Caesar Cipher Converter

Encrypt or decrypt Caesar cipher text by shifting letters while preserving punctuation and case.

1.1M uses Updated · 2026-05-24 Runs locally · zero upload
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How to Use Caesar Cipher Converter

Paste the text, choose a shift from -25 to 25, and select encrypt or decrypt. Letters move through the alphabet, uppercase stays uppercase, lowercase stays lowercase, and spaces, punctuation, numbers, and symbols remain unchanged.

Formula & Theory - Caesar Cipher Converter

The cipher maps each letter to an alphabet index, shifts it, and wraps around with modulo 26:

encrypt: C = (P + shift) mod 26
decrypt: P = (C - shift + 26) mod 26

Uppercase and lowercase letters are handled in separate alphabet ranges so A stays uppercase and a stays lowercase. Adding 26 before the modulo in decryption prevents negative indexes when the shift moves before A or a. Non-letter characters are copied directly to preserve spacing and punctuation.

Use Cases for Caesar Cipher Converter

  • Puzzle writing - Create simple shifted messages for classroom or party puzzles.
  • Cryptography lessons - Demonstrate modular arithmetic on alphabet positions.
  • Debugging examples - Test whether a Caesar decoder preserves non-letter characters.

For puzzles, Caesar cipher is charming; for privacy, use modern encryption instead.

Frequently asked questions about Caesar Cipher Converter

What characters are changed?

Only A-Z and a-z letters are shifted. Numbers, spaces, punctuation, and symbols remain unchanged.

Is Caesar cipher secure?

No. It is a classical teaching cipher and can be broken easily by trying all 26 shifts.

Is my data stored?

No. All calculations happen in your browser; nothing is sent to a server.