Gravity Falls ciphers and codes: how to decode the show's messages yourself

Gravity Falls hides plaintext inside the show deliberately, and most of it is decodable with methods that are taught in a single afternoon. This page explains the methods the series and its supplementary material use, and how to test a decode rather than trusting a fan list. For the in-universe lore around the journals, see Journal 3. For the real-world hunt that used the same techniques, see the Cipher Hunt.

Caesar shift

A Caesar shift moves every letter a fixed number of positions through the alphabet and wraps around. Shift by 3 and JBMXVHW becomes MASTER. This is the show's most common trick, and it appears in the series, in Journal 3, and in the Cipher Hunt announcement tweet, where a run of red letters decoded to a country name only after a minus-3 Caesar pass.

How to test one: write the ciphertext twice, once shifted forward and once backward, and look for common words. If nothing readable appears, try every shift from 1 to 25. Caesar is broken by frequency analysis, so a long message will crack almost immediately.

Atbash

Atbash maps the alphabet onto itself, A to Z, B to Y, C to X, and so on. It is its own inverse, which is the fastest way to check it. The Cipher Hunt's first clue used a minus-3 Caesar and Atbash in combination, which is a good reminder that the show stacks methods rather than picking one.

A1Z26 and simple substitution

A1Z26 replaces each letter with its alphabet position, so the word BILL becomes 2-9-12-12. Substitution swaps the whole alphabet for another arbitrary alphabet. Both are easy to recognise once you know them: A1Z26 messages are mostly numbers, and a substitution message preserves the same letter-to-letter pattern as English, so the pattern of a frequent short word like THE or AND will stand out.

Vigenere

Vigenere is a Caesar shift that uses a repeating keyword, one letter at a time. It looks uncrackable until you notice the keyword length, and the classic test is the Kasiski examination, where you look for repeated trigrams and measure the distances between them.

Polybius square

A Polybius square arranges the alphabet in a 5 by 5 grid and encodes each letter as a row-column pair, usually written as two digits. The Cipher Hunt's final clue required a Polybius square: fans had to read the branches and knots in the background of the statue image as coordinate pairs and work out which variant of the square was in use. Only after constraining the answer to a place name ending in OR did "REEDSPORTOR" surface.

Hexadecimal

The sixth Cipher Hunt clue was a crude drawing of Bill Cipher beside a series of hexadecimal values that had to be converted to decimal before they read as coordinates at all. Hexadecimal is not a cipher, it is a number base, but the show uses it to make a set of coordinates look like noise.

Why the show bothers

There is a deliberate thematic reason. The journals are in-universe objects that people wrote for other people to read, and the show treats decoding as an activity with real stakes: characters break into rooms, open lockers, and solve puzzles to get information. It also gives the audience a mechanic that rewards attention, and it is why the franchise continued into books and a real hunt built on the same techniques.

Verifying what you decode

Two habits will keep you out of trouble. First, decode rather than transcribe: if you cannot reproduce a message from the raw ciphertext with a stated method, you do not have the answer yet. Second, keep fan lists as a starting point rather than a conclusion, because the show includes deliberate red herrings and joke messages that decode to nothing at all. If a message is meant to be solvable, the decoded text will be English and will say something in character.

For character-level context on who is writing these messages and why, see the character reference and the Bill Cipher explainer.