Great resources. Thank you Lee.

With the caveat that formulaic is usually bad, the
most elegant formula for creating a great logline that I’ve seen is:

“When [INCITING INCIDENT], a [SPECIFIC
PROTAGONIST] must [OBJECTIVE], or else [STAKES].”

Insert your script’s particulars with
“extreme brevity” at the brackets.

Then…

One piece of advice someone once mentioned is that
a good logline is a hook and a promise.

I, myself, have gone by the rule tell the first
two acts and tease the third.

And no hype–they see through it.

Here’s a trick someone told me to devise a
logline for a screen story:

Ask 3 or 4 questions starting from the end of your
story and going back to the beginning.

How can Marty come back from the past? (He has to
reunite his parents)

Why did he have to reunite his parents? (Because
he has changed the past which drove them apart)

Why did he change the past? (Because he accidently
distracted his mother from noticing and falling in love with his father)

Why did he find himself in the past? (To save his
skin using the invention of a crazy scientist)

So to make it a logline you combine the answers:

“A young man, to save his skin, hides in the
past thanks to the invention of a crazy scientist. He meets his future parents
and accidently distracts his mother from noticing and falling in love with his
father. So he is forced to bring them together or he will cease to exist.”

Then you boil it down to get to one or two
sentences:

“A young man is transported to the past where
he must reunite his parents before he and his future are no more.”

Finally, here are some great articles on loglines:

https://twoadverbs.site.aplus.net/loglinearticle.htm

https://www.inktip.com/tips-loglines.php

hhttps://johnaugust.com/2005/writing-loglines-for-a-comedy

https://www.writersstore.com/writing-loglines-that-sell

https://scriptshadow.blogspot.com/2011/06/scriptshadow-special-how-to-craft-damn.html#disqus_thread

So feast on that, scribes!