Crack any Caesar cipher in seconds. Encode with a custom shift, decode with a known one, or brute-force all 25 shifts and let the tool rank the most likely plaintext — with one-click ROT13.

Caesar Cipher Decoder — Encode, Decode & Brute Force Online

Caesar Cipher Decoder

Encode secret messages with any shift from 1 to 25, decode messages when you know the shift — or hit Brute Force and test all 25 shifts at once, automatically ranked so the correct plaintext lands on top. Free, instant, and 100% private.

Plain text to encode

Shift Shift 3

Cipher text

Cipher text to decode

Known shift Shift 3

Decoded with known shift

Brute-force results — best match first

Rank	Shift	Decoded text	English hits

Ranked by how many common English words each candidate contains. For very short or non-English messages, eyeball the full list — the right answer is in there.

100% private

Everything runs in your browser’s JavaScript. Your messages are never sent anywhere.

No signup

No accounts, no email, no limits. Encode and decode as much as you want.

Free forever

A learning and puzzle tool that stays free, with no premium tier hiding features.

How to use the Caesar Cipher Decoder

1Encode a message
Stay on the Encode tab, type your message, pick a shift with the slider (or hit the ROT13 quick button for shift 13), and press Encode. Copy the cipher text to share it.
2Decode with a known shift
On the Decode tab, paste the coded message, set the shift it was encoded with, and press “Decode with known shift” for an instant answer.
3Brute force an unknown shift
No idea what shift was used? Press “Brute force all 25 shifts” — the tool tries every shift and ranks the results by English-word matches, so the real message usually lands at rank 1.

Why use this Caesar cipher tool

True brute force, ranked

All 25 possible shifts are tested in milliseconds and scored against a built-in dictionary of 100 common English words — the correct decryption bubbles to the top automatically.

Encode and decode in one place

Write secret notes for friends, solve puzzle-hunt clues, or check your own homework — both directions of the cipher live in one tabbed tool.

One-click ROT13

ROT13 (shift 13) is the classic internet spoiler-tag cipher. One button sets it up — handy for forums, puzzle games, and casual obfuscation.

Case and punctuation preserved

Uppercase stays uppercase, lowercase stays lowercase, and numbers, spaces, and punctuation pass through untouched — only A–Z letters shift.

Copy buttons everywhere

Copy the encoded output, the known-shift decode, or any single brute-force row with one tap — no manual text selection on mobile.

Great for classrooms and CTFs

Teachers can demo substitution ciphers live, and capture-the-flag players can crack Caesar-encoded flags in seconds instead of by hand.

Caesar Cipher FAQs

What is a Caesar cipher?

It is one of the oldest known ciphers, named after Julius Caesar. Each letter in your message is shifted forward by a fixed number of positions in the alphabet — with shift 3, A becomes D, B becomes E, and so on, wrapping around after Z.

How does the brute-force decoder work?

There are only 25 possible shifts, so the tool simply tries all of them and decodes your message 25 ways. Each candidate is scored by counting how many common English words it contains (the, and, you, hello, and 96 more). The highest score is almost always the real message.

What is ROT13?

ROT13 is a Caesar cipher with shift 13. Because the alphabet has 26 letters, applying ROT13 twice returns the original text — so the same button both encodes and decodes. It is traditionally used to hide spoilers and puzzle answers.

Will brute force work on very short messages?

Sometimes the ranking needs a few words to be confident — a 3-letter message can score ties across shifts. For short texts, scan the full ranked table yourself; the correct reading is still in the list, it just may not be rank 1.

Does it work with languages other than English?

The encode/decode shifts work for any text using the A–Z alphabet, but the brute-force ranking dictionary is English, so it scores non-English messages poorly. For other languages, decode with the known shift instead.

Is the Caesar cipher secure?

No — it is a learning toy, not real security. With only 25 possible keys it falls to brute force instantly (which is exactly what this tool demonstrates). For real privacy, use modern encryption like AES — see our AES text encryptor linked below.

Are my messages sent to a server?

Never. The shifting, brute force, and ranking all run in JavaScript inside your browser tab. Nothing you type leaves your device.

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