Is a Caesar cipher secure?

No. There are only 25 possible keys, so trying every one takes minutes by hand. It is a puzzle and a teaching tool, not encryption.

A Caesar cipher with a shift of 13. Because 13 is half of 26, applying it twice returns the original text.

How do you break one without the key?

Try all 25 shifts and read down until a line becomes English. The solving aids on this page show exactly that.

Does it handle punctuation and capitals?

Yes — case is preserved and anything that is not a letter passes through unchanged.

Caesar Cipher Generator

Shifts every letter of your message a fixed number of places through the alphabet, producing a puzzle to hand out. The answer is one tap away, there is a hint for anyone stuck, and the solving aids show all 25 possible shifts — which is the point of the lesson, because 25 is a very small number.

Your message

Anything you type stays in your browser — it is never uploaded, and never put in the page address.

Letter groups

0 keeps the words. 5 sets it in classic five-letter blocks.

Seed (optional)

A word that makes the same puzzle come back — useful for a worksheet.

Choose the shift myself rather than drawing one at random

Remove the spaces between words (much harder)

Your puzzle will appear here.

What this generator does

Produces a puzzle with a guaranteed answer, which is what makes it usable in a classroom: the reveal is the exact text you typed, so a pupil who does the work correctly gets the right answer. Unlike the cryptogram generator next to it, the Caesar shift has only 25 possible keys, which makes it the one to teach first and the one that demonstrates why key space matters.

How to use this tool

Type your message.
Let the tool pick a shift, or choose one yourself.
Optionally remove the spaces or set the letters in blocks to make it harder.
Press Make puzzle, then print it or reveal the answer.

Understanding the controls

Your message: Only A–Z letters move. Spaces, punctuation, digits and accented characters pass through untouched, which keeps the word shapes visible and the puzzle solvable.
Shift: How many places each letter moves forward, wrapping from Z back to A. A shift of 13 is ROT13, which is its own inverse — encoding twice returns the original.
Letter groups: Zero keeps the words as written. Five sets the text in classic five-letter blocks, which hides word lengths and makes the puzzle considerably harder.
Remove the spaces: Takes away the biggest clue a solver has. Word shapes are how most people crack a short cipher, so removing them changes the difficulty sharply.
Seed: Brings the same puzzle back, which matters for a worksheet — you can regenerate the identical sheet next term rather than a different one.

Worked examples

A shift of 3: HELLO becomes KHOOR — the shift Julius Caesar is said to have used.
A shift of 13: ROT13. Encoding twice gets you back to where you started, so the same button both hides and reveals.
Wrapping: XYZ with a shift of 3 becomes ABC, because the alphabet loops.

Common use cases

A computing or maths lesson introducing ciphers and key spaces
A history lesson on classical cryptography
A treasure hunt or escape-room clue
A puzzle page for a school newsletter
A code-breaking club activity with a worked solution

How this generator works

Each letter is converted to its position in the alphabet, moved forward by the shift, wrapped round at 26 and converted back, with case preserved. Decoding shifts the same distance backwards, so the two operations are exact inverses. Anything outside A–Z is copied straight through, which is why punctuation and accents survive intact.

Randomness and fairness

The only random choice is the shift, drawn from 1 to 25 — a shift of 0 is excluded because it would leave the message unchanged. Choosing the shift yourself makes the puzzle fully determined, and a seed makes a random shift reproducible so a worksheet can be regenerated exactly; a seeded shift comes from a deterministic, non-cryptographic generator, which is entirely appropriate here because nothing about this tool is secure in the first place.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

This is a puzzle, not encryption. With 25 possible keys, anyone can try all of them in a couple of minutes — the solving aids on this page do exactly that, which is the teaching point rather than an oversight.
Only the 26 letters A–Z are shifted. Accented letters, other alphabets and emoji pass through unchanged, which can leak information about the message.
Word shapes and spacing give a great deal away in a short message. Turn spacing off, or use letter groups, if you want a real challenge.
The message is limited to 2,000 characters, which is plenty for a puzzle and not intended for long documents.

Common mistakes

Treating a Caesar cipher as a way to hide something real: It has 25 keys and is broken by trying all of them. Use it for puzzles and lessons only — never for anything that matters.
Leaving a one-letter word in the message: A single letter is almost certainly A or I, which gives a solver the shift immediately. Reword, or turn spacing off.
Revealing the answer before printing: The reveal is on screen only and resets whenever you make a new puzzle, but check it is hidden before showing the page to a class.

Practical tips

Set a shift yourself when preparing several sheets, so you know the key without having to reveal each one.
Show the 25-shift list after pupils have solved one by hand — the contrast between fifteen minutes of work and a glance down a list is the lesson.
Use a message with no one-letter words for a genuinely harder puzzle.

Privacy and your data

Your message is encoded in your browser and never sent anywhere. It is not stored between visits and never written into the page address, so a link you share carries the tool and not your text. Analytics records the puzzle's length and never its content. Because nothing here is secure, do not use it for anything you actually need to keep private.

A recreational and educational puzzle tool. Classical ciphers like this one offer no security whatever and must never be used to protect real information.

Frequently asked questions

Is a Caesar cipher secure?: No. There are only 25 possible keys, so trying every one takes minutes by hand. It is a puzzle and a teaching tool, not encryption.
What is ROT13?: A Caesar cipher with a shift of 13. Because 13 is half of 26, applying it twice returns the original text.
How do you break one without the key?: Try all 25 shifts and read down until a line becomes English. The solving aids on this page show exactly that.
Does it handle punctuation and capitals?: Yes — case is preserved and anything that is not a letter passes through unchanged.