Lecture 13: Troubleshooting a REST API in Visual Studio with Postman

REST API Development: Build, Test, Troubleshoot

During REST API development, errors and unexpected behaviors are common. Troubleshooting is an essential skill that allows developers to identify issues quickly and ensure the API works correctly.

Two of the most powerful tools for debugging and testing REST APIs are Visual Studio and Postman. Together, they allow developers to run the API locally, inspect code execution, and test endpoints with real HTTP requests.

Running the API in Visual Studio

Visual Studio allows developers to run and debug REST APIs directly from the development environment. When the API is started, it typically runs on a local server.

Example local API address:

This address can then be used to test endpoints through tools like Postman.

Using Breakpoints for Debugging

One of the most useful debugging techniques in Visual Studio is using breakpoints.

• A breakpoint pauses code execution
• Allows inspection of variables
• Helps identify where errors occur

For example, placing a breakpoint inside a controller method allows developers to see the exact values received from a request.

Testing the API with Postman

Postman is a popular tool used to send HTTP requests to APIs. It allows developers to test endpoints without needing a frontend application.

Example request tested in Postman:

After sending the request, Postman displays the server response, including the returned JSON data and HTTP status code.

Common Issues When Testing APIs

When testing a REST API, developers may encounter several common issues:

• Incorrect endpoint URLs
• Missing route configuration
• Database connection errors
• Incorrect HTTP methods
• Serialization or JSON formatting issues

Identifying these problems early helps maintain a stable API.

Checking HTTP Status Codes

Postman also displays HTTP status codes returned by the server, which help diagnose problems.

• 200 OK – Request successful
• 400 Bad Request – Invalid request data
• 404 Not Found – Endpoint not found
• 500 Internal Server Error – Server-side issue

These codes provide valuable clues when troubleshooting API problems.

Best Practices for Troubleshooting

• Test endpoints individually
• Use breakpoints to inspect execution flow
• Check HTTP status codes carefully
• Verify JSON responses
• Log errors when possible

Following these practices makes debugging faster and more efficient.

Next Steps

After mastering troubleshooting techniques, developers can confidently test and refine their REST APIs, ensuring that endpoints behave correctly before integrating them with frontend applications or external services.