Get an OpenAI API key

OpenAI builds the GPT and o-series models. You need an OpenAI Platform account (separate from a ChatGPT Plus subscription) to get an API key.

Create your key

1. 1
   Sign up at platform.openai.com

   Go to platform.openai.com and click Sign up. You can use email, Google, Microsoft, or Apple. Verify your email and complete phone verification if prompted.
2. 2
   Add billing and load credits

   Navigate to Settings > Billing and add a payment method. OpenAI is prepaid -- you must load at least $5 in credits before API calls work. The original free-credit program for new accounts was discontinued in mid-2025.
3. 3
   Create an API key

   Go to Settings > API Keys (direct link: platform.openai.com/api-keys). Click Create new secret key, optionally name it "Prompt Assay", and click Create secret key.
4. 4
   Copy immediately

   The key is displayed only once. Copy it now. If you lose it, delete it and create a new one. Current keys start with sk-proj-.

Add it to Prompt Assay

Open Workspace Settings > Provider Keys, select OpenAI, paste the key, click Test, then Save. See Adding and testing a provider key for the full walkthrough.

Good to know

• A ChatGPT Plus subscription ($20/month) is completely separate from API access. It gives no API credits, and API credits give no chat subscription. They are independent products with independent billing.
• OpenAI billing is prepaid. When your credit balance hits zero, API calls fail. Enable auto-reload in billing settings to avoid interruptions.
• All new keys use the project-scoped format (sk-proj-...). These work correctly with Prompt Assay.
• Rate limits increase automatically as your cumulative spend grows.