Asp net core ajax requests gives 400 bad request but postman works


ASP.NET is a popular programming language used for building web applications. One issue that developers face is when ASP.NET Core AJAX requests give a 400 Bad Request error, while the same request works fine in . In this article, we will explore the possible causes of this issue and provide with examples.

Possible Causes

There can be several reasons why ASP.NET Core AJAX requests give a 400 Bad Request error while Postman works fine. Let's discuss some of the common causes:

1. Invalid Request Data

One possible cause is that the AJAX request is sending invalid data to the server. This can happen if the request payload is not properly formatted or if the required parameters are missing. To troubleshoot this issue, you can check the request payload and ensure that it the format.

    url: '/api/example',
    method: 'POST',
    data: JSON.stringify({ name: 'John', age: 25 }),
    contentType: 'application/json',
    success: function(response) {
    error: function(xhr, status, error) {

2. CORS (Cross- Resource Sharing) Issue

Another possible cause is a CORS issue. CORS is a security mechanism that restricts AJAX requests to only be made to the same origin (domain, protocol, and port) as the web application. If the server does not cross-origin requests, it can result in a 400 Bad Request error. To solve this issue, you need to configure the server to allow cross-origin requests.

// Startup.cs

public void ConfigureServices(IServiceCollection services)
    services.AddCors(options =>
            builder =>

    // Other configurations...

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)

    // Other configurations...

3. Server-side

It is also possible that the server-side validation is rejecting the AJAX request due to some validation rules. In this case, the server may be expecting certain data or parameters that are not being sent correctly. You can check the server-side code and ensure that the request is being processed correctly.

// Controller.cs

public IActionResult Example([FromBody] ExampleModel )
    if (!ModelState.IsValid)
        return BadRequest(ModelState);

    // Process the request...

    return Ok();


When ASP.NET Core AJAX requests give a 400 Bad Request error while Postman works fine, it can be due to various reasons such as invalid request data, CORS issues, or server-side validation. By troubleshooting these possible causes and the appropriate solutions, you can resolve this issue and ensure that your ASP.NET Core AJAX requests work correctly.

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