What is API-First Development?

API-first development is a new way of making software. It means making the parts that let different programs talk to each other first before creating the rest.

API-first development is a big deal for both businesses and developers. Focusing on APIs early on in the process is important because:

• Streamline Development: APIs are reusable components for time and resource management. For example, APIs are compared to building blocks that can be used repeatedly.
• Boost flexibility:  API-first architecture includes modularity. 
• Foster Collaboration: API definitions serve as a contract among developers.
• Drive Innovation: APIs build partnerships and integration. For example, Twilio offers APIs for making calls, sending messages, and taking videos in the cloud.

Here are the advantages of an API-first approach: 

• Fasten Time-to-Market: This entails speeding up the development process.
• Increase Scale: This includes increasing parts of your app as preferred.
• Improve Maintainability: This focuses on the update and management of the app in separate parts.
• Developer Experience: The requirement of clarity in API documentation and implementation of clear protocols make the integration process more cohesive.

The OpenAPI Specification (OAS), was previously called Swagger. It is a common standard for explaining RESTful APIs. This includes a machine-readable way to define API endpoints, request and response formats, authentication methods, and more.

OAS in an API-first approach has the following advantages:

• Standardized Documentation:  OAS ensures consistent API documentation.
• Automated Code Generation: OAS has automated code generation.
• Simplified Testing: OAS creates and executes API tests.

Microservices can be described as several small self-contained pieces that together provide the functionalities of an application, similar to an assemblage of a puzzle.

This means they have to communicate with each other to run the process smoothly. Well, as it turns out, this is where APIs fit in the picture. 

The API-first approach entails the design of communication channels. API-first and microservices go hand in hand as both are concerned with the concept of product-linking design within the context of an application.