Toolpaper

Send multipart form-data with cURL in C#

Paste a curl command that sends multipart form-data and get idiomatic C# code. We pick the right serialization for HttpClient and set the correct Content-Type.

Quick answer

To convert a cURL command to C#, paste it into the Toolpaper workbench below. It parses the command in your browser and emits idiomatic C# code — headers, query string, request body, authentication (Bearer, Basic, API key), and cookies are all wired up automatically. No data is uploaded; conversion is fully client-side.

Prefer a different target? See the full cURL to C# reference, or jump to the same guide in JavaScript, Node.js, or Python.

InputcURL command
MethodPOST·Headers0·Body—·Form2 fields· Chars 100
Output.NET · HttpClient(.NET)
using System;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;

class Program {
  static async Task Main() {
    using var handler = new HttpClientHandler { AllowAutoRedirect = false };
    using var client = new HttpClient(handler);
    using var request = new HttpRequestMessage(new HttpMethod("POST"), "https://api.example.com/upload");
    var content = new MultipartFormDataContent();
    var _fs_file = System.IO.File.OpenRead("/path/to/photo.png");
    var _fc_file = new StreamContent(_fs_file);
    _fc_file.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
    content.Add(_fc_file, "file", "/path/to/photo.png");
    content.Add(new StringContent("Hello"), "caption");
    request.Content = content;
    using var response = await client.SendAsync(request);
    var text = await response.Content.ReadAsStringAsync();
    Console.WriteLine(text);
  }
}
Inspect

Example

A representative curl command for this scenario. Paste your own above to convert an exact match.

curl input
curl -X POST https://api.example.com/upload \
  -F "file=@/path/to/photo.png" \
  -F "caption=Hello"

Implementation notes

  • Content-Type is detected from -H headers first, then inferred from the body shape when the header is missing.
  • Each -F flag becomes a distinct part; file@ paths are surfaced as HttpClient file handles so the multipart boundary stays valid.
  • Charset directives on Content-Type (e.g. application/json; charset=utf-8) survive the round trip.

Common mistakes

  • Setting Content-Type manually and then also using HttpClient's helper — you end up with duplicate headers or the wrong one wins.
  • Forgetting @ in -F "file=@upload.png" — without it curl sends the literal string, not the file. The generator flags this.
  • Trusting the browser DevTools "Copy as cURL" to preserve charset — it often drops it. Clean panel restores common defaults.

Common questions

How is multipart form-data encoded in the generated C#?
-F flags translate to multipart form-data with proper boundary handling — files={...} in Python, MultipartFormDataContent in C#, MultipartBody.Part in Java/Kotlin.
Does it preserve Content-Type?
Yes. The Content-Type header is honored and matched against the body so serialization stays consistent.
Is anything uploaded?
No. Parsing and generation happen entirely in your browser.

More payload types in C#

C# hub →

JSON in C#

/how-to/send-json-with-curl-in-csharp

form-urlencoded in C#

/how-to/send-form-with-curl-in-csharp

XML in C#

/how-to/send-xml-with-curl-in-csharp

GraphQL in C#

/how-to/send-graphql-with-curl-in-csharp

The same guide in other languages

All guides →

In JavaScript

/how-to/send-multipart-with-curl-in-javascript

In Node.js

/how-to/send-multipart-with-curl-in-node

In Python

/how-to/send-multipart-with-curl-in-python

In Go

/how-to/send-multipart-with-curl-in-go

In PHP

/how-to/send-multipart-with-curl-in-php

In Ruby

/how-to/send-multipart-with-curl-in-ruby

In Rust

/how-to/send-multipart-with-curl-in-rust

In Java

/how-to/send-multipart-with-curl-in-java

Full C# reference on the cURL to C# hub, or open the main converter for all 18 targets.