Fix Claude AI Error 400 Bad Request Parameter Invalid (2025)

Updated: 11/29/2025

You try to chat or run a process in Claude AI, hit submit, and instantly get Error 400 Bad Request or a warning about an invalid parameter. The session gets stuck, but other sites work fine. This usually means there’s a formatting problem in your request, a browser or extension glitch, or a temporary mismatch in how Claude reads the input you sent.

Table of Contents

Method 1: Review Request Formatting And Input Length

Start a new Claude chat or conversation and send a very simple message like ‘Hello’ or ‘Test’. If it works, you know the previous input triggered the error due to length or formatting.

Method 2: Clear Browser Cookies, Extensions, And API Keys

If using the API, reset your Claude key in the developer console and update your app or integration. Old API keys can expire or lose access with backend updates.

Note: Restart your browser after making changes to fully clear corrupted states.

Method 3: Reset Network Settings And Try Different Devices

If you’re comfortable, on Windows open Command Prompt with admin rights and run:

ipconfig /flushdns

This refreshes network routing and clears hidden connection issues with Claude.ai.