The 'Invalid API key for Cursor AI' error means Cursor cannot authenticate with the AI model provider. In 80% of cases, invisible whitespace or newline characters were copied with the key. Paste your API key into a plain text editor first to strip hidden characters, then re-enter it in Cursor settings. Also verify the key has not been revoked or expired.
What does "Invalid API key for Cursor AI" mean?
When Cursor displays "Invalid API key" in a red notification box, it means the API key you provided cannot be authenticated with the model provider. Cursor uses API keys to connect to AI services like OpenAI, Anthropic, or its own backend. If the key is wrong, expired, or contains hidden characters, every AI feature in Cursor stops working — tab completion, chat, and Composer all fail.
This error affects both users who bring their own API keys (BYOK) and those using Cursor's built-in Pro subscription. For Pro users, the error indicates a problem with Cursor's internal authentication rather than a user-provided key. For BYOK users, the key itself is usually the issue.
The most common cause — responsible for roughly 80% of cases — is invisible whitespace. When you copy an API key from a web dashboard, password manager, or email, trailing spaces, newline characters, or zero-width Unicode characters often come along. These are invisible in most input fields but cause the key to fail authentication.
Common causes
Invisible whitespace, newline characters, or
zero-width Unicode characters were copied along with the API key
The API key was revoked, rotated, or
expired on the provider's dashboard (OpenAI, Anthropic, or Azure)
The wrong API key type was entered
for example, an OpenAI key in the Anthropic field or a project key instead of a user key
Cursor's internal authentication token expired or
became corrupted, requiring a sign-out and sign-in
A VPN or corporate proxy is
intercepting the authentication request and modifying the API key header
The API key belongs to an organization or
project that has been deleted or has exceeded its billing quota
How to fix "Invalid API key for Cursor AI" in Cursor
First, strip any hidden characters from your API key. Open a plain text editor like Notepad (Windows) or TextEdit in plain text mode (macOS). Paste your API key there, visually confirm it looks correct with no extra spaces before or after, then copy it again from the plain text editor.
In Cursor, go to Settings (Cmd+, on macOS, Ctrl+, on Windows) and search for "API key." Clear the existing key field completely, then paste the cleaned key. Restart Cursor after saving.
If you are a Cursor Pro user and not using a custom API key, the issue is with Cursor's own authentication. Try signing out of Cursor (Settings > Account > Sign Out) and signing back in. If that fails, check Cursor's status page for any ongoing service disruptions.
For BYOK users, verify your key is still active by testing it directly. For OpenAI: visit platform.openai.com/api-keys and confirm the key is listed and not revoked. For Anthropic: visit console.anthropic.com and check the key status. Make sure your account has billing configured and is not over quota — an active-looking key from an account with no payment method will still fail.
If the error persists, check whether a VPN or proxy is modifying request headers. Try disconnecting the VPN temporarily. Also check that you are entering the key in the correct provider field — Cursor has separate fields for different AI providers.
Prevention tips
- Always paste API keys into a plain text editor first to strip invisible characters, then copy from there into Cursor settings
- Test your API key directly with a curl command or the provider's web playground before entering it into Cursor to confirm it works
- Set a calendar reminder to rotate API keys before they expire, and immediately update them in all tools where they are used
- If using Cursor Pro (not BYOK), try signing out and back in to refresh the internal authentication token before troubleshooting further
Still stuck?
Copy one of these prompts to get a personalized, step-by-step explanation.
I'm getting 'Invalid API key' in Cursor AI editor. I've copied my OpenAI API key from the dashboard and pasted it into Cursor settings. The key works when I test it with curl. What could cause Cursor to reject a valid API key?
Cursor shows 'Invalid API key' after I enter my API key in settings. I've tried re-entering the key multiple times. Walk me through every possible cause and fix, including checking for invisible characters, verifying key type, and testing authentication.
Frequently asked questions
Why does Cursor show "Invalid API key for Cursor AI" even though my key is correct?
In 80% of cases, invisible characters (spaces, newlines, zero-width Unicode) were copied along with the key. Paste the key into a plain text editor like Notepad to strip hidden characters, then copy it again and paste into Cursor. Also verify the key has not been revoked on the provider's dashboard.
How do I test if my API key works outside of Cursor?
For OpenAI, run: curl https://api.openai.com/v1/models -H 'Authorization: Bearer YOUR_KEY'. For Anthropic, run: curl https://api.anthropic.com/v1/messages -H 'x-api-key: YOUR_KEY' -H 'anthropic-version: 2023-06-01'. If these return a valid response, the key works and the issue is with how Cursor is reading it.
Do I need a paid API account for Cursor to work with my own key?
Yes. API keys from accounts without billing configured (free-tier-only accounts) will fail even if the key appears valid. You need an active payment method and sufficient credits on your OpenAI or Anthropic account for the key to authenticate successfully.
Can a VPN cause the invalid API key error in Cursor?
Yes. Some VPNs and corporate proxies modify HTTP headers, which can corrupt or strip the API key from the request. Try disconnecting your VPN and testing again. If the error resolves, configure your VPN to exclude Cursor's traffic.
What is the difference between Cursor Pro authentication and BYOK API key errors?
Cursor Pro users authenticate through Cursor's own system — if this fails, sign out and back in. BYOK (Bring Your Own Key) users provide their own OpenAI or Anthropic keys — if these fail, the key itself is usually the issue. The fix differs based on which authentication method you use.
Can RapidDev help with recurring Cursor API key issues?
Yes. RapidDev can help configure your development environment with secure API key management, proper proxy settings, and automated key rotation to prevent authentication failures. This is especially useful for teams working behind corporate firewalls.
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