The much-awaited Application Programming Interface (API) for movie site Netflix will launch tomorrow, according to an email from the company. As HackingNetflix found out last week, the launch event will occur at the AJAX Experience conference. Details are listed below. It looks pretty good, but there are some major limitations, too.

Millions of people love movies via Netflix, making this API an opportunity for all kinds of developers to add well-known value to any other application.

The company says the API will allow access to data for 100,000 movie and TV episode titles on DVD as well as Netflix account access on a user's behalf.

Presumably this does not mean that 3rd party applications will be able to pull in the streaming content available on the Netflix site, but rather that they'll be able to make user data portable for offering personalized content on their applications based on a user's Netflix activities. Users will still have to visit the Netflix site itself or to one of the big integration partners like LG or Xbox in order to watch streams. Last week Netflix cut deals with the Disney Channel and CBS to put nearly 100 of their shows on the Netflix site. You vibrating hamster Facebook app will not be able to show your users their favorite Netflix video inside the hamster, though, you just get to interact with their list of favorites content as data.

Update: Now that the API is live, we see that our assumption here was wrong. As reader Dave Jeyes points out in comments, the documentation includes code for a play button and a media player. Cool!

It also appears that this is a read-only API, meaning that movies cannot be requested or other account information changed, from inside of 3rd party applications. We presume there will be affiliate links made available so that users can click through and developers can make some profit.

Update: It turns out our hunch was wrong about read-only. In an email response to the question, the company says: "Write capabilities: yes. We wanted to enable full movie queue management, so there are write capabilities in that a user can add movies to their queue, reorder their queue, and remove movies. Ratings can also be written, i.e. a user can rate a movie using the API."

Speaking of developer profit, commercial use of the API will be accepted. Netflix says, for example, that developers can sell an app in the iPhone app store that uses the Netflix API. That's great, there are far too many commercially desirable APIs around the web for which commercial use is prohibited.

The API includes access to data via REST API, a Javascript API, and ATOM feeds. No JSON, which we suspect will disappoint some developers.

User authentication will occur using OAuth, the open standard we and others have been cheering for and the protocol now used for all the Google Data APIs.

So the good news is that Netflix is using standards based authentication, making it very easy to develop against, is allowing commercial use and is finally launching the interface. The bad news appears to be that it's user-data only and appears to be read only. We'll update this post if we get any more details from the company before launch tomorrow. Update:Now that we've seen more information about the API, it appears that there is no bad news. This is great stuff.

The API will be available at http://developer.netflix.com by self sign-up tomorrow. That site is currently password protected.