How do you set the Content-Type header for an HttpClient request? – Dev

The best answers to the question “How do you set the Content-Type header for an HttpClient request?” in the category Dev.


I’m trying to set the Content-Type header of an HttpClient object as required by an API I am calling.

I tried setting the Content-Type like below:

using (var httpClient = new HttpClient())
    httpClient.BaseAddress = new Uri("");
    httpClient.DefaultRequestHeaders.Add("Accept", "application/json");
    httpClient.DefaultRequestHeaders.Add("Content-Type", "application/json");
    // ...

It allows me to add the Accept header but when I try to add Content-Type it throws the following exception:

Misused header name. Make sure request headers are used with
HttpRequestMessage, response headers with HttpResponseMessage, and
content headers with HttpContent objects.

How can I set the Content-Type header in a HttpClient request?


For those who didn’t see Johns comment to carlos solution …

req.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");


The content type is a header of the content, not of the request, which is why this is failing. AddWithoutValidation as suggested by Robert Levy may work, but you can also set the content type when creating the request content itself (note that the code snippet adds application/json in two places-for Accept and Content-Type headers):

HttpClient client = new HttpClient();
client.BaseAddress = new Uri("");
      .Add(new MediaTypeWithQualityHeaderValue("application/json"));//ACCEPT header

HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, "relativeAddress");
request.Content = new StringContent("{\"name\":\"John Doe\",\"age\":33}",
                                    "application/json");//CONTENT-TYPE header

      .ContinueWith(responseTask =>
          Console.WriteLine("Response: {0}", responseTask.Result);


try to use TryAddWithoutValidation

  var client = new HttpClient();
  client.DefaultRequestHeaders.TryAddWithoutValidation("Content-Type", "application/json; charset=utf-8");


If you don’t mind a small library dependency, Flurl.Http [disclosure: I’m the author] makes this uber-simple. Its PostJsonAsync method takes care of both serializing the content and setting the content-type header, and ReceiveJson deserializes the response. If the accept header is required you’ll need to set that yourself, but Flurl provides a pretty clean way to do that too:

using Flurl.Http;

var result = await ""
    .WithHeader("Accept", "application/json")
    .PostJsonAsync(new { ... })

Flurl uses HttpClient and Json.NET under the hood, and it’s a PCL so it’ll work on a variety of platforms.

PM> Install-Package Flurl.Http