A spirited discussion on the Short Mystery Fiction Society list led to several short or longer definitions of the beloved cozy mystery. I collected most of them, and list them here. Some are tongue-in-cheek, some are serious, but all give insight into the genre. I've omitted the writers whose definitions are quoted and edited lightly.
A cozy mystery is one in which the blood is dry before it hits the page.
They are a place for the reader to escape, a place the reader will like being. The language used is soft, not harsh, the people are those the reader would like as neighbors, and the killer has a very good reason--at least in their own head--for doing the deed. That pleasant place where order will be restored.
A cozy is a mystery in which someone gets killed but no one gets hurt.
I think of the word cozies as mysteries to which the word "cozy" applies in two ways.
First, cozy in the sense of comfortable. They're not disturbing to read. Violence happens offstage, sex is only suggested, the language is mild.
Second, cozy in the sense of close and contained. The story takes place in a community of limited size, such as a small town and there is only a handful of suspects.
Life as it should be with a little excitement added in (murder).
There’s a lot of hairsplitting over the definition of a cozy and the difference between cozies and traditional mysteries. The lines are definitely blurred. Basically a cozy has no on-page sex or violence, with little or no profanity (preferably none). They often take place in a small town. I never heard the bit about no one getting hurt. Traditional mysteries are grittier and perhaps more realistic. I would put Agatha Christie’s Jane Marple in the cozy category. Sayers more traditional.
I would also note that cozies have a strong element of female empowerment. The protagonists are busy making a life for themselves, often a new life after a tragedy, and often against the odds. They run businesses and libraries and community theaters, and sometimes families. Their world is disrupted, and they do everything it takes to put it back together. They get sugar done.
"Cozy" is essentially synonymous with "traditional mystery."
I do want to say that although the cozy genre is very heavily weighted towards female protagonists, there are some authors who have done a great job making male protagonists work in a cozy as well. I’m thinking about M.K. Wren’s Conan Flagg series, Jack Ewing’s Primed for Murder, Stephen Humphrey Bogart’s R.J. Brooks mysteries, Matt Witten’s Jacob Burns mysteries and many more.
Cozies have nothing in them that will upset *anybody,* even the most strict reader.
For traditional mysteries, the most important thing is the puzzle.
The level of action and danger varies, and we don't always like the protagonist that much, but the puzzle needs to hang together. The reader gets intellectual satisfaction from the solution of the puzzle.
For cozies, the most important thing is that the reader feels that the protagonist is a friend, and they feel comfortable in their company.
Cozies can have some mild action, and some danger, and they have a puzzle, but all of that is subordinated to creating an emotional bond between the protagonist and the reader.
The reader gets emotional satisfaction from having spent an enjoyable few hours in the company of their friend.
A cozy is a book you can read before going to sleep at night, and still be able to go to sleep at night.
Both cozies and traditionals: no excessive, graphic, gratuitous sex or violence on the page, plus very little or, preferably, no “expletive deleted” words. Usually a small-town setting. Emphasis on backstory, character development, whydunit as well as whodunit.
Difference between cozies and traditionals: in a cozy, the sleuth is always an amateur, generally female. In a traditional, it is a professional, sometimes a police officer, but more often a private investigator, and more often male.
Christie’s Poirot books are traditional; Miss Marple books are cozies.
Someone dies, no one gets hurt.
There’s a lot of hairsplitting over the definition of a cozy and the
difference between cozies and traditional mysteries. The lines are
definitely blurred. Basically a cozy has no on-page sex or violence, with
little or no profanity (preferably none). They often take place in a small
town. I never heard the bit about no one getting hurt. Traditional
mysteries are grittier and perhaps more realistic. I would put Agatha
Christie’s Jane Marple in the cozy category. Sayers more traditional.