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The Principles of API Design

Outlines the main elements of API design, how it fits in with software design, and which elements produce effective Web API design.
This chapter is from the book

All architecture is design, but not all design is architecture. Architecture represents the set of significant design decisions that shape the form and the function of a system.

— Grady Booch

Organizations have been delivering APIs for decades. APIs started as libraries and components shared across an organization and sold by third parties. They then grew into distributed components using standards such as CORBA for distributed object integration and SOAP for integrating distributed services across organizations. These standards were designed for interoperability but lacked the elements of effective design, often requiring months of effort to successfully integrate them.

As these standards were replaced by Web APIs, only a few APIs were needed. Teams could take the time to properly design them, iterating as needed. This is no longer the case. Organizations deliver more APIs and at greater velocity than ever before. The reach of Web APIs goes beyond a few internal systems and partners.

Today’s Web-based APIs connect organizations to their customers, partners, and workforce using the standards of the Web. Hundreds of libraries and frameworks exist to make it cheap and fast to deliver APIs to a marketplace or for internal use. Continuous integration and continuous delivery (CI/CD) tools make it easier than ever to build automation pipelines to ensure APIs are delivered with speed and efficiency.

Yet, the biggest challenge for today’s API programs continues to be successfully designing APIs that can be understood and integrated by developers in a consistent and scalable fashion. Facing this challenge requires organizations to recognize that Web APIs are more than just technology. Just as works of art require the balance of color and light, API design benefits from the blending of business capabilities, product thinking, and a focus on developer experience.

The Elements of Web API Design

An organization’s collection of APIs provides a view into what the business values in the marketplace. The design quality of its APIs provides a view into how the business values developers. Everything an API offers—and doesn’t offer—speaks volumes about what an organization cares most about. Effective Web API design incorporates three important elements: business capabilities, product thinking, and developer experience.

Business Capabilities

Business capabilities describe the enablers an organization brings to market. They may include external-facing capabilities, such as unique product design, amazing customer service, or optimized product delivery. They may also include internally facing capabilities such as sales pipeline management or credit risk assessment.

Organizations deliver business capabilities in three ways: directly by the organization, outsourced via a third-party provider, or through a combination of organizational and third-party processes.

For example, a local coffee shop may choose to sell custom coffee blends. To do so, it sources coffee beans through a third-party distributor, roasts the coffee beans in-house, then utilizes a third-party point-of-sale (POS) system for selling its coffee blends in a retail store. By outsourcing some of the necessary business capabilities to specialized third parties, the coffee shop is able to focus on delivering specific business capabilities that differentiate them from others in the marketplace.

APIs digitize the business capabilities that an organization brings to a marketplace. When embarking on designing a new API or expanding an existing API, the underlying business capabilities should be well understood and reflected into the API design.

Product Thinking

Organizations were integrating with partners and customers prior to the growth of Web APIs. The challenge most organizations face, however, is that each integration has been custom made. For each new partner or customer integration, a dedicated team consisting of developers, a project manager, and an account manager were tasked with building a custom integration. This involved tremendous effort and was often repeated, with per-partner customizations.

The growth of the software-as-a-service (SaaS) business model, along with the increase in demand for Web APIs, have shifted the discussion from one-off integration with partners and customers to a focus on product thinking.

Applying product thinking to the API design process shifts the team focus from a single customer or partner to an effective API design that is able to handle new automation opportunities with little to no customization effort for a given customer segment. It also enables a self-service model for workforce, business-to-business, and customer-driven integration.

The focus of an API product becomes less on custom implementations and more on meeting market needs in a scalable and cost-effective way. Reusable APIs emerge from considering multiple consumers at once. When embarking on the design of a new API, use a product thinking approach to obtain feedback from multiple parties that will consume the API. Doing so will shape the API design early and lead to increased opportunities for reuse.

Developer Experience

User experience (UX) is the discipline of meeting the exact needs of users, from their interactions with the company to their interactions with its services and with the product itself. Developer experience (DX) is just as important for APIs as UX is for products and services. The DX focuses on the various aspects of engagement with developers for an API product. It extends beyond the operational details of the API. It also includes all aspects of the API product, from first impressions to day-to-day usage and support.

A great DX is essential to the success of an API. When a great DX is delivered, developers quickly and confidently consume a Web API. It also improves the market traction of productized APIs by moving developers from being integrators to becoming experts on the API. The expertise translates directly into the ability to deliver real value to their customers and their business quickly and with reduced effort.

As API teams seek to understand how to design a great experience for their API, remember that DX is an important factor for internal developers, also. For example, great documentation enables internal developers to understand and consume an API quickly, whereas an API that has poor documentation requires contacting the internal team responsible for the API to learn how to use it properly. While they may be able to gain direct access to the developers that designed and implemented an API, it adds unnecessary communication overhead. Internal developers benefit from great DX because they can create business value faster.

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