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🛡️ Security · ⏱️ 2 min Latte

What is API key?

Illustration: API key
Simply put, like I'm 5 years oldAn API key is like the key to a shared kitchen where every meal you cook goes on your bill. If someone copies your key, they can cook all night, and you pay.

📖 The slightly longer version

An API is a door that lets one program talk to another program. When an app or a coding agent uses a paid AI service, it does not type a username and password like you do. It sends an API key: a long secret string of letters and numbers that says "this is me, charge my account."

Anyone who has the key can use the service as if they were you. That can mean spending your money or reaching your data. This is why developers keep keys out of shared files and change them ("rotate" them) when they think a key has leaked. A coding agent often needs a key to work, so it can see keys, save them, or copy them by mistake.

How an API key works, and how it leaks

  1. Get a keyYou sign up for a paid AI service and it gives you a secret key.
  2. Software uses itYour app or coding agent sends the key with each request.
  3. Service charges youThe service checks the key and puts the cost on your account.
  4. Key gets savedAn agent may write the key into a settings file without you noticing.
  5. File goes publicIf that file is shared online, anyone can copy the key and use it.
Why it matters

This week, Ars Technica reported that Claude Code settings files on public GitHub are exposing "thousands of secrets", including API keys, after Apiiro linked the problem to the "Don't Ask Again" option. A key sitting in a public file is like a house key taped to the front door. If you or your company use AI agents, a leaked key can mean a surprise bill or someone else reading your data.

⚠️ What to watch out for

We do not know how many of these leaked keys were really used by attackers, and the number of affected files comes from one security company's report. Changing a key fixes that key, but it does not fix the habit: agents get deep access by default, and problems are often found after the damage. A sandbox, a sealed box where the agent cannot read the rest of your computer, helps, but it is not a full guarantee.

📰 Where it showed up

This notion came up in A new Claude takes the top spot while trust cracks everywhere else. More lessons: Learn.

🎯 Keep learning

New 🛡️ Security · 2 min Cappuccino What is Formal verification? Testing code is like tasting a soup a few times to see if it is good. Formal verification is like checking every step of the recipe so carefully that you can be sure it is right, without tasting. Learn it → New 🛡️ Security · 2 min Latte What is Penetration Testing? It is like asking a friend to try every door and window of your house, so you find the one that does not lock before a burglar does. Learn it → 🛡️ Security · 2 min Latte What is Privilege Escalation? Imagine a hotel guest whose room key, because of a small mistake, also opens the manager's office and every other room. Privilege escalation is when a computer user finds a mistake like that and gets keys they were never supposed to have. Learn it →

Sources

Written on 2026-11-10. This explanation was accurate on that day. AI changes fast, so check the sources and the date before you rely on it.

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