An app description is crucial in promoting your app. It’s the first point of contact with potential users. As such, it should give them a quick overview of what the app can do and what value it can add to the user experience.

There are no hard and fast rules in writing a great app description, but there are things that can be done to make the app stand out from a crowded app marketplace. The best way to learn how to write an effective description is to look at some examples that deliver a compelling pitch.

Look at the app description for Plants vs. Zombies (PvZ). You might think that something as insanely popular as PvZ would not bother with a description. On the contrary, it is a shining example of a great app description:

Get ready to soil your plants as a mob of fun-loving zombies is about to invade your home. Use your arsenal of 49 zombie-zapping plants — peashooters, wall-nuts, cherry bombs and more — to mulchify 26 types of zombies before they break down your door.

Plants vs. Zombies™ was spawned from the fertile minds that created Bejeweled®, Peggle®, Zuma® and Bookworm®.

Why is this effective? It’s snappy, fun, exciting and it just makes you want to spend the entire weekend playing the game! It quickly captivates the audience who happens to be enamored by the pop culture phenomenon known as zombies.

The use of phrases that ties up with the overall theme is just pure genius. It also incorporates game characters, features, awards, and related games.

CalorieKing Food Search is another great example:

Need a quick and easy way to check calories, carbs and fat? The CalorieKing Food Database is America’s best and most reliable. Trusted by health professionals everywhere, it contains over 70,000 foods and includes 260 fast food chains and restaurants. The CalorieKing Calorie Counter for iPhone has a user-friendly interface that allows a quick comparison, of calories, carbs and fat, between foods.

By tapping on a specific food, you can quickly access more detailed information including protein, fiber, saturated fat, trans fat, cholesterol, sodium, and alcohol. Dieting is never easy, but CalorieKing can help by providing the information you need to reach your goal weight and enjoy better health.

Why is this effective? The question in the first line is a great hook. It creates a need and then offers a solution. The addition of claims (“best and reliable”) and assurance (“trusted by health professionals”) tap into the emotional triggers of the target audience (fitness buff, healthy eaters, dieters, etc.).

If you can reverse engineer these descriptions and apply to your own writing, you’ll end up with a great app description.