Caesar Cipher Translator

This Caesar cipher translator won't ask you for a number. Most folks landing here don't have one, just a scrap of gibberish from a puzzle or a kid's note. All 25 shifts drop into the box, and coded text gets a bet on top. Paste Khoor Zruog. First line: Hello World.

What Is the Caesar Cipher?

It's a swap. Every letter slides the same distance down the alphabet. Caesar himself used three, if you trust Suetonius. Augustus, with an empire to run, went with one. Not exactly a tough upgrade, was it?

How Does the Caesar Cipher Work?

Pick a number. Slide. At 3, A is D. X falls off the end and lands on A. Math teachers write it as position plus shift, mod 26, with the letters numbered 0 to 25. Digits don't move. Neither do spaces.

Shift	A becomes	hello becomes	Known as
1	B	ifmmp	The one Augustus used
2	C	jgnnq	Just a number
3	D	khoor	Caesar's own
4	E	lipps	Just a number
5	F	mjqqt	Just a number
6	G	nkrru	Just a number
7	H	olssv	Just a number
13	N	uryyb	ROT13
23	X	ebiil	Undoes shift 3
25	Z	gdkkn	Undoes shift 1

How Do You Decode a Caesar Cipher Without the Key?

Try them all. Twenty-five keys is nothing, and a bored kid with a pencil gets there before lunch. Picking the winner took me more work. Common English words count first. No match? Letter frequency. English loves e and t and barely touches z. Al-Kindi, working in 9th-century Baghdad, got there first. I just typed it up.

Coded line I tried	Top line in the box
Dwwdfn dw gdzq	Attack at dawn
Wkh txlfn eurzq ira	The quick brown fox
Uryyb	Hello
Khoor Zruog	Hello World
Pmttw	Hello

When Won't It Find the Answer?

Short text. My early version swore xyz was rst, all because those are common letters. So I made it earn the top line: one real English word, or 15 letters at least. No proof, no guess. A name might land blank, and then it's you and the list. Short words can fool it too. That's why the other 24 lines stay on screen, right where your own eyes can overrule my code, and they'll do that better than any scorer I could write this year.

English only, too. Feed it French and the scorer's lost, even with the right answer sitting on line 9. Mixed alphabet? Shift that changes per letter? Different cipher, and all 25 lines will be junk.

Encoding a Message

Typed plain text? Take any line. Tell a friend the number, or don't. They can paste it here too. Reversing a known key means 26 minus the shift, so shift 3 gets undone by line 23.

Why There's No Key Box

Plenty of Caesar pages have a slider, and I skipped it on purpose, because a slider only helps when you already know the number and most people searching for this are staring at a note they can't read. Twenty-five lines can feel like a lot on a phone, I'll grant you, so the guess on top saves the scrolling once the text is long enough to score. It also lets a kid with a homework sheet check every answer on one screen, without pressing a single button after the paste.

Fair warning for teachers, then. A whole class can paste your worksheet in here in about four seconds, so a Caesar homework sheet mostly tests honesty, which may still be worth testing on a slow Friday afternoon.

Is It Safe for Real Secrets?

No. Escape rooms are the sweet spot, where a clue costs a ten-year-old five minutes with a paper strip and costs nobody anything if it leaks. A birthday treasure hunt works the same way, as long as nobody at the party has a phone and a suspicious older brother who knows what ROT13 means. ROT13 got popular on old Usenet groups for hiding spoilers, which is about the right level of secrecy. Passwords? Please don't, since anyone with this page and a spare ten seconds can read the lot, and that includes the kid who sits behind you in class.

More codes? Dots and dashes live at the Morse Code Translator, ones and zeros at the Binary Translator. Nerd out on the Caesar cipher article on Wikipedia, or browse the translators page.

Caesar Cipher Questions, Answered

How do you decode a Caesar cipher? Paste it in. Top line reads like English? Done. Otherwise it's a minute of scanning all 25 lines, tops.

What is the key in a Caesar cipher? A number. It's between 1 and 25, and that's the whole lock, so don't hide anything good behind it.

Can it decode with a key I already know? Sure. Take 26 minus your key and read that line. Key of 3? Shift 23.

What is ROT13? Caesar at 13. Run it twice and you're back at the start, since 13 is half of 26, so old Usenet folks never needed a second tool.

Does a Caesar cipher change numbers? Not here. Only A to Z move. Some puzzles shift digits too, and those will need your pencil.

Who used the Caesar cipher? Julius Caesar, for his military letters. Augustus after him. Bernardo Provenzano, a Sicilian mafia boss, was still writing notes in a variation until 2006, and police breaking them helped catch him. Bad plan.