5 Best Practices for Building Exceptional APIs in 2023

APIs are everywhere. As of 2023, over 90% of developers use APIs in their applications, and 98% of Fortune 500 companies leverage APIs for critical business functions. With over 26,000 public APIs available and billions of API calls made every day, it‘s clear that APIs are the backbone of modern software.

However, not all APIs are created equal. Poorly designed APIs can lead to frustration for developers, unreliable applications, and even security breaches. That‘s why following API development best practices is crucial for building high-quality, successful APIs that stand the test of time.

In this in-depth guide, we‘ll dive into five essential best practices that every developer and organization should adopt for their API projects in 2023. These practices are based on hard-earned lessons from API experts, official standards, and my own decade of experience in API design and development.

Whether you‘re building your first API or looking to level up your API game, this advice will help you create exceptional APIs that are secure, reliable, easy to use, and built to last. Let‘s jump in!

1. Design API-First, Not Code-First

The first and most important practice is to adopt an "API-first" mindset. As Tyk explains it:

"API-first means that for any given development project, your APIs are treated as ‘first-class citizens.‘ That everything about a project revolves around the idea that the end product will be consumed by mobile devices, and that APIs will be consumed by client applications and third-party developers."

In other words, API-first means you design the API contract first before writing any code. You work with stakeholders to define the API‘s functionality, endpoints, request/response schema, and security model. Then you capture all of this in a machine-readable API definition using a spec like OpenAPI.

Only after the API contract is defined and agreed upon do you begin implementing the API server and client code to match the spec. The API definition becomes the central source of truth that keeps everyone in sync.

This is the opposite of the old "code-first" approach where APIs were an afterthought tacked on to an existing codebase. Code-first APIs tend to expose internal implementation details and be inconsistent.

API-first offers key benefits like:

• Improved communication between stakeholders
• Ability to parallelize API development
• Automatically generate documentation, SDKs, and tests
• Catch design issues early before code is written
• Ensure APIs aren‘t biased toward specific implementations
• Encourage consistency and reuse across APIs

In fact, APIs developed with API-first are 4-5 times less likely to have issues compared to code-first APIs.

For example, Stripe is well-known for their API-first approach:

"The Stripe API is specified in a master OpenAPI description document. This document is used to generate documentation, SDKs, mock servers, and some integration tests. We treat the API definition as code, reviewing all changes and tracking issues on our API just like the rest of our codebase."

To get started with API-first, check out open source tools like:

Tool	Use
Swagger Editor	Design OpenAPI specs
Apibldr	Visually model APIs
Apicurio	Design APIs collaboratively
Stoplight	Manage API design lifecycle

By defining your API contract first with machine-readable specs, you‘ll build more consistent, interoperable, and future-proof APIs.

2. Secure APIs With Multiple Defense Layers

Security is non-negotiable for APIs. Gartner predicts that by 2024, API abuses will be the most frequent attack vector for enterprise web applications.

We‘ve already seen major companies like Facebook, Venmo, and Panera Bread suffer API breaches that exposed millions of user records. Poor API security puts your users‘ data and your company‘s reputation at risk.

API security requires a layered defense approach that addresses risks at multiple levels:

1. Network level – Use TLS encryption for all API calls, even internally. Require APIs to be accessed through a trusted API gateway instead of direct network access. Implement rate limiting and throttling to prevent denial-of-service attacks.

2. Application level – Follow the principle of least privilege when designing API access control. Use short-lived OAuth tokens instead of long-term API keys. Validate and sanitize all incoming data to prevent injection attacks. Don‘t expose sensitive data or system internals in API responses.

3. Code level – Follow secure coding practices to avoid introducing vulnerabilities like cross-site scripting and SQL injection. Keep dependencies up-to-date and scan for vulnerabilities. Perform static and dynamic security testing.

4. Operational level – Monitor API traffic for anomalies and suspicious activities. Use AI to analyze API payload contents. Have an incident response plan for API breaches. Encrypt API secrets in transit and at rest.

For example, Twitter requires all API calls to use HTTPS, OAuth 2.0 for authentication, and scopes to limit permissions. They also offer a bug bounty program to reward security researchers.

Recommended API security standards and tools:

Tool	Use
OpenID Connect	API authentication framework
OWASP API Security Top 10	Top API security risks and how to address them
42Crunch	Continuous API security auditing platform
APIsec	AI-powered runtime API protection

While no API is 100% immune from threats, implementing multiple layers of defense will make your APIs significantly harder to exploit.

3. Make Your APIs Developer-Friendly

Great APIs put the developer experience first. After all, an API that is hard to learn and use will struggle to gain adoption, no matter how powerful it may be.

As Twilio puts it:

"APIs that are designed for developer usability are taking a key step towards differentiation from their competitors. An API with strong usability allows developers to on-board faster, integrate more quickly, and ultimately, will win more market share from their target users."

Here are some key principles for designing developer-friendly APIs:

• Use intuitive, consistent naming conventions for endpoints and parameters
• Provide clear, human-readable error messages with helpful tips
• Support "progressive enhancement" by offering sensible defaults
• Return resource links in responses to enable HATEOAS
• Version your APIs to avoid breaking changes for clients
• Offer SDKs and code samples in popular languages
• Dogfood your own APIs internally to understand pain points
• Gather feedback from your API community and act on it

Most importantly, provide excellent documentation! Your API docs should be the go-to resource for learning how to use your API. Stripe and Twilio are often cited as gold standards for API documentation.

Great docs should include:

• Getting started tutorials and quick start guides
• Full API reference with auth, endpoints, parameters, requests/responses
• Code snippets and sample apps in multiple languages
• Best practices and gotchas to avoid
• Change logs and migration guides
• Community resources like forums and chatrooms

Consider using documentation tools like:

Tool	Use
GitBook	Collaborate on API documentation
ReadMe	Beautiful API reference docs
Postman	Auto-generate docs from collections
Slate	Create elegant API docs with Markdown

Remember, empathy is key. Put yourself in the shoes of a new developer trying to use your API for the first time. What questions would they have? What might trip them up?

The easier you can make your API to adopt, the faster it will grow!

4. Test Continuously With Automation

Like any software, APIs need rigorous testing to ensure quality and prevent regressions. Manual testing is time-consuming, error-prone, and impossible to scale.

That‘s why continuous automated testing is a critical best practice for APIs. With automated tests, you can check your API‘s functionality, reliability, performance, and security with every code change.

Spotify uses a variety of automated API tests:

"When it comes to API testing, we classify them into 4 different categories: unit tests, integration tests, contract tests and end-to-end tests…We want to catch bugs as early as possible."

Some key API testing practices:

• Write API unit tests that stub out dependencies and check boundary cases
• Create integration tests that check API workflows and dataflows
• Use contract testing to verify APIs and clients match the API spec
• Perform fuzz testing to throw random data at APIs
• Load test APIs to measure performance at scale
• Continuously scan for API security vulnerabilities

Popular API testing tools include:

Tool	Use
Postman	Collaborative API development and testing
SoapUI	Testing SOAP and REST APIs
Assertible	Continuous API testing and monitoring
Dredd	HTTP API testing in CI/CD

Your testing strategy should aim for maximal API coverage while minimizing maintenance burden and flaky tests. Prioritize testing critical and complex API flows. Use techniques like data-driven testing to cover more scenarios with fewer tests.

Integrate your API tests into your CI/CD pipeline so they run automatically with every build and deploy. Tests should be reliable, independent, and fast so you can constantly check API health and catch bugs early.

Crucially, don‘t forget to test for the unexpected! Check how your API behaves with missing parameters, invalid data types, huge payloads, and so on. Chaos engineering tools like Gremlin can help stress test your APIs.

With comprehensive automated testing and monitoring in place, you can deploy API changes with more confidence and velocity.

5. Leverage an API Gateway for Consistency and Control

As your API program grows, you‘ll likely end up with a number of different APIs, potentially based on different technologies and owned by various teams. This can lead to inconsistency, duplication, and management headaches.

An API gateway acts as a central entry point that routes requests to the appropriate backend services. It provides a unified facade for your APIs, allowing you to centrally handle cross-cutting concerns like:

• Authentication and authorization
• SSL termination and security policies
• Monitoring and analytics
• Response caching and compression
• Request and response transformations
• Protocol translations (e.g. REST to gRPC)

Netflix relies heavily on API gateways:

"At Netflix, API gateways form the nucleus of our API platform…Gateways provide a single entry point for API requests, allowing us to implement cross-cutting features such as authentication, traffic control, logging, and monitoring across our entire API ecosystem."

Benefits of using an API gateway:

• Consistent API management across diverse backend services
• Central control and visibility over API traffic
• Faster API development by offloading common functionality
• Improved API security via auth, rate limiting, and threat protection
• Decoupled clients and servers for independent evolution
• Support gradual migration between API versions

Popular API gateway solutions include:

Tool	Use
Kong	Open-source API gateway built on NGINX
Amazon API Gateway	Fully managed API gateway service
Apigee	Full lifecycle API management platform
Tyk	Open source API gateway for multi-cloud

When evaluating API gateways, look for features like high performance, extensibility, analytics, and strong community support. For example, Kong‘s plugin architecture allows customizing the gateway with Lua scripting.

Also consider how the gateway fits into your overall API platform strategy. Will you deploy it yourself or use a managed service? How will you configure and provision new gateway instances?

While an API gateway adds some architectural complexity, it‘s an essential tool for managing APIs at scale. It acts as a central clearinghouse for your API ecosystem, giving you visibility and control.

Embrace API Best Practices for Long-Term Success

We‘ve covered five core practices that are essential for building world-class APIs:

1. Design API-first with specs like OpenAPI
2. Secure APIs with defense-in-depth
3. Prioritize developer experience with great docs
4. Test continuously with automation
5. Manage APIs at scale with an API gateway

These practices work together to help you design consistent, secure, reliable APIs that are easy to use and built to evolve. They reflect hard-learned lessons from API pioneers like Stripe, Twilio, and Netflix.

However, adopting API best practices is not a one-time exercise. It requires an ongoing commitment and a culture of excellence. You need to invest in tooling, automation, and training to make these practices a core part of how you design and ship APIs.

But the effort is well worth it. As Twilio CEO Jeff Lawson puts it:

"APIs are the building blocks of modern software. They‘re how developers leverage the work of others to build faster and scale farther. We‘re investing in a future where APIs continue to be at the forefront of innovation."

By embracing API best practices, you‘re not just building better software – you‘re building a better future for your users, developers, and business. You‘re creating APIs that will stand the test of time and help you compete in the API economy.

So don‘t wait to level up your API game. Start small by adopting one practice at a time. Learn from the API community and contribute back your own lessons. Embrace continuous improvement as you hone your API craft.

Together, we can build a world of APIs that are more consistent, interoperable, and empowering for everyone. Let‘s build APIs that last!