These are my desert island tools which I would not be without!
First up, my Japanese steel rule, which I love especially because it has an anti-glare finish, so you don't get those reflections which make it difficult to see the measurements. I also love that it is only calibrated in mm and cm, as I never use inches.
A bone folder is probably the most used tool in a bookbinder's studio, used to generally poke, prod, score, persuade, encourage and lift! Traditionally they are made of bone, although nowadays you can also find them made of teflon or bamboo. It is mainly for folding- you can use it to get a really sharp fold- but it is also really useful for all sorts of other jobs like pushing paper or cloth into nooks and crannies, and for rubbing down paper to make sure it sticks.
The scalpel is an essential cutting tool for very precise work. I like the surgical kind and mostly use 10A blades. I could measure my life in scalpel blades; they need to be changed very frequently.
A cobbler's knife is a lovely thing. It slices through paper like butter, and I love the rhythm of the process of folding and cutting, folding and cutting, to transform full size sheets of paper into a stack of sections ready for sewing.
I use my Japanese screw punch for making perfect holes in leather and handmade paper. It's a joy to use, with only the slightest pressure needed. It is invaluable when I make the Handmade Paper Notebook with Vellum Plackets.
Last but not least, my little leather covered weight is always by my side at the work bench. It's useful for supporting a text block when repairing a book, lightly weighting a stack of folded sections, holding a book in position while its being photographed, and has a thousand other uses. It's clean and soft so can be used directly on paper or leather without marking or damaging the surface.
There are many other well-loved tools in my studio, but these six are always within reach and are used every day.