> For the complete documentation index, see [llms.txt](https://dev.bondprotocol.finance/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dev.bondprotocol.finance/smart-contracts/bond-system/callback/callback-interface.md).

# Callback Interface

The Callback Interface defines the functions that all Callback contracts should implement. These have been kept to a minimum to the functions necessary to ensure functionality and security. Each Callback contract should implement:

```solidity
callback
amountsForMarket
whitelist
deposit
withdraw
```