How much information should I share with recruiter

First time dealing with the dynamics of the job market here. I've been contacted by some 3rd party recruiters. I know the "rule" of not sharing your tc or expected tc with the other party in a negotiation, but should I apply it to recruiters too? Or should I see them as allies and be transparent? This is one of the first things I've been asked. One of them also asked me about many details of my current project, I think it was too much. Should I be open (as long as I keep confidential information confidential)? What if the recruiter is from a specific company, is s/he still an ally?