Screenwriting : Can a logline tell too much of the story? by Brian Aldrich

No. Think who is going to be reading it. Directors, producers other interested in making your script. Would you invest time and money into something you didn't know about.

A logline is designed to get Producers/Directors interested in your script enough to request to see it... It shouldn't hide 3rd act surprises as that may be the very thing they like about your idea... No point being coy with these people.

this is on raindance about loglines http://www.raindance.org/10-tips-for-writing-loglines/

As others have said, A log line sells the story not tells the story. The logline should say what's unique about your story. The last thing you want is for someone to read your logline and say, oh that sounds like ____. No teasers and don't keep it generic, be specific. Who's the protagonist? What do they what? What's at stake? Remember, a logline is not a teaser, it's not what's going to appear on the poster. If you have a hook, sell that hook, make the reader/producer want it.

Every time someone posts a question like this, I post this brief logline overview and example. I picked this up several years ago and then added a few more bits to it. For those who have seen this before. Skip my post. For many writers, loglines are a serious challenge. I suggest several things. First, keep them around thirty words or less, +/- five words. Think of your logline as if you were trying to craft a hit song. You have limited time to grab someone's attention. It’s the first step in a process. The second step is getting someone to read your synopsis. The third step is getting someone to read your screenplay. Without performing the first two steps correctly, the third step will not happen. Think about it this way. If your logline is bland, why would anybody want to read your synopsis, let alone your screenplay? When you write your logline, try to include protagonist, antagonist, obstacles and challenges. Then summarize your story in a sentence or two. Look at this logline from the classic film “The Sweet Smell of Success” “A press agent, hungry to get ahead, is pushed by a ruthless columnist to do cruel and evil things, and is eventually caught in the web of lies that he has created.” The above logline is 32 words. It identifies the press agent who is the damaged protagonist controlled by the antagonist, the ruthless columnist. The logline tells you the consequences of the protagonist’s actions. This is exactly what you may want to consider when writing your logline.

It can't tell too much if you don't let it. As others have said, set up the main character (no name, limit to one specific adjective; in other words not a mental woman, an OCD woman), set up the catalyst and obstacle and if the stakes aren't clear end with those. That tells the arc but not the details. Think, hook, line and sinker.

There aren't enough words...

People probably want to make sure that you have a story before they read your script. And you probably want to make sure that you have a story before you write your script. So IMO, your logline should tell a story. I pretty much see it like this: If I can't tell the story in one or two sentences, then I'm probably not going to be able to tell it in 80 - 110 pages either. (Full disclosure, I haven't written a feature yet. I'm still learning. I'm just saying 80 - 110 pages to make my point.) I wouldn't worry about giving too much away. That probably isn't going to happen in 25 words anyway. I would worry more about telling a story in one or two sentences that entices someone to spend 90 minutes of his/her life reading your script. After that, try to make every beat, scene, sequence, and act entice them to keep reading it. I always use Can't Buy Me Love as an example, because it's the movie that taught me how to write a logline. "A nerd and a cheerleader pretend to date, and the nerd becomes the most popular guy in school. But this popularity changes him for the worst, and he learns to be himself." Set Up, Confrontation, Crisis, and Resolution. A story told in 32 words that could entice someone to read the script.

The most important element of a logline is "the hook." However you summarize your story in one or two sentences..."the hook" must be there in those one or two sentences. The hook is what makes someone say "hmmm....interesting...." and is what makes them want to read a script, or see a film. If there's no hook, then there's no look, and your logline is cooked. Cinema execs have read or heard thousands and thousands of loglines - where is the hook in your story that is actually going to make them want to read it?