Building a RESTful API like a Product Manager

Something I have been thinking about for a while is the idea of APIs as your Product - the idea that you should design, build and test your API like it's a public facing product (as it might actually be if its a public API), and what lessons we should be learning from Product Managers about how we achieve this.

In the latest instalment of their "Technology Radar", ThoughtWorks recommended the concept "API as a Product" as ready to trial (although I think it's far beyond trial stage - I can see no real risk of adopting the lessons from Product Management for your API).



I have generally been interested in Product Management for several years - I think it's hard not to get interested in the science of Product Management when you are building side projects, as you naturally have to think about the product you are building - sure, with side projects they can easily turn into vanity projects, where you just build what you think is cool, but I think it's still fun to think about real users and good Product Management techniques that can be applied even to side-projects.

Having tried to gain some understanding, I have turned to some classic material on the subject of Product Management: The Lean Startup, Don't Make Me Think, How to Build a Billion Dollar App. I have also been lucky enough to attend Mind The Product Conference twice (though volunteering - but managed to watch lots of the talks), and to have worked with several great Product Managers.

So what lessons can we start applying? I think, if one statement sums it up, its an idea from Kathy Sierra:

Does your product make your users awesome?

This is a great way to think about APIs (I'm mostly talking about REST/GraphQL type APIs here - but this thinking is a great way of approaching design for normal class/interface/library APIs too).

As engineers, I'm sure we have all used APIs that don't achieve this - APIs that make us have to think, that make us feel stupid, that seem overly complicated (for example, the old Java Date library - the number of times I had to google just to find out how to simply create a specific date for something simple like a unit test is ridiculous). And hopefully, we have all used APIs that make us feel awesome - APIs that make us productive, that let us do what we expect to be able to do, and can (with the help of the IDE's auto-complete) let us guess what the method calls are.

Another idea Kathy Sierra mentions in that talk, and is also made famous from the title of the Product Management classic, is:

Don't make me think

I have written before about the StackOverflow and GitHub APIs, but they deserve a mention again, if you have ever written an integration with them, you will know.  The APIs are designed in such a way that sensibly models the domain model.

For example, take StackOverflow, if we were going to describe their domain model, what first class objects would we have? I guess Questions, Answers, Comments etc - and sure enough, their API models these:

/questions - will get you all the questions on the site

/answers - will get you all the answers,

Now, how do you think you might get all answers for a given question? Well, a list of answers should probably be a child of a question, so something that represents that, something like:

/questions/{Question ID}/answers

Sure enough, thats the URL - and the behaviour is consistent through the design, I'm sure you can guess how you might retrieve all comments for a given answer.

I'll be honest, developing against an API where I can guess the endpoints makes me feel pretty awesome.

MVP and the Lean Product

The idea of a Minimum Viable Product is a core concept in Lean Startup - the idea that you build the minimum version of the product that can get you feedback as to whether you are heading in the right direction before investing more effort in building out a fuller fledged product.

Whilst I think an appreciation of an MVP is a good awareness for any engineer - I have generally found it is useful in facilitating conversation when building a new product - if as an engineer you recognise some new feature is going to be considerable effort, its helpful to think about what hypothesis the feature is trying to test, and is there a simpler engineering solution to test the hypothesis.

However, the principal of not over engineering the API is also a good one - once you have a well designed domain model, its quite tempting to get carried away with REST design best practices and start building endpoints for all different variations of the model - however, unless you need them, it's better to start with less (if you are building a public REST API from the start then it might be harder to know what isn't needed, but you can still certainly build an MVP version of the API to test the hypothesis - e.g. whether people actually want to use your API)

User Testing

Another important part of building a product is collecting user feedback - Whilst a REST API may not be well suited to A/B testing (your consumers won't be very happy if switch the API design on them after they have implemented against a specific variation!), listening to user feedback is still important - because the consumers will likely be engineers (writing the client code), then hopefully they will be expecting REST standards and good API design principles, but another way to think about this is the importance of not making breaking changes to your API.

A technical way of thinking about this is Consumer Driven Contracts Testing - As RESTful APIs are de-coupled from the client code, the API doesn't have any idea what clients are using or doing, so this approach allows consumers to define what they expect from the API, and then the API can always test against these contracts, so be sure that any change to the API is still in keeping with existing consumers, or users, of the API.

Conclusion

I think, in general, all engineers can benefit from thinking about how good products are built, what concepts are important, and be able to think about the products or services they are building in this way - both in terms of thinking about the actual implementation as a product that someone else will be the user of (either externally if a RESTful API, but also internally if its cross-team or even just someone coming to take over your code once you have moved on).