What is API Design?

API design makes deliberate choices about how an API will present data and functionality to its users. Effective API design outlines the API’s endpoints, methods, and resources using a standardised specification format.

The design process works for users and developers. Why? It ensures APIs meet business goals while being user-friendly, adaptable, testable, and well-documented. API design should be addressed early in the API lifecycle to ensure alignment among key stakeholders and to identify potential issues before they become entrenched. It also plays a crucial role in API governance by helping teams create standardised API patterns that can be reused within the organisation.

In this blog, we’ll look at the key stages of API, REST API, and some of the different types of API available.

What are the key stages of API design?

Every organisation should follow some fundamental steps when designing an API. These steps require teamwork among stakeholders, including business leaders, developers, consumers, and partners, to ensure the API meets everyone’s needs. Collaborating throughout the process also helps developers avoid adding unnecessary features. 

Here are the steps for API design:

1. Define the API’s purpose

The first step is to reach a consensus on what the API is supposed to accomplish. Different APIs serve different functions; for example, an API for authentication has different requirements than one for browsing a product catalogue. Understanding the use case is crucial before making other decisions. The use case will also influence the architecture choice, such as using gRPC for internal microservices or GraphQL for integrating multiple data sources. Once the API’s purpose is clear, stakeholders should describe how the API will fulfil specific needs in plain language.

2. Ensure Reliable Service Contracts for APIs

When running one or more services, it’s crucial to have dependable service contracts that define their APIs. These contracts usually consist of detailed interface definitions that precisely outline and type the API each service offers. This makes it essential for the service code to accurately implement the interface, ensuring it meets its contract obligations. Detecting regressions and communicating changes through updates to the contract is vital. 

Service contracts typically include the following components:

• The endpoints available and the operations each endpoint supports
• Input and output parameters for each operation
• Authentication methods
• Contact information, licence, terms of use, and other relevant details

3. Validate with mocks and tests

With the API definition ready, you can create mock servers that simulate the API’s behaviour. Mock servers return sample data in response to requests, allowing you to verify that the API is functioning as expected. You can also run tests manually, on a schedule, or automatically through CI/CD pipelines. Mocking and testing during design help identify and fix issues early, preventing consumer codebase problems.

4. Document the API

The final step is to document the API thoroughly. This involves detailing every resource, method, parameter, and path to ensure users can use the API quickly. Documentation should include examples of requests and responses to help users understand how the API supports common business needs. Some tools can generate documentation automatically from the API definition, keeping it up-to-date without extra effort from the team.

Different types of APIs

There are four APIs in mainstream web services: partner, public, private and composite. 

Here, we’ll go into each type of API in more detail…

Partner APIs

Partner APIs streamline B2B interactions by providing access solely to authorised external developers. Imagine a company needing to share customer data with external CRM systems; a partner API links the internal data to those CRM firms, ensuring no other API use.

Public APIs

Public APIs, also known as open or external APIs, are open to any developer or business. Companies that want to share their applications and data create public APIs. They usually require moderate authentication and may be monetised on a per-call basis.

Internal APIs

Internal APIs, or private APIs, are designed for companies to integrate their systems and data –for example, linking payroll and HR systems. Traditionally, internal APIs had weak or no security measures, but rising security threats and compliance demands are changing this approach.

Composite APIs

Composite APIs merge multiple APIs to perform a series of related tasks. They are useful for handling complex API operations and can enhance performance and speed compared to using individual APIs separately.

What is a REST API?

A REST API, or RESTful API, is a type of web API that adheres to the principles of the REST architectural style and enables interactions with RESTful web services. The acronym REST stands for representational state transfer.

REST defines a set of architectural principles rather than a specific protocol or standard, allowing developers to implement it differently. When a client makes a request through RESTful API, it receives a representation of the resource’s state. This data can be presented in various formats through HTTP, such as JSON (JavaScript Object Notation), HTML, XML, Python, PHP, or plain text. JSON is particularly popular due to its language-agnostic nature and human and machine readability.

Additionally, headers and parameters are crucial in HTTP methods used in RESTful API requests. They provide essential information about the request’s metadata, authorisation, uniform resource identifier (URI), cookies, caching, and more. There are distinct headers for requests and responses, each carrying HTTP connection details and status codes.

Features of a well-crafted API

The advantages of a well-crafted API include enhanced developer experience, quicker documentation, and increased adoption for your API. But what exactly constitutes good API design? 

Generally, an effective API design will exhibit the following features:

• Easy to understand and use: A well-crafted API will be user-friendly, with resources and operations that can be quickly grasped by developers who interact with it regularly.
• Difficult to misuse: Implementing and integrating with a well-designed API will be straightforward, reducing the likelihood of writing incorrect code. It provides informative feedback and does not impose overly strict guidelines on the API’s users.
• Comprehensive and succinct: A comprehensive API will enable developers to create full-fledged applications with your data. Achieving completeness typically occurs over time, with API designers and developers gradually enhancing existing APIs. This is an ideal goal that every engineer or company with an API should aspire to reach.

Kick Off Your API Design with Mulesoft

MuleSoft is a single web interface with a comprehensive toolset to help you manage APIs and integrations. Its wide functionality, from implementation to analysis and SLA monitoring, helps simplify and accelerate your connectivity. Plus, MuleSoft Automation helps boost productivity by connecting apps and automating processes. Learn more about getting started with automation and implementation with our Salesforce Integration Customer 360 ebook.