Understanding Cursor AI Networking

Cursor AI is not just another text editor; it is a fork of VS Code deeply integrated with Large Language Models (LLMs) like Claude 3.5 Sonnet and GPT-4o. Unlike standard editors that primarily handle local files, Cursor maintains constant, high-frequency connections to multiple backend services. These include authentication servers, telemetry endpoints, and, most importantly, the inference APIs that power its AI features.

In 2026, Cursor has moved toward a more distributed architecture. It uses gRPC and long-lived WebSocket connections to ensure low-latency code completions. When you use Clash, these specific protocols can sometimes be misrouted or blocked by aggressive firewall rules, leading to the dreaded "Connection Failed" banner. Understanding that Cursor behaves more like a high-performance cloud application than a local IDE is the first step toward fixing connectivity issues.

ℹ Note: Cursor's AI features often rely on cursor.sh and api.cursor.sh, but also touch Anthropic and OpenAI endpoints directly depending on your settings.

Why Clash Causes "Connection Failed"

The conflict between Clash and Cursor AI usually stems from three main areas: System Proxy limitations, DNS hijacking, and Protocol incompatibility. Most users rely on the standard "System Proxy" mode, which works by setting environment variables or OS-level proxy settings. However, many components of the Cursor/VS Code ecosystem (especially extensions and the internal terminal) do not always honor these settings perfectly.

Furthermore, if your Clash configuration uses a MATCH, DIRECT rule as the final catch-all, and Cursor tries to reach a new or undocumented telemetry endpoint that isn't in your rule list, the connection might be attempted locally. If you are in a region with restricted access to AI services, this "Direct" attempt will time out, causing the editor to report a connection failure.

The most common symptom is that the editor opens fine, but "Cmd+K" or "Chat" features stay in a "Thinking..." state forever before eventually timing out.

Solution 1: Enabling TUN Mode (Recommended)

The most robust way to solve Cursor AI connection issues is to enable TUN Mode in Clash. TUN mode creates a virtual network interface that captures all traffic at the IP layer, ensuring that even applications that ignore system proxy settings (like Cursor's internal networking stack) are correctly routed through your proxy.

To enable TUN mode in your config.yaml, you need to add the following block under the tun: section. Ensure you are using Clash V.CORE or a Mihomo-derived core for the best performance.

Illustrative TUN Mode Configuration

tun:
  enable: true
  stack: mixed # or gvisor
  dns-hijack:
    - "any:53"
    - "tcp://any:53"
  auto-route: true
  auto-detect-interface: true

Once TUN mode is active, Cursor's traffic will be intercepted globally. This eliminates the need for manual proxy configuration within the editor and solves issues where Cursor's background processes bypass the standard system proxy.

Solution 2: Custom Domain Rule Configuration

If you prefer not to use TUN mode, or if you want to ensure Cursor traffic is always routed through your fastest "AI" policy group, you must update your Clash rules. Cursor uses a specific set of domains that must be prioritized.

Add these rules to the top of your rules: section in your Clash configuration file. We recommend creating a dedicated policy group named AI_Services for these.

ℹ Pro Tip: Using DOMAIN-SUFFIX is more efficient than DOMAIN-KEYWORD as it prevents accidental matching of unrelated sites that happen to contain the word "cursor".

Solution 3: Resolving DNS Pollution in Cursor

Even with the right rules, DNS pollution can cause connection failures. If Cursor attempts to resolve api.cursor.sh and receives a poisoned IP address from a local DNS server, Clash might try to route that poisoned IP incorrectly.

To fix this, configure the dns: section in Clash to use Fake-IP mode and reliable upstream DNS servers over TLS or HTTPS (DoT/DoH).

Optimized DNS Config for AI Developers

dns:
  enable: true
  enhanced-mode: fake-ip
  nameserver:
    - https://dns.google/dns-query
    - https://1.1.1.1/dns-query
  fallback:
    - https://8.8.8.8/dns-query
    - tls://1.1.1.1:853

By using fake-ip, Clash returns a dummy IP to Cursor immediately, allowing Clash to handle the actual DNS resolution remotely on the proxy server. This completely bypasses local DNS interference.

Solution 4: Terminal Proxy Environment Variables

Cursor's integrated terminal often behaves differently than the GUI. If you are running commands like npm install or git push inside Cursor and they fail, you may need to explicitly set proxy variables in your shell profile (e.g., .zshrc or .bashrc).

Add the following lines to your shell configuration, replacing 7890 with your actual Clash mixed-port: 

export http_proxy="http://127.0.0.1:7890"
export https_proxy="http://127.0.0.1:7890"
export all_proxy="socks5://127.0.0.1:7890"

After saving, run source ~/.zshrc. This ensures that CLI tools launched from within Cursor can also reach the internet through Clash.

Advanced Mihomo Core Features for Cursor

In 2026, the Mihomo (Clash Meta) core offers advanced features like process-name matching. This allows you to route traffic specifically based on the application name, which is incredibly useful for Cursor.

Instead of relying solely on domains, you can create a rule that catches any traffic originating from the Cursor executable:

This is a "catch-all" for Cursor, ensuring that even telemetry or hidden API calls that you haven't explicitly listed in your domain rules are still routed correctly through your proxy.

⚠ Compliance Reminder: Always ensure you are complying with local laws and the terms of service of your AI providers. This guide is for technical troubleshooting of Clash routing and DNS configurations for authorized accounts.

Summary Checklist & Final Thoughts

If you are still facing issues, run through this quick checklist:

  1. Check if TUN Mode is active and showing traffic in the Clash dashboard.
  2. Verify that api.cursor.sh is matching your AI_Services policy group.
  3. Ensure you don't have a conflicting VPN or another proxy (like a browser extension) running simultaneously.
  4. Restart Cursor completely after making changes to your Clash config.

Connectivity issues should not hinder your productivity with the world's most advanced AI code editor. By leveraging the power of Clash V.CORE and properly configuring your routing rules, you can enjoy a seamless, zero-latency coding experience.

→ Download Clash V.CORE today to experience the most stable and feature-rich proxy core for AI developers. Optimized for Cursor, Claude, and OpenAI workflows.