API Mocking: The Complete Guide

Have you ever gone on a long hike only to realize that you‘ve been going in circles? That’s what it feels like developing an application without fully understanding how APIs work — cumbersome and aimless.

By coding against flawed mock data, developers get limited feedback and are unable to find problems or identify areas for improvement. Like a true navigator ensuring accuracy from point A to B, mocking is essential for testing your journey through development.

In this blog post, we'll discuss why API mocking is important for quick, quality feedback when building applications — helping put those navigation worries behind you.

Table of Contents

• What is API mocking?
• The Benefits of API Mocking
• API Mocking Examples
• Top Tools for API Mocking

In a nutshell, API mocking is a way of creating realistic examples to simulate the expected response of an API. This involves creating “mock” versions of the various components that make up an API, such as data models and endpoints. You can then interact with them as if they were real APIs.

The Benefits of API Mocking

API mocking can lead to improved quality of software development in a number of ways. Here are some key benefits.

Faster Feedback

Let’s say you’re building an API with data that has yet to be created. Without mocking, you would need to wait until the real data has been required. This slows down the development of your application.

By providing developers with a realistic environment to test their code and test data, API mocking ensures that feedback is more accurate. You can more quickly find bugs, fix them, and optimize your systems. You’ll find yourself with more time instead of butting up against a deadline.

Cost Savings

API mocking can save money in more than one way. The process allows developers to continue working on the project even if the actual API is not yet available or stable. This eliminates the need to wait for the API's availability or pay for third-party services during development.

API mocking also simulates a high load on the system without actually making requests to the real API. This eliminates the need for expensive load testing environments and resources, saving money on infrastructure costs.

Plus, mocking enables faster, parallel development and testing. Developers can work independently without waiting for the actual API to be ready, resulting in significant time and cost savings.

Increased Security

Many teams work with sensitive data. Using real information before an API or app is fully ready leads to security risks. With API mocking, developers are working with fake data, reducing the risk of accessing sensitive information or leaking private data.

Further, mocking APIs allows developers to simulate various scenarios, including negative or malicious inputs, to identify potential vulnerabilities. By doing so, they can proactively fix security flaws or vulnerabilities before they become exploitable in the real system.

Improved Reliability

API mocking allows developers to create specific testing scenarios to simulate different conditions. This includes edge cases, errors, and different input data. By having control over these scenarios, developers can validate the application's behavior and handle these situations in a reliable way.

Additionally, API mocking enables developers to accurately replicate the behavior of the real API. This helps identify potential performance bottlenecks, error handling issues, or compatibility problems and ensures that the application performs reliably under different conditions.

Cross-Platform Compatibility

API mocking allows developers to simulate responses from different platforms or systems. This allows them to test the compatibility of their application with various APIs. This ensures that their app can handle the responses appropriately across multiple platforms.

API Mocking Examples

API mocking is a powerful tool that can provide huge benefits to teams who are developing applications. Here are some of the most common examples of when a team might use mock APIs.

Prototyping

API mocking can be used to quickly build and test a prototype of an application without having to rely on real APIs. This is especially useful for early-stage startups who need to develop quick prototypes in order to get funding or attract business partners.

Automated Testing

Mocking allows developers to run tests on their code and get accurate feedback. You can then build an end product with fewer bugs and increased functionality.

API mocking can be used in automated testing to ensure that an application's performance is not affected by changes in the external APIs it relies on. This is especially beneficial for companies that have frequent updates to their products.

Debugging

Using API mocking, developers can capture and replay specific API responses, allowing them to reproduce issues and debug them in a controlled environment. This makes it easier to analyze and identify the root causes of bugs, as they can repeatedly trigger the problematic scenario.

API mocks can also be used to quickly identify errors in an application without having to access real data.

Integrating a Third-Party API

If you’re going to integrate a third-party API into your application, API mocking can help you at every step.

API mocking enables developers to start working on the integration even before the actual third-party API is available. By mocking the API endpoints and responses, developers can begin testing the integration logic without the finished third-party API.

With API mocking, developers can also decouple their application from the actual third-party API during testing. This eliminates the need to rely on the stability or rate limits of the external API. Development progress won’t be hindered by external factors.

Finally, API mocking provides a controlled environment where developers can verify that their application correctly interacts with the third-party API. Developers can simulate various responses without making actual requests to the live API, making it easier to isolate issues.

Launching New Features

By creating mock versions of APIs, teams can ensure their code is functioning properly before pushing any changes live. Developers can identify and address potential issues in new features early. By simulating different scenarios, developers can quickly uncover and debug issues before the feature is released to users.

Running Performance Tests

By running tests against virtual APIs, teams can identify performance issues and tweak their code in order to optimize the application. API mocking ensures that the responses are consistent, allowing you to replicate the same test scenarios repeatedly. This helps in comparing and analyzing test results more effectively.

Top Tools for API Mocking

API mocking is an invaluable tool in the software development process. Here are some of the top tools for API mocking.

1. Mockoon

Mockoon is an open-source tool that makes it easy to create, configure and deploy mock APIs. It has a simple UI that allows users to quickly build their own mocks using predefined templates. You can run your mock application in a serverless, headless, or automated environment.

Mockoon also allows you to serve your mock API over TLS with a custom certificate.

What we like: You don’t even need an account to start testing your application with Mocky. Their platform makes getting started a frictionless experience.

Price: Free.

2. Stoplight

Stoplight provides an intuitive platform for creating and managing mock APIs with automated testing and debugging capabilities.

Stoplight offers a rich ecosystem of integrations, including popular development tools, version control systems, and Continuous Integration/Continuous Deployment (CI/CD) pipelines. This allows you to incorporate Stoplight's API mocking capabilities into your existing development processes with ease.

What we like: With Stoplight, you have the ability to reuse models and components, allowing you to effortlessly create high-quality APIs every time.

Price: Plans start at $39 per month.

3. Postman

Postman allows users to create and manage mock APIs with ease, and it has a wide range of features for customizing mocks and testing code.

Postman offers flexibility in defining and customizing mock server responses. You can specify response headers, delay times, status codes, and content, including JSON, XML, and other data formats. This allows you to simulate different API behaviors and test error handling.

What we like: Postman facilitates team collaboration through its cloud-based platform. You can share mock servers with team members, collaborate on the APIs, and gather feedback directly within the tool.

Price: Plans start at $12 per month.

4. Mountebank

Mountebank is an open-source tool that makes it easy to create mock APIs. The platform offers a variety of features for customizing responses and testing code. Mountebank supports multiple protocols, including HTTP, HTTPS, TCP, and SMTP. This flexibility allows you to mock APIs and services across different protocols, making it suitable for a wide range of use cases.

What we like: Mountebank provides a record and replay feature that allows you to capture and store real API interactions as a mock. This is especially useful when you need to quickly create a mock based on real-world requests.

Price: Free

5. Apiary

Apiary is a cloud-based platform for creating, managing, and deploying mock APIs. Apiary uses the Blueprint language, a Markdown-like syntax, to define API design and documentation. This makes it easy to create human-readable API descriptions that can be used for mocking and documentation purposes.

What we like: Apiary promotes a “design-first” approach to API development, where the API design is defined and documented before the implementation. This ensures a well-structured and well-documented API from the beginning.

Price: Free plans are available.

6. MockServer

MockServer is an open-source tool that makes it easy to create and manage mock APIs. MockServer offers extensive request-matching capabilities, allowing you to define complex match criteria based on HTTP methods and query parameters. This enables you to precisely match and respond to different types of requests.

What we like: MockServer can act as a proxy server, allowing you to record real-world API interactions and create mocks based on observed patterns.

Price: Free.

7. Hoverfly

Hoverfly is an open-source tool with automated response validation capabilities. Hoverfly acts as a transparent HTTP proxy, intercepting API requests and responses without requiring any client-side code changes. This makes it easy to integrate Hoverfly into existing applications and testing setups without modifying your application's code.

What we like: Hoverfly enables you to simulate different network conditions like latency, bandwidth limitations, or packet loss to emulate real-world network environments.

Price: Free.

8. WireMock

WireMock is an open-source tool that makes it easy to customize responses and test code.

WireMock operates as an HTTP server, allowing you to define and configure mock endpoints using simple JSON/XML configurations or through a Fluent Java API. It supports both request matching and response generation, making it easy to create detailed mock APIs.

What we like: WireMock provides a record and playback feature that allows you to capture real API interactions and automatically generate corresponding mock endpoints.

Price: Free.

9. Prism

Prism is an open-source tool that makes it easy to create, configure and deploy mock APIs with automated testing capabilities.

Prism can be seamlessly integrated into your existing development workflow. It provides a simple CLI interface and can be used as a standalone server or embedded into your application as a library.

What we like: Prism uses a configuration file (usually in YAML or JSON format) to define the mock server behavior. This approach decouples the API mocking logic from the actual code. You can then make changes and updates without touching the codebase.

Price: Free.

10. Mocky

Mocky is a cloud-based platform for creating and managing mock APIs with automated testing capabilities. Mocky allows for instant API mocking by just providing the URL, HTTP method, and response body directly in the web interface. There is no need for any setup or waiting time.

What we like: Mocky is free to use. There are no ads, hidden subscriptions, or service limits. Plus, your mocks will be available forever if you call it at least once time per year.

Price: Free.

Getting Started with API Mocking

API mocking is a valuable tool in the software development process. It can save time, money, and effort when building applications.

There are many tools available for creating and managing mocks, each with its own features and capabilities. By choosing the right tool for your project, you can ensure that your API mocking process is as efficient and effective as possible.