What is an API?

An Application Programming Interface, or API, serves as a set of defined rules that explain how computers or applications communicate with one another. It acts as an intermediary layer that processes data transfers between systems.

At its core, an API allows one piece of software to access the features or data of another piece of software. It does this without requiring the developer to understand the internal code or database structure of the external system.

For a founder, this is the difference between building a bank from scratch and simply plugging into a payment processor. It is a tool for leverage.

To visualize this, imagine sitting in a restaurant. You are the user. The kitchen is the system or server that creates the value (the food). You cannot simply walk into the kitchen and start grabbing ingredients. You need an interface to communicate what you want.

In this scenario, the waiter is the API.

1. You give the waiter your order (the request).
2. The waiter takes the order to the kitchen.
3. The kitchen prepares the food based on strict guidelines.
4. The waiter brings the food back to your table (the response).

The waiter shields you from the chaos of the kitchen. You do not need to know how the stove is calibrated or who chopped the onions. You only care about the result. An API functions exactly the same way for software.

Speed is often the only advantage a startup has over an incumbent. APIs are critical for maintaining that speed.

Instead of engineering complex systems, you utilize existing services. If you need to send transactional emails, you use the SendGrid API. If you need search functionality, you might use the Algolia API.

This approach allows your engineering team to focus on your core competency. It prevents you from reinventing the wheel for problems that have already been solved by other companies.

However, it also requires you to design your own internal APIs. As your application grows, you may want to separate your mobile app from your web app. Both of them will need to talk to your central database. Building an internal API allows both your iPhone app and your website to request the same data from the same source efficiently.

It is helpful to distinguish the API from the UI.

A User Interface (UI) is designed for humans. It prioritizes visual hierarchy, colors, and ease of use. It handles clicks and taps.

An API is a user interface for machines. It prioritizes logic, structure, and speed. It handles data requests and logic flows.

When a user clicks a button on a beautiful UI, the background process often triggers an API call to fetch the necessary information to show the user what they asked for.

Using APIs creates dependencies. This is a concept every founder must weigh carefully. When you build on top of an API, you are renting functionality rather than owning it.

If the API provider raises their prices, your margins compress. If they change their documentation or shut down access, your product breaks.

We must ask ourselves difficult questions during the build phase.

Is this function core to our business survival? If the answer is yes, relying entirely on a third party API introduces significant risk. If the answer is no, then offloading that work to an API is likely the correct business decision.

Understanding where the line is drawn between proprietary tech and integrated tech is a fundamental responsibility of the founder.