I recently transitioned off the API team and moved work on web client team at work. I wanted to share some things I wish I had known when I was deepdiving in developing REST API.

1. Stability uber alles

You can drop nearly everything on the ground and focus on restoring stability of the API. No one will mind.

2. Versioned API from the start

APIs are suppose to return consistent data that’s been agreed by the server and the client. There are times when the server must change the response body structure to serve the needs of some clients better. You should not change the response structure for a given endpoint in such case. You should version your API so that you can serve the needs of the old clients and new clients equally well.

Versioning can easily be a topic of conversation on its own, but here are several considerations you need to make when you implement versioning.

  • Where is versioning going to occur? At load balancer or at app?
  • Is it going to be done via header or url?
  • How are you going to isolate the code change to remain within a specific version? Also while ensuring that the versioning doesn’t make coding any more difficult.
  • How will you automatically test the newly versioned APIs?

3. Use API specs

Make use of spec to come to an agreement between you and the clients before building the API. You will be able to serve their needs better and also possibly explain to the clients your limitations.

4. Load testing

I didn’t realize how important this is until our production environment was adversely affected by some feature changes we made without properly load testing them first. Develop a load testing strategy for your codebase and be ready to reject code changes that could affect production environment negatively.

5. Leverage your teammates and clients for advice

Compared to other kind of products I used to work on developers usually have more correct opinions about building API.