Skip to main content
Z

Caesar Cipher — Encrypt, Decrypt & Auto-Detect Shift Cipher

Encrypt and decrypt with the classic Caesar shift cipher. Includes auto-detect using English letter frequency.

Free No signup Client-side Privacy friendly Updated

Detected shift:

How to use

  1. 1 Pick Encrypt, Decrypt, or Auto-decrypt mode.
  2. 2 For Encrypt/Decrypt, choose a shift (1–25).
  3. 3 For Auto-decrypt, the tool tries all 25 shifts and picks the one closest to English letter frequencies.
  4. 4 Copy the result.

Why use this tool

  • Configurable shift 1–25.
  • Auto-decrypt uses chi-squared scoring against English letter frequency.
  • Preserves case, digits, punctuation, whitespace.
  • Educational tool for cryptography classes.

Frequently asked questions

Is Caesar cipher secure?

No — trivially broken by frequency analysis (try our Auto-decrypt). Use only for puzzles and education, never for actual security.

How does auto-decrypt work?

It tries all 25 possible shifts and computes a chi-squared distance between the resulting letter distribution and standard English. The lowest chi-squared wins.

Why does auto-decrypt sometimes pick the wrong shift?

Auto-detect works best on English plaintext longer than 50 characters. Short inputs or non-English text can mislead the frequency analysis.

What is Caesar Cipher?

A Caesar Cipher is a tool that encrypts and decrypts text using the classic Caesar shift cipher, replacing each letter with one a fixed number of positions away in the alphabet. It runs entirely in the browser and includes an auto-detect mode that uses English letter frequency to recover the likely shift, making it useful for decoding classical ciphers without knowing the key.

Features

Encrypt & decrypt

Apply any shift 0–25; decrypting is the inverse shift.

Auto-detect shift

Frequency analysis guesses the key so you can crack a cipher without it.

100% client-side

Text is transformed locally and never uploaded.

Example

Input

Zerethon (shift 3)

Output

Chuhwkrq

Common use cases

  1. 1

    Solve puzzles & CTFs

    Decode classic shift ciphers in puzzle hunts and beginner CTF challenges.

  2. 2

    Teach cryptography basics

    Demonstrate substitution ciphers and why they fall to frequency analysis.

  3. 3

    Crack an unknown shift

    Use auto-detect to recover the key from ciphertext alone.

Summary

Zerethon's Caesar cipher shifts each letter a fixed number of positions to encrypt or decrypt text, with an auto-detect mode that uses English letter frequency to recover the likely shift. It is a classical cipher for learning and puzzles — not secure encryption. Runs entirely in your browser.

Category
Developer
Pricing
Free
Privacy
Browser-based
Signup
Not required

References

Privacy

Your data never leaves your browser unless explicitly stated. Caesar Cipher runs entirely client-side — no server upload, no logging, no tracking of your input.

Related tools

JSON Formatter

Format, validate, and minify JSON online. Free, no signup — your data never leaves your browser.

Open tool

SQL Formatter

Format SQL queries online — beautify MySQL, PostgreSQL, SQLite, SQL Server, Oracle, and BigQuery.

Open tool

UUID Generator

Generate UUIDs online — v1, v4, v7, and Nil. Bulk generation up to 10,000. Free, no signup.

Open tool

Password Generator

Generate strong, cryptographically random passwords. Configurable length and character sets — runs in your browser.

Open tool

Build, share, and grow on Zerethon Social

Free signup. Earn points, collect achievements, and connect with creators worldwide.

Try Zerethon free