Cipher wiki
The solver above breaks the puzzle; the wiki explains what was going on underneath. Fifty cipher articles — one per cipher in the registry, each with a worked example generated by running the cipher itself — plus long-form guides and a three-part history of codebreaking. Every article page carries the same solver, so you can test each idea on a real puzzle as you read.
Start here: the wiki main page
Browse all fifty ciphers by family, catch the featured article, and read a ciphertext's alphabet, frequencies and index of coincidence before you guess at the cipher.
Open the cipher wiki →Famous Unsolved Ciphers & Scripts
Open problems deserve sources, scope, and an honest standard of proof.
Read the article →The Caesar Cipher
A rotation so small it teaches nearly every idea behind classical cryptanalysis.
Read the article →The Vigenère Cipher
Several Caesar ciphers woven together by a keyword — clever, historic, and breakable.
Read the article →Substitution Ciphers
A colossal keyspace with a very human leak: the shape of language remains.
Read the article →The Playfair Cipher
A grid of 25 letters turns single-letter statistics into a pairwise problem.
Read the article →The M-94 Wheel Cipher
Twenty-five mixed alphabets on a spindle: the US Army's field cipher, and how 25! disk orders still fall.
Read the article →A History of Codebreaking
Every technique in this solver has an inventor and a date. Here they are.
Read the article →The Codebreakers
Who broke what, when, and what it cost them.
Read the article →Famous Ciphers
The ones that changed history, and the handful nobody has read yet.
Read the article →All fifty cipher articles
Shift, substitution, polyalphabetic, transposition, polygraphic, wheel, XOR, codes and encodings — one encyclopedia page each, generated from the solver's registry.
Browse every cipher →What this does
Most cipher tools ask you to pick the cipher and supply the key. That is fine when you already know both, and useless when you are staring at a block of gibberish from a puzzle box, a geocache, an escape room or a CTF challenge. This one starts from nothing: it measures the text, forms hypotheses about what produced it, searches the keyspaces, and scores every candidate plaintext against a statistical model of English.
How it decides
Three signals do most of the work.
Index of coincidence
The probability that two letters drawn at random from the text are the same. English
sits near 0.067; random text sits near 0.038. A monoalphabetic
cipher such as Caesar or a substitution keeps the value near English because it only
relabels letters. A polyalphabetic cipher such as Vigenère flattens it. That single number
splits the search space roughly in half before any key is tried.
Trigram scoring
Every candidate plaintext is scored by the average log-probability of its three-letter
sequences under an English corpus model. THE, AND and
ING are common; QKX is not. This is what lets the tool pick the
correct Caesar shift out of 26 without a human reading them, and what guides the
hill-climbing search for substitution keys.
Word hits
Trigram scores alone can be fooled — a hill-climber will happily produce text that looks English-shaped without being English. So the final ranking also counts how many real words appear, weighted by length, which breaks ties between near-identical candidates and catches single wrong letters in a recovered key.
Layered puzzles
Puzzle setters stack things: base64 around hex around a Caesar shift. After trying the direct ciphers, the solver tests whether the text is a valid encoding, unwraps one layer, and runs the whole process again on the result, up to three layers deep. The decode chain is shown with the answer so you can see exactly what was done.
A worked example
Press the Layered sample above. The input looks like base64. Decoding
it gives hex; decoding that gives letters that still are not English; the index of
coincidence says monoalphabetic; a 26-shift sweep finds the answer. The tool reports the
chain base64 → base16 → caesar along with the key it recovered.
Frequently asked questions
Do I need to know which cipher was used?
No. The solver characterises the text first — index of coincidence, entropy, character set — then tries every cipher it knows and ranks the candidate plaintexts with an English trigram language model. You just paste and press the button.
Is my ciphertext uploaded anywhere?
No. There is no server. The entire solver, including the language model, is JavaScript that your browser downloads once and runs locally. You can disconnect from the internet after the page loads and it still works.
Which ciphers can it break?
Caesar and ROT13, Atbash, affine, the periodic family — Vigenère, Beaufort, Variant Beaufort, Porta, Gronsfeld, Trithemius and autokey, all with automatic key recovery — plus monoalphabetic substitution, rail fence transposition, single-byte XOR, and the encoding layers base64, hex, binary, decimal bytes, Morse and reversed text, including several of those stacked on top of each other.
Why did it fail on my text?
The most common reasons are that the text is too short (under about 40 letters there is not enough statistical signal), the plaintext is not English — this browser build scores English only — or the cipher is outside the set above. Longer ciphertext is dramatically easier to break than short ciphertext, and the full desktop version adds French, German, Italian, Latin and Spanish models for non-English plaintext.
Can it break modern encryption like AES or RSA?
No, and neither can anything else you will find on the web. This tool targets classical and puzzle ciphers. Properly implemented modern encryption is not breakable by frequency analysis or key search.