> For the complete documentation index, see [llms.txt](https://erroldrummond.gitbook.io/halo2-tutorial/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://erroldrummond.gitbook.io/halo2-tutorial/section-3/gadgets.md).

# Gadgets

In this section we want to walk you through some gadgets. Gadgets are sub-circuits that were built by others that you can make use of. For example, if somebody else spent months implementing the hash function keccak and ensuring it was both safe and optimised, why would you then build it all yourself again from scratch? You wouldn't of course, you would make use of their gadget for it (provided you trusted its quality).

Other gadgets include a range gadget or ECDSA signature verification in arbitrary fields.