Explainer · 3 min read
What Is an Atomic Swap? How Trustless Crypto Swaps Work
An atomic swap trades one cryptocurrency for another with no exchange holding the coins. How it works, what it protects you from, what it costs, and where to do one.
Updated · First published 13 Oct 2026
An atomic swap is a trade between two people on two different blockchains in which either both transfers happen or neither does. No exchange, escrow agent or bridge holds the coins in between. The word “atomic” is borrowed from databases, where it means an operation cannot be left half finished.
The problem it solves
Say you hold Bitcoin and want Monero, and a stranger wants the reverse. Whoever sends first has to trust the other to send back. The usual fix is a middleman: an exchange or an instant swap service takes both sides’ coins and pays each out. That works until the middleman is hacked, closes, or decides your deposit looks risky and holds it.
An atomic swap removes the middleman. The rules of the two blockchains themselves guarantee that nobody can walk away with both sides.
How it works
The details differ by coin pair, but every atomic swap follows the same outline.
- Agree on a price. The two parties find each other through a peer-to-peer network or an order book and agree on amounts.
- Lock the first coin. One side locks coins in a special transaction that can be claimed in only two ways: by the counterparty revealing a secret, or by the original owner after a time limit.
- Lock the second coin. The other side locks their coins on the second chain under a matching condition tied to the same secret.
- Claim. When one party claims their coins, the act of claiming reveals the secret on-chain, which lets the other party claim theirs.
- Or refund. If anyone stops partway, the time limits expire and each side takes back their own coins.
On Bitcoin-like chains the lock is a hashed timelock contract. Monero has no scripts, so Bitcoin and Monero swaps use a different cryptographic construction built on adaptor signatures. The result is the same for the user.
What you gain
- No custody risk. No company holds your coins at any point, so there is nothing to hack, freeze or seize.
- No account and no ID. You are running software, not using a service. Nobody is in a position to ask who you are.
- No deposit screening. There is no upstream exchange scoring your coins.
What it costs you
- Time. A swap takes as long as both chains need to confirm, plus safety margins. Expect tens of minutes to an hour or more, against a few minutes for an instant swap.
- You must stay online. If your software goes offline at the wrong moment you can miss the claim or refund window. Good clients guard against this, but it is a real difference from “send and wait”.
- Thinner liquidity. You depend on someone wanting the other side of your trade at that moment. Prices are often a few percent worse than a liquid market, and large amounts may have no taker.
- Fewer pairs. Bitcoin and Monero is the best-supported pair. Many coin combinations have no working atomic swap software.
- On-chain fees on both sides. You pay network fees to lock and to claim.
Atomic swap, instant swap or cross-chain protocol
| Who holds the coins | Speed | Can be frozen | |
|---|---|---|---|
| Atomic swap | Nobody | Slow | No |
| Cross-chain protocol | A network of validators, by threshold signature | Fast | Not by one operator; the website you use can block addresses |
| Instant swap service | The company, and often its liquidity partner | Fast | Yes |
Cross-chain protocols sit between the other two. The protocol is decentralised, but the deposit does sit in vaults controlled jointly by its validators while the swap settles, which is not the same as an atomic swap.
Where to do one
Software that runs atomic swaps is listed with the peer-to-peer and swap services, graded the same way as everything else:
- Peer-to-peer exchanges, which include atomic swap clients and escrow-based trading.
- No-KYC Monero exchanges, which shows the no-middleman options beside the instant ones.
- Open-source services and non-custodial services across every category.
A sensible way to start
Do a small swap first, on a stable connection, and leave the software running until it reports the swap complete. Read what the client says about refund timing before you begin. Once you have seen one through, the mechanics stop feeling exotic: it is two locked payments and one shared secret.
