ROT13 is the internet’s favorite lightweight way to obscure spoilers, answers, and puzzle hints — and the Caesar cipher behind it is one of the oldest encoding tricks in history. This tool encodes, decodes, and brute-forces both.
What Is the Caesar Cipher / ROT13 Tool?
This tool shifts each letter in your text by a configurable amount (a classic Caesar cipher), with a dedicated ROT13 shortcut for the fixed 13-position shift most commonly used online, and shows all 25 possible shifts at once so you can spot the correct one for an unknown-shift message.
How to Use It
- Open the tool at /tools/caesar-cipher.
- Type or paste your text.
- Set a shift value, or click the ROT13 shortcut.
- Scan the “all 25 shifts” panel if you’re trying to decode a message with an unknown shift.
Key Features
- Configurable shift from -25 to 25, automatically normalized with a modulo-26 wraparound.
- One-click ROT13, the internet’s most common Caesar cipher variant.
- Brute-force panel showing every possible shift simultaneously — useful for decoding a message when you don’t know the key.
- Non-letter characters pass through unchanged, matching the traditional Caesar cipher definition.
When to Use This Tool
- Encoding a spoiler or puzzle answer the classic ROT13 way.
- Decoding a Caesar-shifted message when you don’t know the shift value.
- Learning classical cryptography and why simple substitution ciphers are trivially breakable.
Try It Now
Open Caesar Cipher / ROT13 directly, or press ⌘K and type the tool name from anywhere on the site.
Part of the Security & Validators collection on WebdevToolbox — free, browser-based developer tools with no login required.