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Free Online Caesar Cipher and ROT13 Encoder and Decoder

Encode and decode a Caesar cipher in your browser with any shift from one to twenty five, or use the ready made ROT13, ROT5, ROT18 and ROT47. When you do not know the shift, the page lists all twenty five possibilities at once so the readable one can be picked out by eye in a second.

Free Forever Nothing Uploaded Any shift All 25 at once

Free Online Caesar Cipher and ROT13 Encoder and Decoder

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Caesar Cipher and ROT13 Everything happens in this tab. Nothing you paste is sent anywhere.

Your message

0 characters 0 words 0 lines

Shifted

0 characters 0 lines

Method

The shift 3

Also shift Digits, by the same amount within 0 to 9 Turn accented letters into plain ones first Put the result in capitals

Not sure of the shift Show me all twenty five shifts The readable one is almost always obvious at a glance.

0 letters shifted 0 digits shifted 0 left untouched - shift used

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How to Encode and Decode a Caesar Cipher

A few steps, and nothing is uploaded.

Paste the message Plain text to encode, or a shifted message to decode. A .txt file can be dropped onto the box.

Choose the method ROT13 needs nothing else set. For a Caesar cipher, drag the slider to the shift you want.

If you do not know the shift, show all twenty five The table lists every possibility. One of them will be readable English and the rest will be nonsense.

Copy the result The copy button takes the shifted text. The chain button sends the result back to the left box, which is handy for shifting twice.

What to Know About the Caesar Cipher

Why it is not security, and why ROT13 needs no decoder.

This is not security and was not secure even when it was new. There are only twenty five possible shifts, so anybody can try all of them in a few seconds, which is exactly what the table on this page does. Use it for puzzles, teaching and hiding spoilers, never for anything that matters.

ROT13 needs no separate decoder, and that is the whole point of it. Thirteen is half of twenty six, so shifting forwards thirteen and shifting backwards thirteen land in the same place. Running ROT13 on ROT13 text gives you the original, which is why it became the standard way to hide a punchline or a spoiler.

Digits are not part of the alphabet, so they need their own decision. A shift of three on the letters cannot touch a digit, because there are ten digits and twenty six letters. Shifting digits within zero to nine by the same amount is what ROT5 does, and the switch here does the same for a Caesar shift.

ROT47 is a different animal. It shifts every printable character, punctuation included, across a range of ninety four, and like ROT13 it is its own reverse. It scrambles far more thoroughly but the result is unreadable gibberish rather than something that merely looks like a foreign word.

Everything that is not a letter stays exactly where it is. Spaces, punctuation and line breaks are untouched, which keeps the shape of the message. That shape is also the main weakness of the cipher, because word lengths and the pattern of short words give a great deal away.

Key Features & Capabilities

What this tool does, and what it deliberately does not.

Any shift One to twenty five on a slider, forwards to encode and backwards to decode.

All twenty five at once The table shows every possible shift together, which is how an unknown Caesar is actually cracked.

ROT presets ROT13 for letters, ROT5 for digits, ROT18 for both and ROT47 for every printable character.

Digits handled Digits can be shifted within zero to nine, because the alphabet shift cannot reach them.

Shape preserved Spaces, punctuation and line breaks stay exactly where they were, so the result stays readable.

Nothing is uploaded The shifting is arithmetic done in this tab, so nothing you paste is sent anywhere.

About the Caesar Cipher Tool

The Caesar cipher is the first cipher almost everybody meets, and it has aged into something more useful than secrecy. It is a puzzle staple, a teaching example that takes thirty seconds to explain, and in the case of ROT13 a decades old convention for hiding a spoiler in plain sight.

Its weakness is also what makes it pleasant to work with. Twenty five possible keys means an unknown shift is not a problem to be solved but a list to be read, and showing all twenty five at once turns a puzzle that would take several minutes of fiddling into something you can solve by glancing down a column.

The small details are where other tools get tiresome. Digits need their own switch because the alphabet shift cannot reach them. Accented letters need a decision, since there is no sensible shifted form of a letter with a circumflex. And punctuation must stay put, because the moment the shape of the message changes, reading the result becomes guesswork.

Frequently Asked Questions

Shifts, ROT13, digits and cracking an unknown shift.

Switch on "Show me all twenty five shifts". The table lists every possibility with the start of each result, and the readable one stands out immediately because the other twenty four are nonsense.

Because ROT13 is its own decoder. Thirteen is half of twenty six, so applying it twice returns the original text. Paste the encoded text, choose ROT13, and the readable version appears.

No. A letter shift cannot apply to digits, since there are ten of them and twenty six letters. Switch on shifting digits, or choose ROT18, which shifts letters by thirteen and digits by five.

A shift of forty seven across all ninety four printable characters, so punctuation and symbols are scrambled too. Like ROT13 it is its own reverse, and it hides text far more thoroughly, at the cost of a result that looks like pure gibberish.

No. It can be broken by anybody in seconds, with no tools beyond a pencil, and this page will do it for them. It is for puzzles, lessons and hiding spoilers, nothing more.