What are the features of a well-written puzzle?

Question

When making a new puzzle, the average person is usually faced with a hard problem of guaranteeing quality.

I want to know some key points and ideas, for beginners and experts alike, to keep in mind when creating their puzzle, because a good puzzle must be well-polished. What are some features of good puzzles that apply broadly to a wide range of types of puzzles? I would imagine careful management of difficulty - something like the requirement of play-testing - would be an aspect to consider, for example.

Answerers are encouraged (but not required) to provide examples of features, common mistakes, and ways to improve a puzzle.

Answer 1

From my experience as corrector of text puzzles on a Russian puzzle site 3 features are required for a puzzle to be liked by solvers (in order of importance): motivate, be correct, do not be straightforward.

1. It is Interesting. It must have something unusual. This is clearly the most important, if a reader does not expect to to get a new knowledge and experience he won't even try to solve it most probably. For example, x^2-2x+1=0 would not be a puzzle at all, just because it is standard quadratic equation.
   So, what can be unusual about a puzzle?
   1.1. Unexpected, beautiful fact to prove. For example, draw a shape which can be cut both on 3 and 4 equal triangles. Or, a puzzle about passenger, which comes to a bus stop at a random moment and most often meet his bus, that goes into wrong direction.
   1.2. It's answer seem to be impossible. For example, a puzzle which asks how to measure diagonal of a brick in one measurement with solid ruler, or prisoners problem.
   1.3. It's answer can seem to be too obvious (but this obvious answer must be wrong of course). For example, can whites win in this position?.
   1.4. It can be about unusual properties of well know objects. For example, "Is it possible in a Cartesian coordinate system to position a regular tetrahedron so that all its vertices lie at the points with integer coordinates?".
   1.5. It can look too complex to solve (but one should know that it is a puzzle, not a practical question and it has found, simple solution). For example, ants on a stick puzzle.

2. It's task is Easy to Read and Understand. At least, the understanding of the task must require much less time than the solution itself.
   To be like this it must be:
   2.1. complete. It must have all special information reader needs. And it must allow only one interpretation. But, note that there are well know facts, these don't have to be included in the formulation of the puzzle, and nobody can create a puzzle that can not be misunderstood.
   2.2. compact, any word you put in you must think though, you must ask yourself whether it is really needed there.
   2.3. tested. It must be read by several people, different people always see one thing differently, the author alone can't predict all problems.
   2.4. reading process should be pleasant. So you better check you spelling, structure and order of phrases. Also, it is always nice to find appropriate "interface" for the idea behind a puzzle, all puzzles can be formulated in a strict mathematical language, but if you find real-life situation, that fits your idea the puzzle would became much easier to remember and understand.

3. It's Solution is Interesting. The solution should have a new idea behind it. It's very nice when it simple to understand and compact, but meanwhile is hard to find (not straightforward).

Answer 2

A well-written puzzle is hard to define. Even a decent puzzle is hard to define. Instead, I'll say some signs of a poor puzzle.

Impossible to confirm

If there are unintended solutions that look just as good as the intended one when explained, you're no longer solving a puzzle, you're trying to guess what's in the mind of the asker. The right solution should be clearly correct if explained, and not just for sounding clever, but for fitting the given conditions better than any alternative. Moreover, no wrong solution should feel this way.

Just a cipher or encoding

"Codes" that are just a short string of numbers and letters aren't fun. You can't do anything better than throw random solution attempts and check if English comes out. There's so many to try and no way to tell which is right except trial and error.

Take the following fictional example (not a real message).

ADOOGF
SORPPF
FFLGMQ
EPGKBN
EPEKGF
GFPELW

Maybe you Caesar shift each row by a different index. Maybe you split up the grid into 2x3 blocks and interpret them as Braille with vowels being dots. Maybe you convert each letter to ASCII and read down the columns to get numbers and ... There's way too many things to try. Composing multiple codes without intermediate confirmation makes it even worse.

If you're going to write a code, include some hints as to the mechanism used, either through direct clues, thematically in flavortext, or in some apparent feature of the ciphertext.

Loads of pointless backstory

If the entire backstory is "One day I was talking to my friend. [3 paragraphs omitted] He said he'd give me a cookie if I solve the following puzzle", then there's no need for it. Just post the puzzle.

If the backstory has a few clues for the puzzle, but has way more non-clue text, it will do more harm than good as solvers will latch onto red herrings.

Even worse is if the backstory contradicts the idea of the puzzle. Why and how did the victim write a puzzle cluing her murderer with her dying breath?

Invisible clues

If the key to a puzzle is hidden in invisible characters or in the edit history, then someone will either find it or not. And someone who doesn't think to check will waste their time fruitlessly trying to make something of what they see, unaware that they have no chance at getting anywhere.

Loads of distraction

A puzzle that is only hard because it includes lots of irrelevant distracted content is a bad puzzle. It wastes the solvers' time, as they are likely to find loads of things they think are clues among the filler. Solvers don't want to search for a needle in a haystack -- or a needle in a stack of needles. If your puzzle is "too easy" without intentional red herrings, then it's not much of a puzzle.

(This doesn't apply to puzzles designed around this principle like spot-the-clue mysteries and word searches.)

Intentionally misleading

http://xkcd.com/169/

If your puzzle is intentionally worded so that any reasonable solver would interpret it wrong, that's not a puzzle but an exercise in mindreading. An answer that's technically correct under some twisted interpretation of the conditions in not an answer, and just invites other misinterpretations that are arguable but equally bad.

Wordplay and circumspect hints are fine, as long as it's a type of puzzle where a solver would expect such.

Why did he do X?

Why did the man kill himself after eating seagull meat? Why did the teacher say "you're lying"? Why did the police officer arrest the woman in green?

I don't know why; I'm not them. I can think of lots of reasons it could have happened. You have a story for it, and I can make up a story too. You're really asking me to guess your story. Your story probably involves some clever trick, but cleverness isn't correctness.

Tacked-on busy-work

For example, "plug in the result to [this URL] to get the answer."Or, "take the answer to the riddle and use it as a key to solve the cipher to get the solution." Why? Decoding a cipher with the key is a purely rote exercise. It's not fun. Or if you can solve it without the key, that makes the earlier steps moot.

A puzzle can take multiple steps, but they should feel cohesive and justified on their own. It's inevitable to have bits that the solver just needs to execute once they know what to do, but don't make the puzzler do work for the sake of doing work. If you need a follow-the-instruction step to "pad out" the puzzle, you should instead improve the puzzle so that it doesn't need it.

Answer 3

(More challenges! Otherwise this will just go to the graveyard)

There is no black-or-white rule for saying what is or not a well-written puzzle.

You should consider those criteria:

• Is it logically solvable? I.E. There is some logic sequence of steps that leads to the solution.

• Is it practically solvable? I.E. The solution do not requires brute forcing a ridiculous large set of possible solutions or an enormous quantity of guesses.

• Is it well redacted in clear and correct English? Except if some part is not on purpose (I.E. not by accident), puzzles with bad grammar, bad punctuation and typos may mislead eventual solvers in ways that they are not supposed to be misleaded, and make them harder to understand.

• Is it interesting? Many puzzles are boring and annoying to find an answer. Make them invite people to think about solving them instead of scaring.

• Is it cohesive? The parts of the puzzle should bends together elegantly and naturally. Puzzles which have non-red-herring subparts that has few to no relation with the rest are IMO not well designed.

• Has it the right degree of difficulty? Puzzles that are too hard may frustrate people and be rendered as unsolvable without major give-away hints or brute-force methods. Puzzles that are too easy may be disappointing both for who asks and for who answers.

• Is it balanced? Following this answer on meta from Travis Kindred, there are basically three types of puzzles: Calculation, Interpretation and Assumption. I will add that most puzzles tends to be a mixture of different proportions of those components rather than being purely one of them. The component "Assumption" is normally (but not always IMO) bad. The others are normally ok.

• Is it concise and detailed? The text used to describe the puzzle should not be too long, complex and hard to mentally parse, i.e. it should be concise. OTOH it should not be too short, oversimplified and unclear, i.e. it should be detailed. Some puzzles might need long sections of texts narrating what happened, that is ok. But if many parts of the texts is superfluous or unnecessarily complicated, it should be redacted more concisely. If many parts are not clear or vague, then it should be more detailed. I.E. The size and the content of the text should be just right, with not too much nor too few.

• Is it complete? Is all the needed information inside the puzzle? If yes, then it is ok. If not, does it make clear that people should look for some information elsewhere? If not, then it is bad. If yes, do it gives a reasonable clue to where to find additional information? If not, it is bad. If yes it is ok.

• Is it simple and compact? As suggested by @klm123 (and directly quoting him): "a puzzle that frustrate people at first look, but has impressively simple solution when you get right idea is the most brilliant ones".

Answer 4

Here's what I think. Note that some points overlap with other answers.

• Logical steps: Is each solve step clear and logical, or does it rely on unstated assumptions or unreasonable interpretations of the clues?
• Confirmation: Once you've solved a step, is there a good way of telling whether you're on the right track?
• Fair search spaces: If the puzzle is hiding a message via whitespace between words or Markdown in a post, then unless the formatting is clearly abnormal then a hint is a must. If the puzzle requires brute forcing all permutations of a Rubik's Cube... then that's just unfair.
• No artificial difficulty: Don't include anything that requires purely time and no brains. "My puzzle is too easy, maybe I'll just encode the first clue paragraph in Morse code and make them decipher it." Please, no — that's just no fun.
• Minimise red herrings: Unusual surface readings (e.g. for cryptic crossword clues) are fine, but red herrings placed for the explicit purpose of leading someone down the garden path are not.
• Pay attention to the details: If something is irrelevant to the puzzle, then order it in some way such that the irrelevance is clear. For example, the order the words are given in a word search rarely matters, so order them alphabetically so nobody will try to find patterns in the word order. Also check your spelling and grammar — if something seems off, then people might end up thinking that it's relevant.
• Do your research: Unfortunately, even good puzzles written with the intention of having a single clear answer can fall into this trap. Maybe you have two clues saying "Morse" and "insect", telling people to interpret something as Morse code to get an insect as the answer. Well I'm sorry — as clear as the instruction may seem, Serenity is a firefly that communicates in Morse code and a Vibroplex is a semi-automatic Morse key that became known as a "bug". Think about how other people might interpret your clues, and try to get a feel for other possible interpretations out there.
• Consider your target audience: If you have a puzzle that requires specialist knowledge (e.g. programming, advanced mathematics) and you don't expect most of your potential solvers to have that knowledge, then try to make sure that the knowledge required is 1) minimised, 2) easily searchable and 3) easy to understand quickly.

Answer 5

I posted this answer here, and xnor suggested I also post it on this question.

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An article on this topic that I've found very useful is this one.

A brief summary:

• Puzzles should be compelling. Provide something that hooks the solver, and makes them want to solve the puzzle.
• Avoid red herrings that cause people to spend significant time going down the wrong path without getting closer to a solution.
• If the puzzle requires an intuitive leap, it's better if that leap is not too difficult. A puzzle with an easier "intuitive leap" and a hard "processing" section is better than the opposite.
• A puzzle should provide some indication of progress. If there are multiple steps, it should be obvious when one step has been correctly completed. A multi-step puzzle with no feedback along the way can be nearly impossible.
• A puzzle should consume all the information provided. There should not be extraneous information that doesn't help find a solution; it will make the solver feel like something has been missed.
  • A puzzle that reuses information (information is interpreted in two different ways to provide two different steps to solving the puzzle) is especially clever.
• A clever tool can be recursion. If the first step of the puzzle leaves you with a certain amount of information, re-applying that step can be the way to get the final solution.
• A theme helps hold the puzzle together and makes it more compelling to the solver. Sometimes tying all elements of the puzzle into one common theme can be difficult, but the more you can do it, the more interesting it is to the solver.