The newsletters are titled and usually follow a theme, such as Justin Wolfe’s daily “thank you notes,” nearly all of whose sentences begin with the words “I’m thankful” and which functions as a gratitude journal.

Bucking the stricter limits of Twitter and Facebook posts, these TinyLetters can be any length, and can be seen as an epistolary backlash to the complexity-stunting brevity of social media. Unlike a personal email or postal letter, however, TinyLetters go to multiple recipients, just like that old family newsletter, and a performative element inevitably enters into the composition.

Their creators, though, tend to profess modesty.

“I was a blocked writer and wanted to start writing something that was low stakes and didn’t have to be perfect,” said Ruth Curry, a co-publisher of the independent literary imprint Emily Books.

Ms. Curry’s self-explanatorily titled TinyLetter, “Coffee & TV,” “was for my friends who don’t live in New York, and coffee and TV was a way to organize my thoughts to do something that wasn’t just a diary entry, to keep my powers of observation sharp,” she said. “I try not to overthink it. If I knew it was going to be published, I’d be freaked out and probably not do it.”

Ms. Kreizman began her newsletter, which runs down her weekly media diet, after her book based on her popular Tumblr, “Slaughterhouse 90210,” was published and she still had events and writing to publicize. “Of course I couldn’t just do one promoting myself, because that’s stupid, so it became a way for me to weigh in on all the things I loved that week,” she said.“If it were a ton of work, I would stop — this is a little side thing.”