使用Visual Studio做性能测试时API报415 Unsupported Media Type错误求助

Hey there, let's work through this 415 error together—this is a super common gotcha when setting up POST requests in Visual Studio's performance testing tools, so I'll walk you through the most likely fixes:

1. Confirm you're sending a valid Content-Type header #

415 errors almost always boil down to the server not recognizing the media type of your request, or the header being missing entirely. Even if you copied headers from Fiddler, Visual Studio's load test settings might be overriding or omitting this critical header. Here's what to do:

• Open your request configuration in Visual Studio and navigate to the Headers section.
• Explicitly add the header that matches your request body format:
  • For JSON payloads: Content-Type: application/json
  • For form data: Content-Type: application/x-www-form-urlencoded
  • For file uploads: Content-Type: multipart/form-data
• Make 100% sure the Content-Type matches the structure of your request body (don't send JSON with a form data header, for example).

2. Validate your request body matches the Content-Type #

Even with the right header, a malformed body can trigger a 415 error. Let's rule this out:

• Compare the request body you're using in Visual Studio to the working request you captured in Fiddler. Check for typos, missing quotes, invalid commas (for JSON), or incorrect key-value pairs (for form data).
• If you're using parameterization in your test, verify that variables aren't inserting invalid characters or breaking the body's structure.

3. Check if Visual Studio is silently modifying your request #

Visual Studio's load test tools sometimes have hidden settings that alter headers or body encoding without you noticing. Try these checks:

• Disable any "auto-encode" or "auto-format" options for the request body in the settings.
• Toggle off settings like "Follow redirects" or "Auto-handle content types"—these can sometimes override your custom headers.
• Use Fiddler to capture the actual request sent by Visual Studio (not just the one you copied manually) and compare it side-by-side with your working Fiddler request. Look for differences in headers (especially Content-Type) or body encoding.

4. Verify the API accepts your media type #

Double-check the API's documentation to confirm which Content-Type values it supports. Some APIs are strict—for example, they might only accept application/json and reject text/plain or form data. If you're unsure, test different Content-Types directly in Fiddler to find the one that works, then replicate that exact setup in Visual Studio.

5. Fix encoding mismatches #

APIs usually expect request bodies to be UTF-8 encoded, but Visual Studio might default to a different encoding. Head to your request's settings, find the Encoding dropdown, and set it to UTF-8 if it's not already selected.

内容的提问来源于stack exchange，提问作者Muhammad Saad