Here are some resources with good fairly reliable info:

• https://www.erowid.org/ The largest collection of articles, experience reports, safety advice and academic discussion.
• https://psychonautwiki.org/wiki/Main_Page Good quick reference of most safety and dose questions you might have.
• https://pubchem.ncbi.nlm.nih.gov/ good free database of all the chemicals we know about.
• https://getyourdrugstested.com/ FTIR Spectroscopy testing by mail in Canada. Send them a donation if you use them so they can keep helping street people not die from fentanyl for free.
• https://dancesafe.org/drug-checking/ Get your own reagent testing kits.
• https://wiki.tripsit.me/wiki/Drug_combinations quick safety guide to combos.
• https://combo.tripsit.me/ check specific combinations with more info
• https://wiki.tripsit.me/wiki/Main_Page Decent collection of info on safer use and dealing with bad trips, overstimming etc.