> For the complete documentation index, see [llms.txt](https://docs.lossless.io/protocol/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lossless.io/protocol/technical-reference/lossless-controller.md).

# Lossless Controller

**Lossless Controller** is the core contract of the Lossless protocol. Every lossless protected token calls this contract before every ***transfer***, ***transferFrom***, ***approve***, or any other function. The controller determines if the function can proceed and in cases where it cannot proceed this call reverts in turn reverting the ERC20 function call. 

The controller is an upgradable smart contract that's using an **upgradable transparent proxy pattern**. 

The controller does only a minimal amount of validation and the rest of the logic of lossless protocol lives on other smart contracts (see [Vault and Treasury Protection](/protocol/technical-reference/vault-and-treasury-protection.md)). In the [deployments section](/protocol/technical-reference/lossless-controller/deployments.md), you will find lossless controller addresses for different blockchains.