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When I started to design Matomo (Piwik) I read a lot about APIs, software architecture, service oriented architecture (soa), etc. I really wanted to design a modular architecture that would make it easy to request any data and perform any action from outside the user interface.

Technically speaking, Matomo has been built on the top of Apis. Everything that does some logic in Matomo is available through an API. We basically open all these APIs via a REST API. Of course you must authenticate for some calls eg. when deleting a user. In the user interface, AJAX requests are directed to the API module that returns data in HTML or JSON format (javascript friendly).

Here are the main concepts I tried to apply when designing the API:

• Easy to learn ; the documentation provides simple examples, complete documentation
• Easy to use ; single entry point, standard parameters
• Hard to misuse ; explicit error message suggesting parameters values
• Appropriate to audience ; I talked about such a service with several users, and looked at what the competition was offering

Interesting resources that helped me have a better understanding of the topic:

• How to design a good API and why it matters? Great PDF presentation by a google engineer that I really enjoyed
• How to add an API to your webservice? Interesting read
• Audience drived based API design
• The art of building a reusable class library. A great presentation by a microsoft engineer ; be ready for the 237 slides!! (that’s a reason you end up working for microsoft when you like powerpoint so much!)

Updated September 2014 – six years after writing this article it is good to see how popular and useful APIs have become! Nowadays it’s all about RESTful Json APIs.

If you like watching videos this is a good one: REST+JSON API Design – Best Practices for Developers (video). We hope to release our JSON RESTful API for Matomo 3.0

End update

Of course, to design a good API you should take a look at existing APIs, and even use some of them:

• A great example: Flickr API ; see an example of a method documentation ; try the API explorer for this method
• Mediawiki API
• A more complex example: Ebay API ; see an example of a method documentation (yes it’s impressive!!)
• A directory of existing APIs on programmable web
• Amazon API: example of the method ItemSearch
• And last but not least the Matomo API ; the best web analytics API that makes it easy to request anything from your best keywords, your top pages or the number of visits of the last 30 days, yesterday, or the previous 5 months. Give it a try with this tutorial.

If you have good resources or advice, feel free to post a comment. Good luck designing your API!