API Development and Integration: A Practical Guide

Key takeaways

• An API is a defined way for two systems to share data and trigger actions.
• You need an integration when people copy data between tools by hand.
• REST suits most cases; GraphQL helps when clients need flexible queries.
• Protect every API with authentication, scoping, rate limits and validation.

Most businesses run several systems that should share data but do not. The store knows the orders, the ERP knows the stock, an app knows the customers, and a person spends the day copying figures between them. An API ends that copying by letting the systems talk to each other directly.

What an API is

An API is a defined way for one system to ask another for data or to send it data. Instead of a human reading a screen and typing into another tool, a request goes out, and a clean answer comes back in a predictable format, usually JSON. The two systems agree on what can be asked and what the answer looks like, so the exchange is reliable.

When you need an integration

You need an integration when related data lives in two places and people move it by hand. The signs are familiar:

• The same record is entered twice, in two systems.
• Numbers do not match across your tools.
• Reports are built from exports stitched together.
• Partners ask for data by email, and you fill it in by hand.

REST and GraphQL

Both are standards for building APIs. REST exposes resources at clear paths, is simple and widely supported, and suits most integrations. GraphQL lets a client ask for exactly the fields it needs in one request, which helps apps that pull a lot of related data. Neither is better in the abstract. Pick the one that fits the systems and the way the data is used. We cover the choice in more detail in our REST and GraphQL guide.

Keeping an API safe

An API exposes your data, so it has to be secured properly from the start:

• Authenticate every caller with API keys or OAuth.
• Scope access, so each caller only reaches its own data.
• Rate limit, so no caller can overload the system.
• Validate every request, and keep the ability to revoke access.

How to build one that lasts

• Map the data in each system before you design endpoints.
• Plan versioning, so future changes do not break callers.
• Use webhooks for events, so callers are told instead of polling.
• Document it, so your team and your partners can use it without asking.

Done this way, an API stops the manual copying, keeps your systems in agreement, and gives partners and apps a clean way to connect.