API design: a practical guide

The gap between knowing this and actually doing it is where most teams lose ground. This guide covers what API design actually involves, where it usually goes wrong, and how to tell whether yours is in reasonable shape.

The question is rarely whether something can be built, but what it costs to keep running afterwards. Nothing below assumes a large team or a large budget — most of it is a decision somebody has to make and then write down.

Why it matters

Consistent naming saves every future integrator hours. The cost of getting this wrong is rarely visible on the day it happens. Most teams find the first pass takes an afternoon and the maintenance takes minutes a month.

For most businesses the question is not whether this matters but how much of it is worth doing right now. That depends on what you are trying to achieve in the next few months, not on best practice in the abstract. This is the sort of thing that compounds, quietly, in both directions.

How we handle it

Version the API before anyone else depends on it. There is a version of this that is over-engineered, and it is worth avoiding. Assume whoever inherits this will have half your context and none of your patience.

Code gets read far more often than it gets written, and usually by someone with less context than the author had. The version that works in practice is usually less elaborate than the version described in the guides.

Errors should be as well designed as successes. The cost of getting this wrong is rarely visible on the day it happens. If it only works because one person remembers to do something, it does not work yet.

A working checklist

If you want a quick read on where you stand, work through this. Anything you cannot answer confidently is where to start.

• Consistent naming saves every future integrator hours
• Version the API before anyone else depends on it
• Errors should be as well designed as successes
• Someone is named as the owner, not just assumed to be
• There is a date in the calendar to review it again
• The decision and the reasoning behind it are written down somewhere findable
• You could explain the current setup to a new hire in five minutes

Common failure modes

The most common failure is not doing this badly. It is doing it once, during a launch, and never revisiting it. Circumstances move, the setup does not, and the gap widens quietly until something breaks or somebody notices the numbers.

• It was configured during a launch and has not been touched since
• Different people in the business believe different things are true about it
• There is no way to tell whether the last change helped or hurt
• The only person who understands it has left, or is about to

Most development decisions are really maintenance decisions wearing a different hat. That sounds obvious written down. It is still the thing most often skipped.

How we approach it

On our projects this gets handled during the build rather than added afterwards, because retrofitting it costs several times more than including it. We write down what was decided and why, so the next person to touch it is not guessing.

If you are working with someone else, the questions worth asking are simple: who owns this, how will we know it is working, and what happens when it needs to change?

A reasonable first step

Pick the single item from the checklist above that would cause the most trouble if it turned out to be wrong. Fix that one, confirm it worked, then move on. If you want a second opinion on how yours is set up, ask.