Content Negotiation Errors — Accept Header and 406 Not Acceptable Responses

Overview

Fix HTTP content negotiation errors where servers return 406 Not Acceptable or wrong content formats due to Accept header mismatches.

Key Details

• Content negotiation allows clients to specify preferred response formats using Accept headers
• Accept: application/json requests JSON; Accept: text/html requests HTML; Accept: */* accepts any format
• 406 Not Acceptable is returned when the server cannot produce a response matching the Accept header
• Quality values (q=0.9) indicate preference order: Accept: application/json;q=1, text/html;q=0.5
• Content-Type in the response indicates which format was chosen by the server

Common Causes

• Client sending Accept: application/json to an endpoint that only returns HTML
• Server strictly enforcing Accept headers instead of falling back to a default format
• Accept header malformed — missing commas between media types or invalid quality values
• API documentation specifying a different Accept header than what the server actually expects

Steps

1. 1Set the correct Accept header for the expected response format: application/json for REST APIs, text/html for web pages
2. 2Use Accept: */* or omit the Accept header to accept any format the server provides
3. 3Implement server-side fallback: if no Accept header matches, return the default format instead of 406
4. 4Check the Content-Type of the response to verify which format was selected
5. 5Test content negotiation: 'curl -H "Accept: application/json" https://api.example.com/resource'

Tags

More in 4xx Client Error

Frequently Asked Questions