Hard-boiled mysteries typically take place in the city with a loner detective who is this side of broke. The hard-boiled detective will face getting assaulted, kidnapped or even murdered to achieve justice. Expect violence, gritty language and possibly graphic sex (some writers who are happy with gore pull the curtain when the romance gets too hot.) Even though morality is ambiguous in a hard-boiled story, justice will prevail.
Not necessarily so with noir mysteries. Noir dwells at the far end of hard-boiled. The purest noir stories are told from the criminal’s point of view. Fate plays an important role, and there’s never a happy ending.
Soft-boiled mysteries are strictly small town. The reader won’t get a glimpse of the murder victim. If there’s violence beyond the murder (and often there isn’t) it will happen off-page. Soft-boiled characters don’t swear or use slang. When the characters have sex it’s so off the page, it happens in a different part of the library.
Just as noir stories dwell at the far end of hard-boiled stories, the cozy dwells at the far end of soft-boiled. The great aunt of the cozy is Miss Marple, and just as she had her knitting, the modern cozy sleuth has her cats, her catering business, or her ability to feng shui her solution to the murder.
Noir to cozy detectives exist on a spectrum with stories falling between hard-boiled and soft-boiled. Aren’t you a little curious what I write? Hard-boiled. Definitely.