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Caesar Cipher / ROT13

Encode or decode text with the classic Caesar shift cipher. Adjust the shift from 0 to 25 with a slider, jump to ROT13, or scan a clickable brute-force list of all 26 shifts to crack a hidden message.

  • 公開日
  • 最終確認

ツール要約

このツールは構造化された入力を受け取り、サーバーへアップロードせずにブラウザで決定的な出力を返します。

ツール名
Caesar Cipher / ROT13
入力の目的
変換・検証・分析するソースコンテンツを入力してください。
出力の目的
コピー・再利用・デバッグに適した正規化された出力を受け取ります。
入力例
Attack at dawn!
出力例
Nggnpx ng qnja!
12letters+13shift
Non-letters (digits, punctuation) are left untouched.
Show all 26 shifts (brute-force preview)

ツールの紹介

Encode or decode text with the classic Caesar shift cipher. Adjust the shift from 0 to 25 with a slider, jump to ROT13, or scan a clickable brute-force list of all 26 shifts to crack a hidden message.

ツール概要

The Caesar cipher shifts each letter a fixed number of positions through the alphabet. ROT13 is the well-known case where the shift is 13, which makes it self-inverse — encoding twice returns the original. Digits, punctuation, and spaces pass through untouched. This tool converts live as you move the slider, includes a ROT13 preset and an Invert button to flip the shift for decoding, and shows every one of the 26 possible shifts so you can pick the one that turns ciphertext into readable English. It is a classical cipher for puzzles and learning — it offers no real cryptographic security, since trying all 26 shifts breaks it instantly.

ユースケース

  • Hide a spoiler or answer with ROT13 the way forums do
  • Create or solve a Caesar-cipher puzzle for a class or escape room
  • Brute-force an unknown shift to reveal a hidden message
  • Demonstrate how a substitution cipher works while teaching cryptography
  • Quickly encode a short note that only needs casual obfuscation

入力／出力の例

ROT13 (shift 13). Punctuation is left unchanged.
入力の目的
Attack at dawn!
出力の目的
Nggnpx ng qnja!
Decoding a shift of 3 (invert to -3).
入力の目的
Khoor Zruog
出力の目的
Hello World

よくある質問

Is the Caesar cipher secure?+
No. It is trivially broken by trying all 26 shifts — exactly what the brute-force panel does. Treat it as a learning or puzzle tool, never as real cryptography.
How do I decode a message?+
Use the Invert button to flip your current shift, or open the brute-force list and click the row whose output reads as normal text.
What is ROT13?+
ROT13 is a Caesar cipher with a shift of 13. Because the alphabet has 26 letters, applying it twice returns the original text, which is why forums use it to hide spoilers.
Does it shift non-English letters?+
The shift applies only to the 26 letters A–Z (in either case). Digits, punctuation, spaces, and characters from other alphabets pass through unchanged.

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