Codebreaking 101 · Part 1 of 8. A friendly, no-maths introduction to cryptograms for brand-new puzzlers. A new part arrives every Wednesday.
Puzzle books are having quite a year. Somewhere right now, someone is opening their very first cryptogram book, staring at a page of scrambled letters and quietly wondering whether they’ve bought a puzzle or a ransom note.
If that’s you: welcome. Pull up a chair. Pour the tea. By the end of this note you’ll know exactly what a cryptogram is, the three house rules every cryptogram follows, and you’ll have cracked your first one with me. No maths, no jargon, no secret handshake required.
So what is a cryptogram?
A cryptogram is a short message written in a very simple code. Every letter of the alphabet has been swapped for a different letter. That’s the whole trick.
Codebreakers call this a substitution cipher. It sounds grand, but it only means “a swap code”: one letter substitutes for another. If the code says that every A becomes Q, then the word CAT might come out as LQX.
Your job is to work backwards: look at the scrambled message and figure out which real letter is hiding behind each code letter. Think of it as unmasking a room full of letters at a masquerade ball. Everyone is in disguise, but they can’t hide their shape, their habits or the company they keep.
The three house rules
Almost every puzzle cryptogram, including the free Daily Cryptogram on this site, plays by the same three rules. Learn these and you’re already halfway in the door.
- A swap is a swap for the whole message. If code letter X stands for E once, it stands for E every single time. Crack one letter and you’ve cracked it everywhere it appears.
- No letter stands for itself. A code letter M is never a real M. It’s a small rule, but it rules things out, and ruling things out is what detectives do best.
- Spaces and punctuation stay put. Word lengths, commas, full stops and apostrophes are left exactly where they were. They’re not decoration. They’re evidence.
What you’ll need
- A pencil and an eraser. Not a pen. Even seasoned codebreakers change their minds.
- A little alphabet list along the edge of the page, so you can cross off real letters once you’ve placed them.
- Five quiet minutes. Tea optional but strongly encouraged.
Your first case: let’s crack one together
Here’s a tiny cryptogram I wrote just for this lesson. The code letters are in capitals, just like you’ll see in a puzzle book:
XZXLS QMJX TEV E AXS.
Don’t panic. Let’s look for evidence, the way a detective walks into a room and notices the one muddy boot print.
Clue 1: the lonely letter. See that word on its own, E? In English, a one-letter word is almost always A or I. So code E is probably real A or real I. (We’ll lean on this trick a lot in Part 2.)
Clue 2: the repeat offender. The code letter X turns up four times, twice in the very first word. Letters that show up a lot are often the common ones, and the most common letter in English is E.
Clue 3: the shape of the first word. XZXLS has five letters, with the first and third the same. Now try your guesses: if X is E, the word looks like E_E__. What five-letter word starts that way?
Have a go before you open the envelope. Fill in what you’re sure of, pencil in what you suspect, and see whether the rest of the message starts to blush and confess.
Open the sealed envelope: the solution
The message: EVERY CODE HAS A KEY.
How it falls into place:
- The one-letter word E is A. (Could it be I? Then the message would read “EVERY ____ _I_ I _EY”, which no one has ever said on purpose. A is the better bet.)
- X is E, so the first word reads E_E__: that’s EVERY. Now Z = V, L = R and S = Y.
- The last word is AXS with A unknown: _EY. With the message so far (“EVERY ____ _A_ A _EY”), KEY fits nicely.
- The second word, QMJX, is now ___E, and the third, TEV, is _A_. “Every code has a key” clicks into place, and every code letter is consistent.
The full key we found: E=A, Q=C, J=D, X=E, T=H, A=K, M=O, L=R, V=S, Z=V, S=Y.
Notice something? No code letter stood for itself. House rule two, quietly doing its job.
Feeling brave? A slightly longer one
This one’s a step up: longer, with a comma for company. One hint to get you started: the three-letter word that appears twice is the most common word in English.
MDT ORMGTC YJY BLM YL JM, ORM DT ZBLQE QDL YJY.
Open the sealed envelope: the solution
The message: THE BUTLER DID NOT DO IT, BUT HE KNOWS WHO DID.
- The most common English word is THE, so MDT is THE: M = T, D = H, T = E. (The other three-letter word that appears twice, YJY, has a repeated first and last letter, so it can’t be THE.)
- That makes DT “HE” and JM “_T”, and a two-letter word ending in T is very often IT: J = I.
- YJY is now _I_ with the same letter at each end: DID. So Y = D, and YL is “D_”: DO, so L = O.
- BLM is “_OT”: NOT. ORM is “__T” and ORMGTC is “__T_E_”. A butler, of course: BUT and BUTLER.
- That leaves ZBLQE QDL: “_NO__ _HO”. He KNOWS WHO did it. Naturally. Butlers always know.
What just happened (and why it works)
You didn’t guess. You noticed things: a lonely one-letter word, a letter that kept turning up, the shape of a word. Each small discovery unlocked the next, because every swap stays the same across the whole message. That snowball is the whole joy of a cryptogram, and the next seven parts of this series are really just more ways to start it rolling.
If you’re curious whether all this puzzling does your brain any good, I’ve looked at what the research actually says (with suitably modest conclusions) in Are Puzzles Good for Your Brain?
Coming up in Codebreaking 101
- What is a cryptogram? (you are here)
- The tiny-word trick: A, I, THE and AND
- Apostrophes and letter patterns
- Letter frequency, without the maths
- Double letters and word shapes
- Stuck? What real codebreakers do next
- Your first full-size cryptogram, start to finish
- From beginner to Armchair Detective
Your next move
Try today’s free Daily Cryptogram. It’s a line from classic detective fiction, and if you get stuck you can reveal a letter (up to three) or switch on “Show mistakes” while you learn. No one’s keeping score but you.
And when you’d like a whole evening of codes, my cryptogram books in The Armchair Detective Casebook series are made for curling up with. True Crime Cryptograms is a lovely place to begin.
Want new cases before anyone else? Join The Case File Letter, my little dispatch of fresh puzzles and book news.
See you next Wednesday for the tiny-word trick. Bring your pencil.
— Ivy
Ready for a real case?
Try today’s free Daily Cryptogram, or pick up a casebook.