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Home / Tutorials / API Mocking: Concept, Free Tool & Real-world Examples

API Mocking: Concept, Free Tool & Real-world Examples

API mocking is crucial in modern software development, enhancing efficiency and speed. By simulating APIs, developers and testers can work with predefined responses, reducing dependencies on real APIs and enabling parallel development.

APIs (Application Programming Interfaces) have become the backbone of modern software development, enabling applications to communicate with each other seamlessly. As the demand for faster and more efficient development cycles grows, developers are increasingly turning to API mocking to streamline the process. This blog explores the concept of API mocking, its benefits, free tool, best practices and real-world examples.

What is APl Mocking?

API mocking involves creating a simulated version of an API that mimics the behavior of a real API. This simulated API can provide predefined responses to various requests, allowing developers and testers to work with the API even when the actual implementation is not available or incomplete. By using mock APIs, teams can accelerate development cycles, enhance testing processes, and improve productivity.

Apidog is a leading free tool for API mocking, offering smart mocking rules, customizable data, and endpoint-specific configurations to simulate realistic API behaviors effectively.

What is the Difference between Mock API and Real API?

Developers and testers often work with two primary types of APIs: Mock APIs and Real APIs. Understanding the differences between these two is crucial for efficient development and testing.

Mock API

Definition: A Mock API is a simulated version of a real API. It mimics the behavior and responses of a real API but does not perform any actual data processing or operations. Mock APIs are used primarily for testing and development purposes.


  1. Predefined Responses: Mock APIs return predefined responses based on the request parameters. These responses are usually set up during the creation of the mock API.
  2. No Backend Processing: Since Mock APIs are simulations, they do not connect to a database or perform any backend processing. The responses are static and based on predefined rules.
  3. Used for Testing and Development: Mock APIs are used when the real API is not available, incomplete, or unstable. They enable developers to continue their work without dependency on the actual API.
  4. Controlled Environment: Mock APIs provide a controlled environment for testing various scenarios, including edge cases and error conditions, which might be difficult to reproduce with a real API.
  5. Faster Development Cycles: By using mock APIs, front-end and back-end developers can work in parallel, speeding up the development process. It also allows for early testing and validation of the API contract.

Real API

Definition: A Real API is the actual implementation of an API that performs operations, processes data, and interacts with other systems or databases. It provides real-time, dynamic responses based on the logic and data defined in the backend.


  1. Dynamic Responses: Real APIs provide dynamic responses based on the actual processing of requests. These responses can vary depending on the current state of the data and the logic implemented in the API.
  2. Backend Processing: Real APIs connect to databases, services, and other systems to process requests and generate responses. This includes performing CRUD (Create, Read, Update, Delete) operations, running business logic, and integrating with other APIs.
  3. Used in Production: Real APIs are used in live environments where actual data processing is required. They are critical components of deployed applications, handling real user requests and providing necessary functionality.
  4. Real-World Conditions: Real APIs operate in real-world conditions, dealing with actual data, load, and network conditions. This makes them suitable for performance testing, load testing, and end-to-end testing.
  5. Security and Compliance: Since real APIs interact with actual data, they need to be secured and compliant with relevant regulations and standards. This includes implementing authentication, authorization, and data encryption mechanisms.

Key Differences


  • Mock API: Used for testing and development.
  • Real API: Used in production and live environments.


  • Mock API: Returns static, predefined responses.
  • Real API: Returns dynamic responses based on actual data processing.

Backend Interaction:

  • Mock API: Does not perform any backend operations.
  • Real API: Connects to databases and services to process requests.

Usage Scenarios:

  • Mock API: Ideal for early development stages, parallel development, and testing edge cases.
  • Real API: Suitable for performance testing, end-to-end testing, and production use.


  • Mock API: Provides a controlled environment for testing.
  • Real API: Operates in real-world conditions with actual data and load.

Both Mock APIs and Real APIs play crucial roles in the software development lifecycle. Mock APIs facilitate faster development and thorough testing by simulating the real API’s behavior. On the other hand, Real APIs provide the actual functionality and data processing required for live applications.

Benefits of API Mocking

  1. Parallel Development: Front-end and back-end developers can work simultaneously. Front-end developers can use mock APIs to build and test the user interface while the back-end team develops the actual API​​.
  2. Improved Testing: Testers can simulate different scenarios, including edge cases and error conditions, ensuring thorough testing of the application.
  3. Reduced Dependencies: Development and testing can proceed without waiting for the actual API to be ready or stable, minimizing bottlenecks in the workflow.
  4. Enhanced Collaboration: Clear API specifications and mock implementations foster better communication and understanding among team members.

The Best Free Tool for API Mocking– Apidog

What is Apidog?

Apidog is a comprehensive and free API development platform designed to streamline every phase of the API lifecycle, from design and debugging to testing and mocking. Among its standout features is API mocking, which empowers developers to simulate backend services effortlessly and mock data of different kinds without much need for configurations or coding.

Key Features of Apidog’s API Mocking with Use Case

1. Use built-in smart API mocking rules to fetch realistic response data: Apidog leverages built-in smart mocking rules to automatically generate dummy but reasonable data based on API specifications created at Apidog. Developers can create mock APIs with minimal configuration—simply create an endpoint, define request and response parameters, and click "send" to receive response data and a test report. Apidog intuitively understands and simulates the required data.

Use Case: If a field name contains terms like "image," "time," or "city," Apidog's mocking server generates realistic mock data such as image URLs, timestamps, or city names.

Use Apidog to get API mocking data

2. Customize API mocking rules: While Apidog offers a wide range of common fields ready for use, it also allows you to create customized data rules for API mocking according to your specific business needs.

Use Case: If you need to mock an Order ID that always begins with "DD," and this rule isn't available in Apidog's default options, you can customize your own mocking rule using the built-in visual data rule creator. Navigate to "Settings," find "Mock Setting," and click "+New" in the "Custom Matching" section. Edit the data type and write a regular expression to define the mocking data.

Create customized API mocking rule with Apidog

3. Customize API mocking data at the endpoint level: Apidog allows you to define the response data type at the endpoint level. This is useful for uncommon data specified for a particular endpoint.

Use Case: If your application users have only two roles—reader and creator—you can configure the mocking data to include only these roles by setting them in the advanced settings, where JSON Schema is supported.

Define API mocking data rule for specific endpoint field

4. Define desired API data response types using built-in mocking rules: Apidog fetches mocking data according to your defined fields automatically. You can ensure it fetches the specific type of data you need by setting it up in the "Mock" section for that field.

Use Apidog's built-in mocking rule to define desired API data response type

Use Case: For a field named "name" where you need a company name, select "company.name" from the list of mocking rules to receive a dummy company name in the API response.

5. Set up API conditional response using Advanced Mocking: Apidog's Advanced Mocking enables you to configure conditional responses based on request parameters.

Apidog's advanced mocking feature

Use Case: If users require profiles for creators, the API can respond with the profiles of creators. Set up expectation rules in Apidog’s Advanced Mock feature, then customize the API response data either manually or by using the "Generate Automatically" feature.

6. Use custom scripts to define mocking rules: When predefined settings aren't sufficient for your needs, you can use custom scripts in Advanced Mock to define specific rules.

Use custom script to set up desired API response data

Use case: To ensure API responses only contain valid page numbers, create a custom script to prevent fetching nonsensical data, such as requesting page 4 when there are only 3 total pages.

Check out more information about Advanced Mocking here:

Advanced Mock | Apidog
View details for advanced mock here.

Real-World Examples of API Mocking

1. E-Commerce Development

In an e-commerce project, the front-end team can use mock APIs to simulate product listings, user accounts, and shopping cart functionalities while the back-end team works on the actual API. This enables the front-end team to develop and test the user interface without waiting for the back-end services to be completed.

2. Mobile App Development

Mobile app developers often rely on mock APIs to simulate server responses for various user actions such as login, fetching data, and posting updates. This allows them to test the app’s behavior in different scenarios and ensure that the app handles responses correctly, even when the actual API is not yet available.

3. Continuous Integration/Continuous Deployment (CI/CD)

In CI/CD pipelines, mock APIs are used to run automated tests consistently. Since mock APIs provide predictable responses, they help in verifying the functionality of the application in a controlled environment. This ensures that any issues are identified and resolved early in the development process.

4. Microservices Architecture

In a microservices architecture, different services communicate via APIs. Mock APIs can simulate the behavior of dependent services, allowing developers to test their microservices in isolation. This helps in identifying issues and dependencies without requiring the entire system to be up and running.


API mocking is essential for modern software development, allowing developers to simulate APIs with predefined responses. This practice accelerates development, enhances testing, and reduces dependencies on real APIs, fostering efficient collaboration and faster delivery.

Apidog stands out as an exceptional free tool for API mocking, offering features like smart mocking rules, customizable data rules, and endpoint-specific configurations. These capabilities allow developers to simulate realistic API behaviors, ensuring comprehensive testing and smooth development cycles.

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