What does 10/1 mean in a book cipher?

In this mode it means character 1 of reference word 10. Other books and puzzles may use page/line or page/line/word coordinates; those are different conventions and are not inferred.

How are words and characters counted?

Split the pasted reference on whitespace, remove punctuation at word edges and skip tokens containing only punctuation. Count the remaining words from 1. Count Unicode code points within each cleaned word from 1; interior punctuation and combining accents remain characters.

Can I encode a message with this reference?

Yes. Coordinate mode finds exact-case characters in the reference, rotating among repeated occurrences. Spaces in the message become | separators. A missing character is an error. The two word-index modes use their own stated case and punctuation normalization.

Can this find the book or guess an invalid number?

No. It requires the exact reference and convention. Out-of-range or malformed coordinates are refused, and page/line/word triples are unsupported.

Book Cipher Decoder: Word and Character Coordinates

Paste the reference used by the sender. This example decodes 10/1 11/2 12/2 12/2 12/1 to hello: word 10 is honey, word 11 is yellow and word 12 is olive. Both word and character positions start at 1. The word/character mode accepts slash coordinates or whitespace pairs such as 10 1 11 2, and uses | between message words. First-letter and whole-word index modes are separate selectable conventions. The tool does not identify a missing reference book.

Cipher text24 characters

Plain textBook, 12-word reference, word/character coordinates

hello

decode words and code-point characters numbered from 1; split reference on whitespace, strip edge punctuation, keep interior punctuation; exact case; W/C or W C pairs; | between message words; page/line/word triples not supported

10/1word 10, character 1, h
11/2word 11, character 2, e
12/2word 12, character 2, l
12/2word 12, character 2, l
12/1word 12, character 1, o

encode use the same reference, exact case and word/character convention

Each number stands for

Reference text12 words

Method: Book, 12-word reference, word/character coordinates

Characters: 5

Encode: use the same reference, exact case and word/character convention

Numbers point at words in your reference text, or word/character coordinates point at a specific character. Count from 1; use the same reference on both sides.

10/1 means character 1 of word 10. Both positions start at 1. Use spaces between coordinates and | between message words. Edge punctuation is ignored; interior punctuation and accents count. Encoding matches exact case. Page/line/word triples are not supported.

Textbook checks, one per method

Each row is worked by the same code as the stage above. Load puts it in the workbench with its keys.

Caesar, shift 3ABCXYZ
DEFABC
Keyword KRYPTOSKNOWLEDGE IS POWER
DGHVETPST BM IHVTL
Polybius 5 x 5, I and J share cell 24JAM
24 11 32, which decodes as IAM
A1Z26, numbers separated by spaces1 26
AZ
Nihilist, square ZEBRAS, key RUSSIANDYNAMITE WINTER PALACE
37 106 62 36 67 47 86 26 / 104 53 62 77 27 55 / 57 66 55 36 54 27
Book cipher, a 40-word reference text3 17 52
error: word 52 is outside the 40-word reference, and nothing is guessed
One-time pad, key XMCKLHELLO
EQNVZ

Puzzles and teaching, not secrets. These are historical and puzzle ciphers. Caesar has only 25 shifts on A to Z, so the ranked list that Decode shows reads most messages without the key, and keyword, Polybius and A1Z26 text gives way to letter counting. The one-time pad mode shows the arithmetic of a key you type and nothing more: this tool does not make keys and makes no claim that a message stays secret.

Accuracy. Each method follows the convention shown beside it: Caesar shifts count from 0 at the first letter of the alphabet and wrap after the last, the 5 x 5 Polybius and Nihilist squares give I and J one cell, A1Z26 reads 1 26 as AZ, and a book number outside your reference is an error, never a guess. The ranked list of Caesar shifts is an estimate from English letter frequency. These are historical and puzzle ciphers, not modern secure encryption, and the one-time pad mode only shows the arithmetic of the key you type, with no claim that it keeps a message secret.

Common questions

What does 10/1 mean in a book cipher?: In this mode it means character 1 of reference word 10. Other books and puzzles may use page/line or page/line/word coordinates; those are different conventions and are not inferred.
How are words and characters counted?: Split the pasted reference on whitespace, remove punctuation at word edges and skip tokens containing only punctuation. Count the remaining words from 1. Count Unicode code points within each cleaned word from 1; interior punctuation and combining accents remain characters.
Can I encode a message with this reference?: Yes. Coordinate mode finds exact-case characters in the reference, rotating among repeated occurrences. Spaces in the message become | separators. A missing character is an error. The two word-index modes use their own stated case and punctuation normalization.
Can this find the book or guess an invalid number?: No. It requires the exact reference and convention. Out-of-range or malformed coordinates are refused, and page/line/word triples are unsupported.

Each method follows the convention shown beside it: Caesar shifts count from 0 at the first letter of the alphabet and wrap after the last, the 5 x 5 Polybius and Nihilist squares give I and J one cell, A1Z26 reads 1 26 as AZ, and a book number outside your reference is an error, never a guess. The ranked list of Caesar shifts is an estimate from English letter frequency. These are historical and puzzle ciphers, not modern secure encryption, and the one-time pad mode only shows the arithmetic of the key you type, with no claim that it keeps a message secret.