The API first approach to API development is a strategy where the focus is on designing and developing APIs as the first step in the application development process. This approach prioritizes the creation of robust, scalable, and flexible APIs before the development of the actual application or service that will consume the API. It's a philosophy that treats APIs as the foundational layer of business logic and services, which other applications and services build upon.

How does this differ from design first?

While API First and Design First approaches share similarities in prioritizing API design before coding, there are nuances in their focus and implementation:

- API First is as much (if not more) of a philosophy as it is a development approach. API First considers the API as the organisation's product as opposed to it being considered just a vehicle to serve the organisation's product(s).

It emphasizes the importance of APIs as the primary interface for business logic and services and involves stakeholders from the outset, including not just developers but also business analysts, product managers, and end-users, to ensure the API meets broad business objectives and user needs.

For organisations like Stripe and Twilio, the API is the product and the centre of everything which those organisations are known for. For this reason, good design and documentation drives the success of the business.

- Design First focuses more specifically on the detailed planning and specification of the API's interface before implementation. There is a lot of cross-over in methodology between API First and Design First but the latter is only a methodology and one which could be implemented by the development team alone.

Why Use API First Approach?

1. Cross-functionality and reusability: By focusing on the API up front, you ensure that it is designed to be consumed by a wide range of clients (web, mobile, third-party integrations) which encourages reusability across different parts of the application and even across different projects.

2. Better developer experience (DX): Well-designed APIs make it easier for developers to understand and integrate with the service, leading to faster development cycles and lower integration costs.

3. Enhanced scalability and maintenance: APIs designed first are generally more thought-through, which can result in better scalability and easier maintenance as your application grows.

4. Early feedback loop: Engaging stakeholders early in the API design process allows for gathering feedback and making adjustments before significant resources are committed to development.

Pros

1. Enhanced focus on user and consumer needs: Ensures that API designs are driven by actual user needs and business objectives, not just technical considerations.

2. Facilitates collaboration: Involving stakeholders early and often in the API design process fosters better understanding and collaboration across teams.

3. Improves time to market: Allows parallel development efforts, as frontend and backend teams can work simultaneously, using mock-ups or contracts generated from the API specification.

4. Forward compatibility: Encourages the design of flexible and extensible APIs that can evolve over time without breaking existing clients.

Cons

1. Requires upfront investment: Requires significant effort upfront in planning and designing the API, which can delay the start of actual development.

2. Potential for initial overhead: The need for early consensus among stakeholders and comprehensive API design can introduce initial overhead and slow down the early stages of a project.

3. Risk of misalignment: There's a risk that the API may not fully align with end-user needs if not properly validated, requiring adjustments that could have been avoided with a more iterative approach.

4. Expertise in API design: Demands a high level of expertise in API design principles and practices, which may require training or hiring specialists.

Conclusion

The API first approach is a strategic framework that places the API at the centre of the digital product development lifecycle, ensuring that APIs serve as robust, scalable foundations for applications and services. API First places the API as the product which means that the design and documentation are very much part of the product and it is essential for a company to get these right in order to succeed.