Get an OpenAI API key

Sign up for the OpenAI Platform, add billing, create an API key, and copy it into Prompt Assay.

Updated 2026-04-16

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. 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. 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. 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. 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.