API key
Also called api keys · secret key
A secret string that identifies your account to an AI provider and authorises charges against it.
In more detail
You create an API key inside a provider's console, and any software holding it can make requests that bill your account. It functions as a password with a spending limit attached, which is why providers show it once and why leaking one is a billing problem rather than just a security one.
Example
In the Anthropic console you open API Keys, create a key, and paste it into a tool's config. From then on that tool's requests are charged to your Anthropic balance.
Why it matters
The key is the thing that makes a production stack yours. It is also the thing most worth protecting: a key committed to a public repository or pasted into an untrusted tool can be used by anyone who finds it, at your expense. Most providers let you set spend limits and rotate keys, and both are worth doing before the first large batch run rather than after.