Cross-chain trading has a hard problem at its core: how do you move value between two ledgers that don't speak to each other, without either side getting cheated and without parking the funds with a third party?

The answer the industry settled on, years before "intent-based DeFi" was a phrase, is the Hash Time-Locked Contract — an HTLC. It's the primitive underneath atomic swaps, the Lightning Network, most cross-chain bridges that don't trust an oracle, and the settlement leg of Hashlock Markets .

This post walks through the HTLC mechanism end-to-end, then shows how Hashlock Markets exposes it as four MCP tools your AI agent can call directly across Ethereum, Bitcoin, and SUI.

1. The two locks

An HTLC is a smart contract (or, on Bitcoin, a script) holding funds behind two conditions:

The hashlock. The contract knows a hash H = sha256(s) . The funds release to the receiver if and only if the receiver presents the 32-byte preimage s .…