A good quality chain tool is an essential part of any home mechanic's toolkit as there is no other way to split a chain. It is important to check if a chain can be rejoined using a chain tool, as some chains feature pins with a mushroom head that are only intended to be rejoined with a quick link. Quite often a bike chain tool can be found on a multi-tool as they can be the difference between the end of a ride and an early bath, or saving the day to ride on. A cheap, poor quality chain tool can bend easily, resulting in the tool breaking, or possibly even damage to the chain itself, so we'd always recommend a quality brand like a Park Tool chain tool. Other tools to consider alongside this are cassette tools and chain whips.