Glossary
What is API (Application Programming Interface)?
A defined way for one piece of software to ask another for information or actions, such as a mobile app talking to a server.
In plain words
An API is a set of rules that lets two programs talk to each other. When a weather app shows today's forecast, it sends a request to a weather service's API and gets the data back. A restaurant analogy works: the menu lists what you may order, and the kitchen does the work, so you never need to enter the kitchen.
Why they matter when hiring a developer
- Your mobile app and your website can share one back end
- You can connect payments, maps, messaging and accounting without building them
- Other companies can connect to your product, which can become a feature of its own
- A well-designed API makes later changes cheaper
What a good API has
- Clear written documentation that matches how it really behaves
- Authentication, so only permitted users and systems can use it
- Limits on how often it can be called, to prevent abuse
- Versions, so a change does not break users of the old one
- Helpful error messages and logging
Common mistakes
- No documentation, so only the original developer understands it
- Weak or missing authentication
- Changing it without warning and breaking apps that depend on it
- Returning more personal data than the caller needs
Questions to ask a company that offers this
- How will the API be documented, and will we own the documentation?
- How is access controlled and limited?
- How will you version it so changes do not break existing users?
- How do you test it?
- What happens if a service we depend on goes down?
A good company will answer these plainly and in writing. Vague or evasive answers are worth noting.
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Explanation last read through on 13 October 2026. It is general guidance in plain language, not advice for your particular project. Tell us if something is wrong or unclear.