---
name: "caesar"
section: "6"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/caesar"
---

# caesar(6)

decrypt caesar ciphers

## NAME

**caesar**, **rot13** – decrypt caesar ciphers

## SYNOPSIS

**caesar** \[*rotation*\]

**rot13**

## DESCRIPTION

The **caesar** utility attempts to decrypt caesar ciphers using English letter frequency statistics. **Caesar** reads from the standard input and writes to the standard output.

The optional numerical argument *rotation* may be used to specify a specific rotation value. If invoked as **rot13**, a rotation value of 13 will be used.

The frequency (from most common to least) of English letters is as follows:

ETAONRISHDLFCMUGPYWBVKXJQZ

Their frequencies as a percentage are as follows:

E(13), T(10.5), A(8.1), O(7.9), N(7.1), R(6.8), I(6.3), S(6.1), H(5.2), D(3.8), L(3.4), F(2.9), C(2.7), M(2.5), U(2.4), G(2), P(1.9), Y(1.9), W(1.5), B(1.4), V(.9), K(.4), X(.15), J(.13), Q(.11), Z(.07).

Rotated postings to USENET and some of the databases used by the [fortune(6)](/fortune/6.md) program are rotated by 13 characters.