What Is CoinJoin? How Bitcoin Users Mix Coins Without a Middleman

Bitcoin is often called anonymous, but anyone can follow a coin's path from address to address. Much of that tracing starts with one simple assumption: when several coins are spent together in a transaction, they probably belong to the same person.

CoinJoin is a way of breaking that assumption. Instead of each person sending their own transaction, a group of users builds one transaction together, and nobody hands their coins to anyone else.

Here is how CoinJoin works, the main ways it has been built into Bitcoin wallets, what it can and cannot hide, and the legal and practical issues worth knowing before you try it.

What is CoinJoin?

CoinJoin is a method of combining payments from several Bitcoin users into a single transaction. Each participant brings their own inputs and receives outputs at addresses they control.

The idea was proposed by Bitcoin developer Gregory Maxwell in a 2013 post on the Bitcointalk forum. It needed no change to Bitcoin itself. A CoinJoin is an ordinary, valid Bitcoin transaction that simply has several owners.

What sets it apart from a custodial crypto tumbler is trust. Your coins never leave your control. You sign only your own inputs, and only after checking that the transaction pays you what it should.

If anything looks wrong, you refuse to sign, and the transaction never happens.

The problem CoinJoin tries to solve

Bitcoin uses a UTXO model. Your balance is really a collection of separate coins, each one the leftover output of an earlier transaction. When you pay for something, your wallet picks one or more of those coins as inputs.

Chain analysts treat inputs spent together as belonging to one wallet. This is known as the common-input-ownership heuristic. Satoshi Nakamoto flagged the issue in the Bitcoin whitepaper, noting that multi-input transactions "necessarily reveal that their inputs were owned by the same owner."

Add change outputs, address reuse and deposits to exchanges that know your name, and a lot of someone's financial history can be pieced together from public data. Anyone can try a basic version of this with a block explorer.

CoinJoin weakens that first assumption. If a transaction has inputs from ten different people, spending them together no longer says anything about who owns what.

How a CoinJoin transaction works

The details vary between wallets, but a typical round looks like this.

Registration. Participants announce which coins they want to mix and which fresh addresses should receive the outputs. A coordinator, or in some designs another participant, collects this information.

Equal outputs. The transaction is built so that many outputs share the same value, for example 0.05 BTC each. If five people each receive 0.05 BTC, an outside observer cannot tell which output belongs to which input.

Signing. Each participant checks the finished transaction and signs only their own inputs. Once every signature is in, the transaction is broadcast and confirmed like any other.

Change. Anyone who brought more than the standard amount gets the rest back as a separate change output. That change is not mixed, and it can still be linked to the original coins.

The group of indistinguishable outputs is called the anonymity set. Five equal outputs give an anonymity set of five, while a round with a hundred participants offers far more cover.

Many users repeat the process, known as remixing, to grow that set further.

The main CoinJoin wallets and tools

Several projects have turned the idea into usable software. Each gives a different answer to the same question: who organizes the round?

JoinMarket

Chris Belcher announced JoinMarket in January 2015. It works as a market. "Makers" keep their coins available for mixing and earn a small fee, while "takers" pay that fee to run a CoinJoin straight away, for the amount they choose.

There is no central coordinator. The weak spot in this model was the risk of one person running many fake makers, known as a Sybil attack, and quietly seeing through other users' mixes.

Version 0.9.0, released in 2021, added fidelity bonds. Makers lock bitcoin in time-locked addresses, and takers favor makers with more valuable bonds, which makes faking many identities expensive.

Wasabi Wallet

Wasabi Wallet is a desktop wallet that released version 1.0 in October 2018. Version 2.0 followed in June 2022 with a protocol called WabiSabi, which uses anonymous credentials so the coordinator can run a round without being able to link inputs to outputs.

WabiSabi also allows outputs of varied amounts, so users with smaller balances can take part without being forced into one fixed size.

zkSNACKs, the company behind Wasabi, shut down its own coordinator on June 1, 2024. The open-source wallet still works, and users can point it at third-party coordinators instead.

Whirlpool

Whirlpool, built by Samourai Wallet, took a stricter approach. Every mix had five inputs and five equal outputs, in fixed pools of 0.001, 0.01, 0.05 and 0.5 BTC. A preparatory transaction called Tx0 split deposits into pool-sized pieces and paid a flat pool fee.

Samourai's founders were arrested in April 2024 and the service's servers were seized. In November 2025 they were sentenced to five and four years in prison after pleading guilty to running an unlicensed money transmitting business.

What CoinJoin does not hide

CoinJoin improves privacy, but it has clear limits.

CoinJoins are easy to spot. Transactions with many equal outputs stand out on chain, and analytics firms label them. Academic researchers have shown that Wasabi and Samourai transactions can be detected with fairly simple methods.

Change can undo it. The unmixed change output stays tied to your original coins. Spend it together with mixed coins later, and you reconnect the two.

Small anonymity sets offer little cover. A round with few real participants, or with participants secretly run by one party, hides much less than the output count suggests.

Your own habits matter most. Sending mixed coins straight to an exchange account in your name, or merging several mixed outputs in one payment, can hand analysts the very link the CoinJoin was meant to break.

Is CoinJoin legal?

In most countries, using a CoinJoin wallet is not a crime in itself. Legal pressure has focused on the people who run coordination services, especially in the United States, where prosecutors have argued that such services can count as money transmitting businesses.

For ordinary users, the more practical problem is often their exchange. Many exchanges screen deposits with blockchain analytics, and coins with recent CoinJoin history can be flagged, delayed or rejected.

Some users have been asked to explain where their funds came from. Rules differ by country and by platform, so check both before mixing coins you plan to sell later.

PayJoin and other ways to protect your privacy

CoinJoin is not the only option. PayJoin, described in Bitcoin Improvement Proposal 78, lets the sender and the receiver of a payment both add inputs to the same transaction.

The result looks like an ordinary payment, yet it breaks the common-input assumption without the telltale equal outputs. Several wallets and the BTCPay Server payment processor support it.

Everyday habits help too. Use a fresh receiving address for each payment, avoid merging coins from different sources, and use coin control to pick exactly which coins you spend.

Running your own Bitcoin node also stops your wallet from revealing your addresses to outside servers.

The bottom line

CoinJoin lets Bitcoin users pool their transactions without trusting anyone with their coins, which has made it one of the best-known privacy techniques on Bitcoin. JoinMarket, Wasabi and Whirlpool each struck a different balance between ease of use, cost and who coordinates the rounds.

It works best as one part of a wider set of habits. Large anonymity sets, careful handling of change and a clear view of how your exchange treats mixed coins matter as much as the transaction itself.