API Mocking: 9 Tools Compared

When developing a frontend or a certain service, parts of the software often require either a backend or certain APIs (be it external or internal). However, the other side is not quite ready yet or is too costly to be used in the development process. This is where API mocking and service virtualization (on a broader scale) become invaluable.

An API mocking tool allows the creation of realistic stand-ins, or mocks, for APIs that might be slow, unreliable, or not yet built. By simulating the expected responses and behaviors of these APIs, one can isolate and thoroughly test the application's logic, front-end, and integrations without any external dependencies. A discussion on some of the popular API mocking tools is provided below.

These tools offer a unique set of features, from quick, friction-less setup to advanced state management, to aid speeding up the development process. The primary focus of the article will be on ease of use and feature richness.

Here is a table depicting the feature matrix of all the products:

Feature/Characteristic	Beeceptor	Apidog	WireMock Cloud	ReadyAPI	MockServer	Mountebank	Mockoon	Requestly	Zuplo
Connectivity	Cloud / On-premise	Cloud / On-premise	Cloud / On-premise, Self-hosted (OSS)	Cloud / Desktop App	Self-hosted	Self-hosted	Self-hosted	Cloud / On-premise	Cloud / On-premise
Tools provided	CLI, Online	Desktop, Online	Online	Desktop	CLI, Java API, Docker, etc.	CLI	Online, Desktop	Online, Desktop	Online
Licensing	Freemium	Freemium	Free (OSS), Paid (Cloud)	Hidden	Free & Open Source	Free & Open Source	Free (OSS), Paid (Cloud)	Freemium	Freemium
Billing	Per usage	Per seat	Per seat	Per seat	-	-	Per seat	Per seat	Per seat / usage
Data generation	✅	✅	✅	✅	✅	✅	✅	✅	✅
Templating	✅	✅	✅	❌	✅	✅	✅	✅	✅
Stateful Mocking	✅	✅	✅	✅	✅	✅	✅	✅	✅
Adv. State Management	✅	❌	❌	❌	✅	❌	❌	❌	✅
CRUD routes	✅	✅	✅	✅	✅	✅	✅	✅	✅
Callouts	✅	✅	✅	✅	✅	✅	✅	❌	✅
Proxying	✅	✅	✅	✅	✅	✅	✅	❌	✅
Request Matching	✅	✅	✅	✅	✅	✅	✅	❌	✅
API Technologies	HTTP/HTTPS, SOAP, gRPC, GraphQL	HTTP/HTTPS, SOAP	HTTP/HTTPS, SOAP, gRPC, GraphQL	HTTP/HTTPS, SOAP, GraphQL	HTTP/HTTPS, SOAP, GraphQL	HTTP/HTTPS, SOAP, TCP, SMTP	HTTP/HTTPS	HTTP/HTTPS, SOAP, GraphQL	HTTP/HTTPS, SOAP
Enterprise support	✅	✅	✅	✅	❌	❌	✅	✅	✅

Beeceptor

Beeceptor's initial setup is very quick and fantastic. One can create mock endpoints and jump straight into debugging with minimal friction. It proves super handy for quick API mocking and enabling thorough testing across different scenarios, making it excellent for efficient webhook testing and rapid mock API creation.

What truly sets Beeceptor apart are its advanced features, particularly in the paid tiers. Its advanced stateful mocking is arguably the most feature-rich compared to all its competitors; there is a dedicated state management menu and CRUD routing rules to mimic CRUD operations, which is a huge time-saver for building complex simulations. Plus, the platform is capable of target proxying, letting traffic be intercepted on an existing API and selectively mocking certain routes. There's also a role-based sharing feature which enables collaboration.

The main issue is that Beeceptor, by default, is a cloud-native solution (although, an on-premise option also exists). Also, while the free plan is sufficient for small projects, using it for enterprise testing may feel limited. That being said, the paid plans are also the cheapest compared to all its competitors, and the support team is outstanding; a few minor bugs were found and some gaps in documentation, but the staff were genuinely helpful and responded quickly.

Apidog

Apidog is a comprehensive API lifecycle manager that offers a lot of functionality as an API tool. It features a sleek, modern, and clean user interface in its web application. With support for seamless integrations and robust documentation, the platform is designed to facilitate collaborative and efficient API management for both SMEs and enterprises, aiding in real-time decision-making.

However, the extensive feature set can result in a steep learning curve, potentially complicating the initial setup process. Less experienced developers may find it challenging to fully navigate the UI and utilize all of the tool's capabilities. Furthermore, some users have reported limitations concerning its scheduling features and the lack of granularity on failure notifications.

WireMock Cloud

WireMock is yet another really impressive API mocking tool with its power for complex scenarios. Its service mocking capability is invaluable, allowing response simulations without reliance on live environments. The plain, simple and modern GUI simplified creating and managing mocks, even for intricate setups. Data source management was yet another handy tool that allowed dealing with external test data sources.

Now to drawbacks, the first issue was that setup required too much configuration boilerplate, making stub maintenance time-consuming for large APIs. Debugging felt tricky, with a lot of steps. The admin APIs felt difficult to work with, and its state management options were hidden in individual stubs instead of being a dedicated dashboard menu.

Finally, the pricing. Though the 30-day enterprise trial was fair, the basic free plan felt so limited. The undisclosed enterprise fee suggests a flexible but potentially high cost model, complicating budgeting. Wiremock, however offers a generous knowledge base; a series of informative videos on YouTube and a dedicated page to train new users.

ReadyAPI

ReadyAPI must have been built for enterprise testing in mind. The UI’s organized structure made API arrangement easy, and test case automation was straightforward. The in-built features, like assertions, data sink, and data source were found to be very useful.

Also, integration with CI/CD tools like Git, Jenkins, and Docker, plus excellent reporting, felt like a neat solution for developer pipeline needs. Securely sharing API sets across the team also felt like a bonus.

The drawbacks, however, felt significant too. The undisclosed pricing created a barrier. Performance often suffered, feeling a bit slow, and the application's stability felt shaky at times. The UI often felt dated and restrictive (just like SOAPUI), limiting workflow.

MockServer

MockServer is an open-source tool for API mocking. Its configuration and wide deployment options (Docker, Java, Node.js) made it pretty versatile. Its advanced matching for complex JSON bodies is a very useful asset for precise testing scenarios. Its support for multiple protocols, including WebSockets, was also a huge benefit for integration work, and since the tool was open source, it felt like a major win for implementing robust, enterprise-grade mocking. This is also a great option for people who want to work with sensitive data in their APIs.

However, using MockServer demanded significant time and effort. Also, the overall implementation often felt complex, and getting advanced features running required deep configuration: the documentation gaps and limited examples for complex use cases were a major pain point. What was also noticed was the absence of built-in recording/replaying and native OpenAPI integration.

Mountebank

Mountebank is a free and open-source tool, offering service virtualization without any licensing costs. This means that Mountebank can be run virtually anywhere, giving developers absolute control and a zero-dependency setup for rapid, isolated testing.

The multi-protocol support, i.e., native handling of HTTP, HTTPS, TCP, and SMTP, made it versatile for various enterprise integration points. What was impressive was its ease of use CLI workflow, even while providing features like complex JSON-based stubs, dynamic response generation, and advanced matching rules. Its command-line and REST API for automation enable dynamic working, which is essential for continuous integration pipelines and sophisticated, stateful testing scenarios.

However, the lack of native WebSockets support felt like an immediate downside. Also, Mountebank has no graphical user interface. So, managing a large number of mocks without a visual interface meant heavy reliance on configuration files, making it harder for non-developers to manage. Furthermore, it lacked request validation or schema enforcement, putting the burden on the user to implement separate checks to ensure the API contracts remained accurate at scale.

Mockoon

Mockoon is a free and open-source tool, meaning one could just download it and get started with mocking without needing to create an account, which makes deployment straightforward, although a paid cloud plan is also offered. The user interface is clean, so getting the first mock API up and running was a breeze. For teams starting out or needing a quick, no-fuss solution, this accessibility is a huge win.

The features for deeper testing were definitely present. CRUD routes can be leveraged using data buckets to build a mock REST API that could actually store and update data. This lets more complex scenarios be tested, which is critical for realistic front-end development. However, there was a serious limitation with advanced stateful mocking features, which made it feel very limited.

While the feature set is robust, the documentation for user-experience could be better. There are not enough examples, and one often has to dig around a bit to figure out how to use some of the options. If a fully-featured, community-driven tool is sought, and a little experimentation is acceptable, Mockoon offers a lot of power without any financial barrier. A paid cloud version is also offered.

Requestly

Requestly, by BrowserStack, while also available as a desktop app, is primarily a cloud-based tool. It comes as a Chrome extension, as well as a web app. The setup process was simple, except the account confirmation mail which took a lot of time. Only the cloud tool served its purpose, since mocking was only possible on its cloud option which required an account, which again, took a lot of time to create.

Also, the learning curve for setting up felt very complex, and even pretty time-consuming. For advanced mocking, the limitations stood out. There is no advanced stateful mocking, and there was no way to set up CRUD routes. The one drawback that stood out the most was the fact that an account was needed to actually be able to use the tool, and the whole process was quite slow. And the pricing felt too steep!

Zuplo

For Zuplo, the initial learning curve felt very difficult. This platform doesn't feel like a no-code/ low-code solution, and while not impossible to learn, all of this feels too time-consuming for an API mocking platform. Getting past the learning to benefit from its features felt like a major hurdle. That aside, it has a host of handy features not seen in other mock tools, and it also is capable of both advanced stateful mocking and CRUD routing.

Once past the steep learning cliff, the platform can be productive. However, just to reiterate, the time and energy spent on just learning the platform may outweigh the benefits, especially if a new user is involved. This is a platform that strongly aligns with experienced devs who want all the flexibility they get with writing code. The good part about Zuplo is that their free plan is very generous.

Conclusion

API Mocking tools are crucial because they significantly significantly reduce development time. Among the many tools discussed, following tools stand out: Beeceptor, Mockoon, WireMockCloud, Apidog and Zuplo.

However, considering ease of use and feature richness, Beeceptor stands out from the rest. Its no-code platform not only makes it easy for beginners, but its powerful handlebars template enabled features (like state management, faker and other miscellaneous helper statements), and rule based features (like response weights, callouts, proxy, CRUD routes, request matching), flexible pricing and even an option to set up on-premise makes this the most preferred tool for API mocking.