API design

Definition

API design is the process of planning and structuring an application programming interface so that it is consistent, reliable, and easy for developers to use. A well-designed API defines how different software components interact, ensuring data and functionality can be accessed securely and efficiently.

Good API design focuses on usability, predictability, and scalability. It defines endpoints, methods, authentication, error handling, and documentation in a way that simplifies integration for developers and supports long-term system growth.

Advanced

At an advanced level, API design involves architectural choices such as REST, GraphQL, or gRPC, depending on performance and flexibility needs. It also includes versioning strategies, rate limiting, caching, and pagination for handling large-scale usage.

Consistency in naming conventions, response formats, and error codes is essential. Advanced API design also prioritises security by implementing encryption, authentication (OAuth 2.0, JWT), and authorisation policies. Tools such as OpenAPI Specification (OAS) or Postman collections are often used to standardise and test APIs.

Why it matters

• Enables smooth integration between systems, apps, and services.
• Improves developer experience and adoption rates.
• Reduces errors and inconsistencies across platforms.
• Supports scalability and long-term system maintenance.

Use cases

• Designing public APIs for third-party developers.
• Building internal APIs for microservices communication.
• Creating APIs for mobile apps to connect with backend systems.
• Standardising data access for enterprise platforms.

Metrics

• Developer adoption and satisfaction scores.
• API response time and error rates.
• Number of successful calls versus failed calls.
• Documentation completeness and usability.

Issues

• Poorly designed APIs cause integration challenges.
• Inconsistent responses create confusion for developers.
• Lack of versioning breaks existing applications when updates occur.
• Weak security in API design can expose sensitive data.

Example

A payment company designs a REST API with clear endpoints, consistent JSON responses, and strong authentication. Developers easily integrate payment processing into e-commerce platforms, increasing adoption. The company tracks response times and uptime, maintaining reliability and trust with partners.