To replace a driveside spoke (the most likely breakage) you need to take off the cassette, requiring a chain-whip, lockring remover and adjustable spanner – or this 12g steel tool.
As with the more paintwork-friendly (but also more expensive) NBT2, you ﬁt this to the lockring and put the wheel back in the frame, with the tool braced at the dropout. By turning the cranks, the chain rotates the cassette and loosens the lockring. Make sure the quick release is tight.
To tighten up a reﬁtted lockring, brace the tool against the chainstay and rotate the wheel by hand. It’s intended for use on sturdy tourers; use it on a carbon ﬁbre or lightweight aluminium machine and you may damage your bike.
The Unior tool ﬁts Shimano-style lockrings and includes a decent spoke key for 3.3mm/European nipples. It doesn’t come with any instructions for use, unfortunately.