Before ERC-20, every token invented its own interface and every wallet needed bespoke support. The standard fixed a handful of functions and events — transfer, approve, balanceOf — and an ecosystem formed: any conforming token is listable, swappable and walletable on day one.
The sharp edge is 'approve': it lets another contract spend from your balance, up to the amount you allow — and unlimited approvals, granted once and forgotten, are how most drained wallets are drained. 'Revoke what you no longer use' is basic wallet hygiene, the way revoking API keys is.
Related terms
ERC-721
The Ethereum standard for non-fungible tokens: a contract interface where every token has its own distinct identity and owner.
Smart contract
A program deployed to a blockchain that runs exactly as written, that anyone can call, and that usually cannot be changed afterwards.
SPL token
Solana's token standard — the shared program every fungible and non-fungible token on the chain uses, so wallets and apps speak one format.
The bench this belongs to
BlockchainSolidity on Ethereum, Polygon, Base and Arbitrum. Anchor programs on Solana. Written with tests first, because a redeploy is not a hotfix once value is on the line.
