A smart contract is a program deployed on a chain that anyone can call and no one can unilaterally change: the ledger executes it exactly as written. Token contracts, swap pools, and invoicing escrows are all smart contracts.
Immutability is the double edge: the rules cannot be bent for anyone, including to fix a mistake. Upgradeable patterns exist but reintroduce someone who can bend the rules; the tradeoff is the discipline of the field.
A smart contract is a program deployed on a chain that anyone can call and no one can unilaterally rewrite. Every node executes it identically and rejects anything else, so the rules are enforced by the network itself. Token contracts, swap pools, checkout escrows, and name registries are all programs in this sense.
Immutability is the defining property and the double edge. The rules cannot be bent for anyone, including to fix a bug. Upgradeable patterns exist, delegating logic to replaceable code, but they reintroduce a party who can change the rules, which is a trust assumption to price. The spectrum from immutable to upgradeable is really a spectrum of who you trust.
Reading a contract before using it is the discipline the environment rewards: verified source on the explorer, a long transaction history, and named audits are the practical signals. Code that holds value and cannot be inspected deserves the suspicion it gets.
A USD token's contract carries its transfer and mint logic; the explorer shows verified source and millions of prior transactions. A checkout escrow contract holds an order's state until its conditions resolve, with no operator able to intercede.
Every UCASH deployment, tokenized asset, and checkout flow on U.CASH is a smart contract you interact with from your own wallet: the contracts' addresses are listed on each asset page.
Every payment flow a merchant touches on U.CASH resolves to contracts: the assets, the routing, the checkout state. Non-custodial is a contract property here, not a policy: the code paths that move your money require your signature, verifiable on the explorer. For the merchant's mental model: contracts are the jurisdiction. The rules that govern a payment are not the platform's terms of service alone but the code paths that execute it, and those are public. U.CASH links contract addresses on asset pages so the jurisdiction can be read directly rather than taken on description.
Every term behind the rails, the assets, and the settlement.