What is Environment Variable?
A value stored outside your code, like an API key or database URL. Your code reads it at runtime so secrets never get committed to a repository.
read at runtime · not in code
Environment variables keep secrets...
Write it in your own words in the app.
In real work
Store the Claude API key as an environment variable in the secrets folder. Never hardcode it in a tutorial or a public repo.
In the illustration
The cartridge ships with only the name API_KEY on an empty socket; when it starts, a value card slides in from the host's panel outside the code and the run lamp lights.
Add STRIPE_WEBHOOK_SECRET as an environment variable on your deploy platform, set separately for preview and production. Read it only inside the webhook route and never log it.
Try it now
The fastest way to learn a word is to use it. Open this line in the agent you already work in and watch what it does. Change the tool to the one you use.
Go further
01Practice
Make it stick
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02Verify
Prove you know it
Pass the quiz and keep it in a Skills Wallet you can share with anyone who needs proof.
03Career
Find the work that uses it
See which roles lean on this vocabulary, and what they pay in year one.
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