Caesar Cipher Encoder & Decoder
Shift letters by any amount from 1 to 25 to encrypt or decrypt text, or brute force every shift at once.
When this is off the output is written entirely in capitals, the way classical cipher texts are usually presented.
How to Use the Caesar Cipher Encoder & Decoder
- Type or paste your message into the input box. Letters A–Z and a–z are shifted; spaces, digits, and punctuation stay exactly where they are.
- Choose the shift with the number field or drag the slider — both stay in sync, so you can jump straight to a known key or sweep through values by hand.
- Click "Encrypt" to apply the shift, or "Decrypt" to reverse it. Decrypting simply applies the opposite shift, so the same key works in both directions.
- If you do not know the key, click "Brute force: try all 25 shifts" and read down the list until one line turns into real words.
- Copy the whole result with "Copy result", copy a single brute-force row with its own copy button, or press "Clear" to start over.
What Is the Caesar Cipher?
The Caesar cipher is the oldest substitution cipher still in common use as a teaching example. Named after Julius Caesar, who reportedly used it for military dispatches, it replaces each letter with one a fixed number of places further along the alphabet. With a shift of 3, A becomes D and Z wraps around to C. The shift is the entire key, which means there are only 25 useful keys in the Latin alphabet, and decrypting is just shifting in the opposite direction.
This is a classical cipher with no real security, and it must never be used to protect secrets. Twenty-five keys can be tried by hand in under a minute — that is exactly what the brute force button on this page does — and even without brute force, English letter frequencies give the shift away almost immediately. Treat the Caesar cipher as a puzzle, a classroom demonstration, or a CTF warm-up, never as protection for passwords, personal information, or anything confidential.
When the shift is fixed at 13 the cipher becomes the familiar ROT13 encoder and decoder, which is its own inverse. If your data genuinely needs to stay private, use the AES encrypt and decrypt tool instead, and when you only need text that survives URLs, JSON, or email, reach for the Base64 encoder and decoder.
Frequently Asked Questions (FAQ)
How do I decrypt a Caesar cipher without the key?
Use the "Brute force: try all 25 shifts" button. It prints every possible decryption at once, and because there are only 25 keys you simply scan the list for the row that reads as normal language.
What shift does the Caesar cipher normally use?
Historical accounts describe Caesar using a shift of three, which is why 3 is the default here. Any value from 1 to 25 works equally well, and a shift of 13 gives you ROT13.
How do you decrypt a Caesar cipher by hand?
Subtract the shift from each letter instead of adding it, wrapping past A back to Z. That is identical to encrypting with 26 minus the shift, which is exactly what this tool does when you press Decrypt.
Does the Caesar cipher change numbers and punctuation?
No. This tool shifts only the 26 basic Latin letters. Digits, spaces, line breaks, punctuation, and accented characters pass through untouched so the message keeps its original shape.
Is the Caesar cipher secure enough for real data?
Not at all. With only 25 possible keys it falls to brute force instantly, and letter-frequency analysis breaks it even faster on longer texts. Use modern encryption for anything that actually matters.
What is the difference between the Caesar cipher and ROT13?
ROT13 is one specific Caesar cipher with the shift locked to 13. Because 13 is half of 26, encrypting and decrypting are the same operation, which is not true for other shifts.
What does "preserve letter case" do?
Leave it on and uppercase stays uppercase while lowercase stays lowercase. Turn it off and the whole output is capitalised, matching how cipher texts are traditionally written in puzzles and textbooks.
Is my message uploaded anywhere?
No. Every shift, decryption, and brute-force row is computed in your browser with JavaScript. ToolGenie never sees, stores, or transmits the text you enter.
Tips for Cracking and Using Caesar Ciphers
- Tip 1: Look for one-letter words in the brute-force list first. In English they are almost always "a" or "I", which pins the shift down in seconds.
- Tip 2: Remember that encrypting with shift N and decrypting with shift 26 minus N give the same result, so a shift of 20 and a shift of -6 are the same key.
- Tip 3: Paste only a sentence or two into the brute-force view. Short samples make the 25 candidates far easier to scan than a full page of text.
- Tip 4: Fix the shift at 13 and you have the ROT13 translator; switch to AES encryption the moment the content is genuinely sensitive, and use the Base64 converter when you only need transport-safe text.