Why 415 Unsupported Media Type Happens (and How to Fix It Fast)

A practical problem page for debugging 415 errors with exact header checks and copy-ready fixes.

Most 415 errors are not backend logic bugs. They come from mismatched Content-Type, malformed parameters, or body/header mismatch. This page gives a direct troubleshooting path.

Tools in this guide

CTPContent-Type Parser (MIME, Charset, Boundary)CTGContent-Type Generator (MIME Header Builder)MIMEMIME Type List & Content-Type ReferenceHDRHTTP Headers Parser (Raw Header to JSON)REQHTTP Request Builder

Symptoms

  • API returns HTTP 415 right after request hits server.
  • Same endpoint works in Postman but fails in frontend/client SDK.
  • Multipart upload fails even though file bytes are present.

Root Cause

  • Content-Type header does not match body format (JSON/form-data/text).
  • Header has malformed params, such as invalid charset or missing boundary.
  • Gateway/proxy rewrites Content-Type and drops required parameters.

Fix Steps

  1. Paste raw Content-Type lines into Content-Type Parser and confirm normalized output.
  2. If multipart is used, verify boundary exists and matches body separators.
  3. Regenerate canonical header with Content-Type Generator, then retest request.

Known-good JSON request header

Content-Type: application/json; charset=utf-8
Accept: application/json

Related Tool Workflow

Validate Content-Type lineGenerate canonical headerRebuild and retest request

FAQ

Can 415 happen even when JSON is valid?

Yes. 415 is about media type contract, not JSON syntax only.

Should I set charset for JSON?

Using utf-8 explicitly is a safe default for mixed environments.