APIs (Application Programming Interfaces)

What are APIs?

APIs (Application Programming Interfaces) are collections of rules and means enabling different software to communicate. Simply put, they’re “agreements for software to safely exchange information.” APIs let developers use public interfaces without knowing internal implementation details.

In a nutshell: Like a restaurant waiter—taking your order to the kitchen and bringing prepared food back. You don’t need to know internal kitchen logic; the role gets fulfilled.

Key points:

• What it does: Safely mediates data and functionality exchange between software
• Why it matters: Efficiently connects multiple services and shortens development time
• Who uses it: Web apps, mobile apps, SaaS, and all software developers

Why it matters

Modern software rarely stands alone. E-commerce connects to payment companies, SNS connects to email services, sales tools link to accounting. Without such integration, user satisfaction stagnates.

APIs enable companies to focus on core functions while combining needed features from other services—the “Microservices” approach. APIs opened new business opportunities. Google Maps API, Twitter API—many companies grew through “API economy.”

How it works

APIs operate through simple request-response flows. Clients ask servers “give me data,” servers reply “here you go.” This back-and-forth is the API.

Specifically, clients send requests to API endpoints (specific URLs). Requests contain “what do you want?” instructions (REST APIs use GET, POST, PUT, DELETE verbs). Servers retrieve database data and return it in predetermined formats (usually JSON). Clients receive responses and display them or use them for next steps.

For example, weather apps ask weather database APIs “what’s Tokyo’s temperature today?” Servers reply “Tokyo: 25°C” as JSON. This exchange happens through authentication (confirming you have rights) safely.

Real-world use cases

Online payments

Clicking “Pay with PayPal” on e-commerce sites triggers the site’s system to tell PayPal API “process this payment amount.” PayPal handles it securely and replies “success.” Sites don’t need PayPal’s internal logic (complex credit card processing).

Login features

“Login with Google” buttons use Google’s authentication API. Sites ask Google “authenticate this email and password,” Google replies “OK, authenticated,” and sites securely implement authentication without complex work.

Real-time data integration

When sales tools and email services integrate via Webhooks (API type), “new customer registered” automatically notifies email services, instantly sending welcome emails. Zero manual work.

Benefits and considerations

APIs’ greatest benefit is development acceleration. Instead of building everything from scratch, combining existing tools delivers new value quickly. SaaS combining multiple services couldn’t exist without APIs.

However, caution is needed. Providers changing API specifications impact users. Weak API security risks data leaks. Poor API key management lets anyone use your account. Trust reliable services, limit permissions to minimums.

Related terms

• REST API — HTTP-method-based API form (GET, POST, etc.), simplest and most widely used
• SaaS — Cloud services like Salesforce and Slack, powered by multiple API integrations
• Microservices — Architecture splitting large systems into small services connected via APIs, highly scalable
• Webhooks — API form where servers automatically “push” data to clients, enabling real-time integration
• Authentication — Process confirming “you have rights to use this service,” underpinning API safety

Frequently asked questions

Q: What are API keys and how should they be handled?

API keys are like passports proving your app uses that service. GitHub, Stripe, OpenAI—most services require keys. Critically: never share keys with others. If exposed, malicious actors can misuse your account. Never hardcode in code; store in environment variables, never commit to Git.

Q: Should I use REST API or GraphQL?

REST API is simple and widely supported—beginner-friendly. GraphQL is flexible, fetching only needed data—better for complex apps. Choose by project scale and complexity.

Q: What are API rate limits?

Providers set limits: “1000 calls per hour.” This protects servers from overload and prevents malicious access. Exceeding limits temporarily blocks calls. Production must respect limits, using caching or batch processing wisely.