The U.S. Judo Federation has a document which goes over rank requirements in fine detail:
That's just one example from one Judo association that I got from a quick Google just now. There are many other examples.
Each particular school you go to has its own requirements for each belt. They may belong to a national or international judo organization. But there's still room for them to change the syllabus around. It just depends on the instructor.
There are typically these requirements for each rank:
- Minimum age.
- Minimum time spent at the current rank.
- Being able to demonstrate clean throwing, holding (including pins, joint locks, and chokes), and breakfalling techniques.
- Kata (albeit typically an after-thought in Judo).
- Japanese terminology.
- Jumping over Bruce Lee's nunchucks. Just kidding. :)
And in some associations, you may be required to win in tournaments. There may be less time needed in your current rank if you are actively engaged in competition.
Most of your time in Judo will be spent learning throws and being thrown. Following that will be holds and groundwork. Following that will be randori. In later ranks, randori and scenario-based randori / drills will probably become the dominant percentage of time you spend in class.
Each rank has a list of new techniques to learn and perform cleanly. At first they will be in isolation, but later on you'll be asked to integrate them in combinations. For example, you might have to demonstrate Osoto Gari followed by Kesa Gatame. And you might already know a technique from a previous rank, but you'll be asked to show more advanced variations of it.
There's not a lot of material in Judo compared with many other martial arts. There's the Go Kyo No Waza, which is the 5 levels / groups of throws you have to know. That totals just 65 throws, more or less, depending on your school's curriculum. Most of the throws you perform in competition will be a handful of maybe 8 throws that you learn in the first couple years. There aren't a lot of holds, either. Most of the learning you'll do, therefore, will be how you deal with a resisting opponent and still be able to perform these techniques. That comes over time with experience.
Boxing is the same way. In boxing, there really aren't that many actual techniques. You got the jab, the upper cut, the cross, the hook, maybe the corkscrew punch, and not a whole lot else. But in order to make those techniques work on a resisting opponent, you're going to have to learn all about timing, distancing, strategy, decoying, level changing, bobbing and weaving, covering, advanced step work, and so on. Add to that the athleticism and conditioning you need in order to keep going multiple rounds. It's deceptively complex.
Getting back to Judo... I think you need to go to your particular Judo school of interest and ask for their belt requirements if you really want to be exact. When I trained in Judo back in high school, I was given an information packet that outlined all of the requirements for each rank up to 1st dan. That was thanks to a good teacher who cared enough to write it up. I would imagine many other schools do that as well.
Suffice it to say, though, it's not going to seem like an overwhelming amount of material to learn at each rank. Rather, Judo is all about repetition. You will learn just one or two throws to begin with, and you're going to repeat those throws with a partner thousands of times before learning the next throw. So I wouldn't worry about the amount of material to learn. You can definitely handle it.
As for rushing through the ranks, you're limited by the minimum amount of time you need at each rank. So my advice is not to worry about rushing through the ranks. Just show up to all your classes and really make everything you do count. Really work at it. Your hard work is what will pay off later on.
Hope that helps.