Cursor Error Troubleshooting Guide: 10+ Solutions for API Key, Model, Network Issues

It was 1 AM, and I was coding away in Cursor — the AI autocomplete was so good I felt like a legendary 10x developer. Suddenly, a red error box popped up in the bottom right: Invalid API Key.

I froze for three seconds. What the hell? It was working fine yesterday.

I opened settings and checked — the API Key was right there. Copied and pasted it again, still got the error. Restarted Cursor, same thing. At 1:30 AM, staring at that error message, I had only one thought: help, I haven’t finished the feature that’s supposed to go live tomorrow.

Railway - Modern deployment platform, zero-config, go live in minutes

Start Now →Ad

Turns out, when I copied the key, I accidentally included a newline character at the end. Just one invisible character wasted half an hour of my time.

Honestly, in my time using Cursor, I’ve encountered at least a dozen different errors: expired APIs, failed network connections, Tab completion suddenly stopping, chat history mysteriously disappearing… Each time I had to search online, read docs, try different solutions. Sometimes the problem was simple, but I just couldn’t find the right fix. Other times the error messages were all in English and completely confusing.

So I put together this “Cursor Error Quick Reference Guide.” 10+ of the most common problems, each with specific solution steps. When you hit an error, just check this guide and you’ll usually fix it within 5 minutes.

Quick Diagnosis - 4 Steps to Identify 80% of Problems

Don’t panic when you hit an error. Most issues can be quickly identified through these 4 steps.

Step 1: Look for Keywords in the Error Message

Error messages usually contain keywords that point directly to the problem type:

• Contains API, Key, Invalid → API configuration issue
• Contains Network, Connection, Timeout → Network issue
• Contains Model, Unsupported → Model selection issue
• Contains Permission, Access → Permission or subscription issue

For example, if the message says Network timeout, it’s basically a network thing — no need to mess with your API Key.

Step 2: Check if Network is Connected

Cursor’s servers are overseas, so network issues are the most common culprit. Quick check method:

• Open your browser and visit https://api2.cursor.sh
• If it opens (even if it shows 404 or another page) → network is connected
• If it doesn’t open or keeps spinning → network problem

If it’s a network issue, try switching DNS, using a proxy, or switching to HTTP/1.1 mode (details below).

Step 3: Check the Cursor Status Bar

The status bar in the bottom right corner of Cursor shows the current state. If you see:

• Red exclamation mark → an error occurred
• Spinning icon keeps spinning → might be stuck, network or server issue
• Shows “Offline” or “Disconnected” → you’re disconnected

Click the status bar icon to usually see more detailed error information.

Step 4: Open Developer Tools to Check Logs

This is the “killer move” for when the first three steps didn’t find the problem.

Method: Help → Toggle Developer Tools (or press Ctrl+Shift+I / Cmd+Option+I)

After opening, switch to the Console tab and look for red errors. These logs usually tell you more specific error reasons. While they’re in English, you can usually understand the keywords. If not, just copy the error message and search for it online.

API and Model Related Errors

Invalid API Key

What It Looks Like

Pop-up shows Invalid API Key or API key not found, chat function completely stops working.

Why This Happens

I’ve encountered three situations:

1. Extra spaces or newlines during copy — this is the worst because you can’t see it at all. That’s how I got burned — there was a newline character at the end of the key. Visually identical, but just wrong.

2. Key expired or revoked — if you’re using a key from OpenAI or another platform, it might be account arrears, key deletion, or hitting usage limits.

3. Wrong key type — for example, you configured an OpenAI Provider but pasted an Azure key. They’re both strings of characters, but the format is different.

How to Fix It

Try the simple stuff first:

1. Copy the key again, note: after copying, paste it into Notepad first to check for extra spaces or newlines, confirm it’s clean before pasting into Cursor
2. Configuration path: Settings → Cursor Settings → Models → Add API Key
3. Remember to press Enter or click save after pasting

Still not working? It might be the key itself:

• Go to your API platform (OpenAI, Claude, etc.) and check the key status, see if it’s disabled or deleted
• Confirm your account balance is sufficient — some platforms will invalidate keys when balance is low
• Try generating a new key

Finally, confirm that your chosen Provider matches the key. If you’re using a Claude key, the Provider should be Anthropic. If it’s an OpenAI key, choose OpenAI. Don’t mix them up.

Model Not Supported

What It Looks Like

Shows Model not available or Unsupported model, the model you selected won’t work.

Why This Happens

Usually one of these possibilities:

1. Model not in your subscription — for example, you’re on the free tier but selected GPT-4 or Claude Opus, that definitely won’t work. Free tier has limited models available.

2. Model name typo — if you manually entered the model name (though generally not recommended), one wrong letter and it won’t work.

3. Model deprecated or renamed — AI models update quickly, some old models get replaced by new versions. For example, versioned ones like gpt-3.5-turbo-0301 might no longer be supported.

How to Fix It

The safest approach: use the dropdown menu, don’t type manually.

1. In the chat interface or settings, click the model selection box
2. Choose from the dropdown list — everything in the list is currently available
3. If the model you want isn’t in the list, your subscription level isn’t high enough

If you’re on Pro but a model still shows as unsupported:

• Check if Cursor has updates: go to Help → Check for Updates
• Check the official changelog to confirm if this model is still on the support list
• Some new models might need a few days to sync to Cursor

Honestly, when you hit this problem, the fastest solution is just to switch models. GPT-4 not working? Try Claude. Claude not working? Use GPT-3.5. There’s always one that works.

Request Timeout

What It Looks Like

Waited forever, then finally got Request timeout or Connection timeout. Your question was sent, but AI didn’t respond.

Why This Happens

Timeout is usually one of these three reasons:

1. Unstable network — high latency, packet loss, or network fluctuations preventing requests from being sent or responses received.

2. Your request is too long — selected thousands of lines of code for AI to analyze at once, or chat context is particularly long. Model takes a while to process, easy to timeout.

3. Server too busy — during peak hours, Cursor’s servers might respond slowly. You can’t control this.

How to Fix It

First check if it’s a network issue:

• Try accessing other websites to see how your connection is
• If using a proxy, switch nodes or change proxies
• Refer to the network diagnosis methods mentioned earlier

If network is fine, reduce request size:

• Don’t select too much code at once, break it into multiple questions
• Clear chat history, start a new conversation (old conversations being too long slows things down)
• Try a smaller model, like switching from GPT-4 to GPT-3.5, response will be much faster

If nothing works, just wait and try again. Sometimes the server is just busy — try the same request 10 minutes later and it might work.

Network Connection Errors

Connection Failed

What It Looks Like

Shows Connection failed, Network error, or just spins forever then times out.

Why This Happens

Cursor’s servers are overseas, so network issues are super common. I’ve encountered this several times before — other websites work fine, but Cursor just won’t connect.

When troubleshooting, try these directions:

Direction 1: DNS Issue

Sometimes it’s a DNS resolution problem. Switching DNS servers might fix it.

• Windows: Open network settings, change DNS to 8.8.8.8 (Google) or 1.1.1.1 (Cloudflare)
• macOS: System Settings → Network → Advanced → DNS, add the above addresses

Direction 2: Proxy Settings

If you’re using a proxy:

• Confirm proxy software is running normally
• Try switching to different nodes
• Check if the proxy supports the api2.cursor.sh domain

If you’re not using a proxy but your company has a corporate proxy, you might need to configure Cursor’s proxy settings (search for “proxy” in Settings).

Vultr - High-performance NVMe VPS with 32 global locations, one-click Docker deploy

View Pricing →Ad

Direction 3: HTTP/1.1 Mode

This is one of the most effective methods I’ve tried. Cursor uses HTTP/2 by default, but some network environments don’t support HTTP/2 well.

How to switch:

1. Open Cursor settings (Settings)
2. Search for http
3. Find the Cursor: Use HTTP/1.1 option and check it
4. Restart Cursor

This method has solved at least 3 connection failures for me. Not sure why, but it really works.

Direction 4: Firewall and Antivirus

Some firewalls or antivirus software will block Cursor’s network requests. Try:

• Temporarily disable firewall or antivirus to see if you can connect
• If yes, add Cursor to the whitelist

SSL/TLS Certificate Error

What It Looks Like

Shows something like SSL certificate problem or Certificate verification failed.

Why This Happens

This problem usually appears in corporate network environments.

Many companies use enterprise proxies to do SSL inspection (aka “man-in-the-middle attack,” but this time it’s the company doing it). The proxy replaces Cursor’s certificate, causing verification to fail.

How to Fix It

Honestly, you can’t really fix this yourself — you need to contact IT:

• Have them add api2.cursor.sh and *.cursor.sh to the SSL inspection whitelist
• Or have them install the company’s root certificate on your computer

If you’re a personal user encountering this, it might be incorrect system time (certificate verification checks time) — confirm your system time is accurate.

Feature Failure Issues

Tab Completion Not Working

What It Looks Like

Tab key does nothing, or after pressing shows Tab completion quota exceeded.

Why This Happens

Tab completion not working is usually one of these reasons:

1. Free quota used up — free tier only has 2000 Tab completions, once they’re gone, they’re gone. Note this quota does not reset — it’s not 2000 per month, it’s 2000 total.

2. Feature disabled — might be accidental user action or some setting conflict.

3. Input method conflict — this is pretty hidden. Some Chinese input methods intercept the Tab key, preventing Cursor from receiving the key event.

How to Fix It

Check quota first:

• See if the Cursor status bar shows remaining completions
• If quota is exhausted, either upgrade to Pro ($20/month, unlimited) or just use chat features

Check settings:

1. Open Settings, search for tab
2. Confirm Cursor Tab feature is enabled
3. Check for shortcut conflicts (other extensions using the Tab key)

Input method issue:

• Switch to English input method and try again
• Or release the Tab key in your input method settings

If still not working, try restarting Cursor. Sometimes it just gets stuck inexplicably and restart fixes it.

Lost Chat History

What It Looks Like

Previous conversations suddenly can’t be found, chat panel is completely empty.

Why This Happens

I’ve lost chat history twice — once was reinstalling Cursor without backing up, once was insufficient disk space causing data to be cleared.

Common causes:

1. Insufficient disk space — Cursor stores chat history locally, full disk might trigger automatic cleanup
2. Reinstalling or updating Cursor — if you didn’t back up data, chat history might be lost after reinstalling
3. Switching workspace — Cursor’s chat history is stored by workspace, changing project folders means you can’t see previous records

How to Fix It

First see if you can recover it:

• Windows users: go to %APPDATA%\Cursor\User\workspaceStorage and check for backups
• macOS users: go to ~/Library/Application Support/Cursor/User/workspaceStorage and look

Each workspace has an independent folder storing conversation records. If the files are still there but Cursor isn’t reading them, try restarting.

Prevention measures:

• Keep at least 10GB of disk space, don’t let the system auto-clean files
• Regularly export important conversations (copy-paste to note-taking software)
• Back up the workspaceStorage folder before reinstalling

Honestly, Cursor doesn’t do great on data backup. For important conversations, manually save a copy — don’t completely rely on local storage.

Agent Mode Unavailable

What It Looks Like

Agent button is grayed out, or clicking it does nothing, shows Agent mode unavailable.

Alibaba Cloud - Top choice for developers, exclusive 15% off for Lighthouse servers

Get 15% Discount →Ad

Why This Happens

Agent mode has high requirements for network and subscription:

1. Unstable network — Agent needs sustained stable connection, network fluctuations will make the feature unavailable
2. Insufficient subscription level — free tier might not have Agent feature, or has usage limits
3. HTTP/2 protocol issue — similar to the network issues mentioned earlier, HTTP/2 is unstable in some environments

How to Fix It

First confirm subscription status:

• Check if you’re a Pro user
• Check if subscription has expired

Then check network:

• Refer to the network diagnosis methods mentioned earlier
• Switch to HTTP/1.1 mode (this is really useful)
• If using a proxy, try changing nodes

Finally, restart works wonders. Agent mode sometimes gets stuck, restarting Cursor usually solves it.

Installation and Subscription Issues

Installation Failed / Update Failed

What It Looks Like

Installer gets stuck, errors out, or won’t launch after installation completes. Update shows Update failed or gets stuck on the update screen.

Why This Happens

Installation and update failures are usually one of these reasons:

1. Insufficient permissions — especially on Windows, lack of admin rights can cause installation to fail
2. Insufficient disk space — Cursor needs at least 2-3GB of installation space, full disk will fail
3. Antivirus blocking — some antivirus software treats Cursor’s installer as suspicious

How to Fix It

Try the simplest first:

1. Run as administrator (Windows): right-click the installer, select “Run as administrator”
2. Clear disk space: ensure at least 5GB is available
3. Temporarily disable antivirus: turn off antivirus temporarily, turn it back on after installation

If still not working:

• Download the latest installer (the previous download might be corrupted)
• Completely uninstall the old version then reinstall
• Check system logs for specific error messages

For update failures:

• Try manually downloading the new version installer and doing an overlay installation
• Or wait a few hours and try again (sometimes it’s Cursor’s update server being busy)

Pro Subscription Not Taking Effect

What It Looks Like

Paid for Pro version, but Cursor still shows free tier limitations, like Tab completion quota hasn’t become unlimited.

Why This Happens

This problem is pretty common, usually sync delay:

1. Account sync takes time — after payment completes, Cursor’s servers might need 10-15 minutes to sync subscription status
2. Wrong account logged in — if you use multiple accounts, you might have logged into the wrong one
3. Cache issue — Cursor has cached old subscription information locally

How to Fix It

Try the most effective method first:

1. Sign out completely (Settings → Sign Out)
2. Sign back in (confirm you’re using the account that purchased Pro)
3. Restart Cursor

If still not working:

• Wait 10-15 minutes then check again (it really might just be slow sync)
• Go to Cursor’s website account page to check subscription status, confirm payment succeeded
• Check your email for confirmation email

If nothing works, contact support:

• Email [email protected]
• Provide your order number and login email
• Usually resolved within a few hours

Marketplace Inaccessible

What It Looks Like

When opening the Extensions marketplace, it keeps loading or shows Unable to connect to marketplace.

Why This Happens

The marketplace server is in a different location than the main program, network restrictions might prevent access. Especially in certain regions or corporate network environments.

How to Fix It

Method 1: Check network

Railway - Modern deployment platform, zero-config, go live in minutes

Start Now →Ad

• Confirm you can access other websites
• Try enabling proxy or changing nodes

Method 2: Modify configuration (advanced users)

• Find Cursor’s product.json file
• Modify extensionsGallery configuration to use domestic mirrors
• Note: This method has some risk, for learning reference only

Method 3: Manually install extensions

• Download .vsix files from VS Code marketplace
• In Cursor, select “Install from VSIX” to manually install

Honestly, if this problem is due to network reasons, there’s no great solution besides using a proxy. But fortunately Cursor’s built-in features are already very powerful — extensions aren’t necessary.

Performance and Resource Issues

Cursor Using Too Much Memory

What It Looks Like

After Cursor runs for a while, Task Manager shows it using several GB of memory, computer becomes very slow.

Why This Happens

High memory usage is usually one of these reasons:

1. Large project indexing — Cursor indexes the entire project’s code, larger projects use more
2. Too many extensions — each extension uses some memory, too many accumulates
3. Memory leak — not restarting for a long time, some features might cause memory leaks

How to Fix It

Limit indexing scope:

1. Create a .cursorignore file in the project root
2. Add directories that don’t need indexing, like node_modules, dist, .git
3. Example:

node_modules/
dist/
build/
.git/
*.log

Disable unnecessary extensions:

• Open Extensions, disable extensions you’re not currently using
• Especially those that analyze code in real-time

Increase Node.js memory limit (advanced):

• Add --max-old-space-size=4096 to startup parameters
• But this only treats symptoms not the root cause, the real solution is to reduce memory usage

Simplest method: restart Cursor periodically. I usually restart once a day, keeps memory usage in a reasonable range.

Slow Response Speed

What It Looks Like

AI replies very slowly, typing has delays, overall feels sluggish.

Why This Happens

Slow response is usually one of these reasons:

1. Network latency — slow connection to Cursor servers, every request takes forever
2. High server load — during peak hours when everyone’s using it, server responds slowly
3. Context too long — chat history is very long, each request has to send lots of context

How to Fix It

Optimize network:

• Check network latency (ping api2.cursor.sh)
• If using proxy, switch to a faster node
• Refer to the network optimization methods mentioned earlier

Switch to faster models:

• GPT-3.5 is much faster than GPT-4
• Claude Haiku is faster than Claude Opus
• For simple tasks, small models are good enough

Reduce context length:

• Start new conversations periodically, don’t let chat history get too long
• When selecting code, don’t select too much — just enough
• Clear unrelated file references

If it’s slow due to peak hours, you just have to wait. Usually evenings or weekends are better.

Summary: Cursor Error Quick Checklist

When you encounter a problem, quickly troubleshoot using this checklist:

Step 1: Basic Checks

• Check error message keywords to identify problem type
• Test network connectivity (visit api2.cursor.sh)
• Check Cursor status bar notifications
• Open developer tools to check console logs

Step 2: Common Issues Quick Reference

• Invalid API Key → Check for spaces/newlines, verify key validity
• Connection failed → Switch to HTTP/1.1, check proxy and DNS
• Tab not working → Check quota, check input method
• Model not supported → Use dropdown menu to select, check subscription
• Lost chat history → Check workspaceStorage directory

Step 3: Advanced Troubleshooting

• Disable extensions for testing (rule out extension conflicts)
• Clear cache and configuration
• Reinstall Cursor (after backing up data)
• Check Cursor official status page
• Contact official support

Remember: 80% of problems can be solved within 5 minutes through the first two steps. Try the simple stuff first, then the complex.

Don’t panic when you hit a problem — check through this list item by item. If you really can’t solve it, remember to back up your data, then go to the official forum or community for help — someone else has probably encountered the same issue.

Bookmark this article, and you’ll know what to do next time Cursor throws an error.

18 min read · Published on: Jan 19, 2026 · Modified on: Feb 4, 2026

Easton

Technology