Fix Cursor AI Connection Failed: Ultimate Clash Troubleshooting Guide

Why Cursor AI Connections Fail with Proxies

Cursor AI is built on top of VS Code, but it handles network requests differently. While VS Code primarily uses the system proxy for extension updates, Cursor's AI features (Chat and Composer) communicate directly with backend servers using high-performance protocols like gRPC and HTTP/2. These requests often bypass standard system proxy settings, leading to the dreaded "Connection Failed" message.

Furthermore, many users live in regions where AI services are restricted. In these cases, a simple "System Proxy" toggle in Clash is often not enough because Cursor's underlying Electron process might not respect the environment variables. To solve this, we need a transparent proxy approach that captures all traffic at the kernel level.

Solution 1: Enable Clash TUN Mode (Recommended)

TUN mode is the most robust way to fix Cursor AI issues. It creates a virtual network interface that intercepts all traffic from your computer, ensuring that even processes that ignore proxy settings are routed through Clash.

How to Enable TUN Mode in Clash Verge/Meta:

Install Service Mode: Go to Settings and ensure the "Service Mode" is installed and active (shield icon should be green).
Toggle TUN Mode: Switch the "TUN Mode" toggle to ON.
Select Stack: Use system or gvisor stack (gvisor is generally more compatible for AI tools).

By using TUN mode, Cursor AI will treat the proxy as a direct physical connection, effectively bypassing any internal proxy-handling bugs within the Electron framework.

Solution 2: Adding Specific Proxy Rules for Cursor

Even with TUN mode enabled, you must ensure your Clash configuration is routing Cursor's domains to a proxy group that actually supports AI services (like a US or Singapore node). Many default rule sets categorize Cursor as "Direct" or "General," which might be blocked.

Add the following rules to your Clash configuration (under the rules: section):

- DOMAIN-SUFFIX,cursor.sh,Proxy
- DOMAIN-SUFFIX,cursor.com,Proxy
- DOMAIN-SUFFIX,cursor.ai,Proxy
- DOMAIN-KEYWORD,cursor-ai,Proxy
- DOMAIN-SUFFIX,algolia.net,Proxy
- DOMAIN-SUFFIX,stripe.com,Proxy

Pro Tip: Check Your Node

Cursor AI uses OpenAI and Anthropic under the hood. If your proxy node is from a blocked region (like Hong Kong or Russia), Cursor will still fail even if the connection is "successful." Always use a premium node from a supported region.

Common Error Codes Explained

When Cursor fails, it often provides a small hint in the logs. Here is what they usually mean:

ETIMEDOUT: Your proxy is too slow or the domain is being blackholed by your ISP. Check your TUN settings.
ECONNRESET: The connection was forcibly closed. This often happens if you are using an old version of Clash that doesn't handle HTTP/2 properly.
403 Forbidden: Your proxy IP has been flagged by Cursor's security (Cloudflare). Try switching to a different node.

Addressing DNS Leaks

A "DNS Leak" occurs when your computer asks your local ISP for the IP address of cursor.sh before sending the traffic to Clash. This can result in a failed connection because the ISP returns a fake IP. In Clash, ensure your DNS settings are configured as follows:

dns:
  enable: true
  enhanced-mode: fake-ip
  nameserver:
    - 1.1.1.1
    - 8.8.8.8

Advanced Troubleshooting: Environment Variables

If TUN mode is not an option for you, you can try forcing Cursor to use the proxy via environment variables. Create a shortcut for Cursor and modify the target or launch it from a terminal with these variables:

Experimental Method

This method is less reliable than TUN mode but works for some corporate environments where virtual network adapters are restricted.

export http_proxy=http://127.0.0.1:7890
export https_proxy=http://127.0.0.1:7890
cursor .

Frequently Asked Questions

Does Cursor AI work with Global mode?

Yes, Global mode will usually fix the issue, but it will also slow down your local internet traffic. It is better to use Rule mode with the specific domains listed above.

I enabled TUN mode but it still fails?

Check if you have other VPNs or network accelerators running. They can conflict with the Clash virtual network adapter. Also, restart Cursor after enabling TUN mode.

If you found this guide helpful, check out our other troubleshooting articles: 《Fix Clash Connected but No Internet》 and 《Using Clash TUN Mode for Gaming and AI》.

Summary

Enable TUN Mode in your Clash client to ensure all Electron traffic is captured.
Add cursor.sh and cursor.ai to your proxy rule list.
Ensure you are using a high-quality node from a region supported by OpenAI/Anthropic.
Restart Cursor AI to clear any cached connection failures.

Don't let network issues slow down your coding workflow. Most AI tools in 2026 require a stable, transparent proxy environment to function correctly. While Cursor AI is an incredible productivity booster, its reliance on specific cloud backends makes a robust proxy setup essential.

If you are still using outdated proxy tools that don't support modern TUN stacks or gRPC, you will continue to face these interruptions. Clash provides the most reliable engine for developers working with AI. Download Clash for free and experience seamless AI coding.