> For the complete documentation index, see [llms.txt](https://startower.gitbook.io/star-tower-chain/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://startower.gitbook.io/star-tower-chain/btc-wallet/what-is-op_return.md).

# What is OP\_RETURN?

OP\_RETURN is equivalent to a "remark function" that can permanently write data into the Bitcoin network. Currently, OP\_RETURN supports up to 80 bytes of data, with punctuation marks, numbers, and letters occupying 1 byte, and Chinese characters occupying 3 bytes.