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Using HttpClient to POST JsonObject from a Web API


I’m trying to use HttpClient from Web API to POST a JsonObject. I’m not sure how to proceed and can’t seem to locate anything in the way of sample code.

Here’s what I’ve come up with thus far:

var myObject = (dynamic)new JsonObject();
myObject.Data = "some data";
myObject.Data2 = "some more data";

HttpClient httpClient = new HttpClient("myurl");
httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

HttpResponseMessage response = httpClient.Post("", ???);

I believe I need to cast my JsonObject as a StreamContent, but I’m having trouble doing so.

Asked by Mark

Solution #1

It would be: with the new version of HttpClient and without the WebApi package:

var content = new StringContent(jsonObject.ToString(), Encoding.UTF8, "application/json");
var result = client.PostAsync(url, content).Result;

Alternatively, if you want it to be asynchronous:

var result = await client.PostAsync(url, content);

Answered by pomber

Solution #2

The simplest method is to use a StringContent with your JSON object’s JSON representation.

    new StringContent(

Answered by carlosfigueira

Solution #3

You might alternatively use the HttpClientExtensions.PostAsJsonAsync method, depending on your.NET version.

Answered by user3285954

Solution #4

If using Newtonsoft.Json:

using Newtonsoft.Json;
using System.Net.Http;
using System.Text;

public static class Extensions
    public static StringContent AsJson(this object o)
        => new StringContent(JsonConvert.SerializeObject(o), Encoding.UTF8, "application/json");


var httpClient = new HttpClient();
var url = "";
var data = new { identifier = "username", password = "password" };
var result = await httpClient.PostAsync(url, data.AsJson())

Answered by Matthew Steven Monkan

Solution #5

I don’t have enough reputation to remark on pomber’s answer, so I’m going to post another one. I kept getting a “400 Bad Request” answer from an API I was POSTing my JSON request to using pomber’s method (Visual Studio 2017, .NET 4.6.2). The issue was eventually identified down to an improper “Content-Type” header provided by StringContent() (see


To appropriately set the header on the request, use pomber’s answer with an extra line:

var content = new StringContent(jsonObject.ToString(), Encoding.UTF8, "application/json");
content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
var result = client.PostAsync(url, content).Result;

Answered by anthls

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