Cipher Identifier

Paste a mystery code to see its letter frequencies and index of coincidence, a ranked list of likely ciphers and encodings, and one-click decoding.

Paste any ciphertext and the Cipher Identifier analyzes it: length, character set, letter frequencies compared with English and the index of coincidence (IoC), the chance that two letters picked at random are the same. English text has an IoC near 0.067 and random letters near 0.038. From these clues it ranks likely encodings and ciphers, each with a confidence level and the reasons for it, and decodes the ones it can. For example, 8-5-12-12-15 is identified as A1Z26 and decodes to HELLO, and WKH VHFUHW is flagged as a Caesar shift of 3 that reads THE SECRET. It checks for Base64, hexadecimal, binary, Morse, A1Z26, decimal ASCII, Caesar and ROT13, Atbash, reversed text, rail fence, other transpositions, substitution and Vigenère. Below about 50 letters, treat the result as a hint.

Mystery text

Try an example:

Most likely

1. Caesar cipher (shift 3)
High confidence (84%)
- Shifting every letter back 3 places gives English-looking text.
- Letter frequencies have the English shape, moved along the alphabet.
Decoded (shift 3)
The treasure is buried beneath the old oak tree.
Open in the Caesar tool

Confidence is a heuristic from letter statistics and test decodings, not a guarantee. Pigpen and other symbol ciphers can't be pasted as text: decode them with the Pigpen Cipher Translator.

Statistics

Characters: 48
Letters: 39
Uppercase / lowercase: 1 / 38
Digits: 0
Spaces: 8
Punctuation: 1
Other symbols: 0
Distinct symbols: 16
Distinct letters: 14 of 26
Words: 9
Average word length: 4.4
Character set: Letters and punctuation

Index of coincidence

0.0864

Random letters ≈ 0.0385 · English ≈ 0.0667. Substitution ciphers keep the English value; Vigenère and other polyalphabetic ciphers move it toward random.

Chi-squared against English letter frequencies

189.2

Lower means the letters are distributed like English. Plain text and transposition ciphers score low; shifted or substituted alphabets score high.

Letter frequency

Bars: this text · dashed line: English

Most common: H 23.1%, W 12.8%, U 10.3%, D 7.7%, K 7.7%, E 5.1%. In English the most common letters are E, T, A, O, I and N.

Common use cases

Work out what kind of code an escape room or puzzle hunt clue uses
Decode Base64, hex, binary or Morse without knowing which it is
Recover a Caesar shift, rail fence count or Vigenère key automatically
Check the letter statistics of a cipher you're solving by hand

How to use

Paste the mystery text into the box.
Read the ranked list: each guess shows a confidence level and why it was suggested.
Where Tekscape can decode it, the result appears under the guess. Use Open in tool to adjust the settings.
Use the statistics panel (letter frequencies, IoC) for ciphers that need solving by hand.

FAQ

How accurate is the cipher identifier?

It's reliable for encodings with a distinctive alphabet (Base64, hex, binary, Morse) and for Caesar, Atbash, rail fence and Vigenère messages of about 100 letters or more, because it confirms those guesses by decoding. Short texts and ciphers it can't decode get lower confidence. It doesn't check for ciphers such as Playfair, Enigma or book ciphers.

What is the index of coincidence?

The probability that two letters drawn at random from the text are the same. English is about 0.067 and evenly spread random letters about 0.038. A substitution cipher keeps the English value, while Vigenère pulls it toward random, which is how the tool tells them apart.

Why can't it decode a substitution cipher?

A monoalphabetic substitution has 26 factorial (about 4 × 10^26) possible keys, and solving one means working from letter frequencies and word patterns. The tool shows the frequencies to get you started but doesn't solve it automatically.

Can I paste pigpen or other symbols?

Not usefully: symbol ciphers don't map to text characters. For pigpen, use the Pigpen Cipher Translator's decode mode and click the symbols you see.