Environment Variables

ETHERSCAN_API_KEY="your_api_key"
ETHERSCAN_RATE_LIMIT="4"

• ETHERSCAN_API_KEY — required for every method except usage.chain_list. Read by Etherscan.new() when api_key isn't passed directly. See API keys setup.
• ETHERSCAN_RATE_LIMIT — optional client-side cap on calls per second. Read by Etherscan.new() when rate_limit isn't passed directly; unset means no client-side cap, only Etherscan's own reactive one.

Both are only ever read from the environment, never from any other source, and only inside Etherscan.new().