API Specification

An API Specification is a document or set of documents that describes the features, operations, inputs, and outputs of an API (Application Programming Interface). It acts as a contract between the API provider and the consumer, ensuring both parties agree on how the API behaves.

Purpose

Defining an API specification enables separation of concerns between the API provider and consumer, allowing each to focus on their respective responsibilities because of the consistency and reliability it provides.

• Consistency: Standardised services ensure consistent and predictable interactions.
• Efficiency: Minimises the overhead of collaboration by providing clear expectations and requirements upfront.
• Independence: Allows teams to work independently while ensuring interoperability.

Format

API specifications can be defined in various formats, including:

• OpenAPI Specification (OAS): A widely used format for describing RESTful APIs.
• GraphQL Schemas: For APIs using GraphQL, detailing types, queries, and mutations.
• gRPC Protocol Buffers: For gRPC services, using Protocol Buffers to define service methods and message types.

Anti-patterns

• Tightly Coupled Design: Making the API too specific to a particular client implementation.
• Lack of Versioning: Not incorporating version control into API contracts can lead to compatibility issues.
• Insufficient Testing: Failing to thoroughly test API integrations against the contract can result in undetected issues and integration failures.
• Poor Documentation: Inadequate or outdated contract documentation can cause confusion and misalignment between teams.