What Is an API Key, and How Do You Get One?

In short: An API key is a long password that lets a program use a service on your behalf. For AI, it is what you paste into an app, a script or a coding tool so it can send your questions to a model - Gemini, Groq, OpenRouter and others - and count the usage against your account. You get one from the AI provider's website, usually free, in a minute.

What an API is

An API (application programming interface) is a way for one program to ask another for something. When an app sends a question to Gemini and gets an answer back, it does that through Gemini's API. You do not need to know how the AI works; the API takes a request and returns a result.

What an API key is

The provider needs to know who is asking, so it can apply your free limits and, on paid plans, your bill. The API key is how it knows. It is a long string of letters and numbers, such as gsk_... for Groq, sent with every request.

What an API key is used for

• Apps made for OpenAI: chat apps, writing tools and plugins that ask for an "OpenAI API key" accept keys from many other providers too. The settings for each free provider are on the free APIs page.
• Coding apps: tools such as OpenCode use your key to run a model while you code.
• Your own scripts: a few lines of Python or a command in PowerShell can send questions with your key.

How to get an API key for free

Each provider has its own page for keys, and several have a free tier:

The full list, with every provider's limits and the ones that are not free, is on how to get AI API keys for free.

Is a ChatGPT or Claude subscription an API key?

No. A ChatGPT or Claude subscription is for the chat app. API keys are made separately, on the provider's developer site, and the subscription does not come with one. To use AI from a program for free, use a provider with a free API tier from the table above.

How to keep your API key safe

• Treat it like a password. Anyone with your key can use your free allowance, or spend your money on a paid plan.
• Never share it in a chat, a forum post, a screenshot or a public code repository such as GitHub.
• Keep it out of your code. Store it in an environment variable (for example GEMINI_API_KEY) and let the code read it from there.
• One key per app. If one app leaks its key, you delete only that one.
• Delete a leaked key at once on the provider's API keys page, then create a new one.

What the common errors mean

Words to know

• API: how one program asks another for something.
• API key: the password that identifies your program to the API.
• Free tier: the free allowance a provider gives each account.
• Rate limit: how many requests you may send per minute or per day.
• Environment variable: a named value stored on your computer, read by programs, so the key is not written inside the code.
• Token: a piece of a word; the unit models read and write. See tokens and context windows.