A tumbler is described in full under crypto mixer or crypto tumbler, which covers how mixing services work, their legal status and the enforcement actions taken against them. This page explains the single word as it appears in crypto and compliance discussions.
A tumbler takes cryptocurrency from many users, pools it and pays out equivalent amounts to new addresses, often after random delays and in varied amounts, so that observers of a public blockchain struggle to tell which incoming payment matches which outgoing one. Custodial tumblers hold users' coins during the process, while non-custodial designs such as CoinJoin or smart contract pools let users mix without handing over control. Some criminals pass funds through several services in a row, known as daisy-chaining tumblers.
"Tumbler" and "mixer" mean the same thing; the first evokes a tumble dryer churning coins together, a play on the laundering metaphor. Privacy advocates defend mixing as a way to protect legitimate financial privacy on transparent ledgers. Regulators and law enforcement agencies associate tumblers with money laundering by hackers, ransomware groups and sanctioned states, and several operators have been prosecuted. In 2022 the US Treasury placed the Tornado Cash smart contracts on its sanctions list, a decision it reversed in 2025 after court challenges. Exchanges commonly flag or freeze deposits traced to tumblers.