Our API Guidelines can be summarized as follows: Be Nice.  If you’re smart enough to write code that uses our API, you’re smart enough to know what we mean by that.

OK, if you really want us to spell it out, here are some specifics:

1. Don’t spam. And by this we don’t just mean to make sure you’re compliant with the Can-SPAM Act.  We mean: don’t do anything that’s perceived by our users as spam, whether or not it can technically be considered spam.  Don’t blast questions to users, or otherwise do something that annoys people.
2. Don’t trick users. Your application should make it clear to users how it works with their their formspring.me account and data.  They shouldn’t authenticate your application then unexpectedly send questions to people they didn’t expect to, suddenly see questions in their Inbox disappear, or see content appended to questions that they didn’t write.
3. Don’t crash our servers. We have rate-limits in place for a reason, so don’t try to get sneaky and work around them for whatever reason.  If you have legitimate needs for making requests more frequently than our limits allow, please talk to us and we’ll try to accommodate you if we can.  Cache heavily, and be conscious of the fact that nice people have to wake up at 4am on a Saturday morning when you fry our servers.
4. Don’t misuse our trademark. We want to prevent any potential confusion that can come from the use of “formspring” in 3rd party sites and applications. Feel free to use language on your site or within your application that talks about how it’s built on the formspring.me platform so users understand what it’s for and what it can do. However, you shouldn’t use “formspring” in the name of your site or application. You also shouldn’t register a domain or apply for a trademark containing “formspring” or a variation thereof. It’s OK to use the words “form” and “spring” individually though.

This isn’t everything, but it’s a pretty good start.  Questions are welcome: http://www.formspring.me/api

Thanks!