z, B with Y and so on. “the” becomes gsv, so look for that.
• Vigenère uses a keyword, so the shift changes from letter to letter. Look for repeated groups of letters.
• A substitution cipher maps every letter to an unrelated one. It keeps word shapes like ROT13 does, but no shift of the alphabet will fix it.
• Not a cipher at all. A long mix of upper case, lower case and digits, often ending in =, is Base64. Groups of 0s and 1s are binary. Text full of %20 and %3A is URL encoding.

What stays the same

Only the plain Latin alphabet A to Z is shifted, plus the digits in ROT18. Accented letters such as é and ñ, other scripts such as Cyrillic or Chinese, emoji, spaces, line breaks and punctuation pass through exactly as they are. ROT47 also shifts digits and punctuation, but only plain ASCII ones.

FAQ

Is decoding ROT13 different from encoding it?

No. ROT13 shifts letters by 13, halfway round the alphabet, so the same step encodes and decodes. The same goes for ROT18 and ROT47. Only ROT-N with another shift needs the direction set correctly. To hide text instead, use the ROT13 Encoder.

Why is my decoded text still unreadable?

Probably the wrong variant. Text with scrambled numbers needs ROT18, text full of symbols needs ROT47, and text that isn’t ROT13 at all needs Try every shift. If no line reads, see “When no shift makes sense” above.

Can ROT13 protect a message?

No. It only keeps text from being read by accident: anyone who sees gur knows what they’re looking at, and any Caesar shift falls to 25 tries. For anything private, use real encryption.