How to find 5e DM materials online, preferably for free? [duplicate]

The reason I’m asking this is because of, quite simply, the Monster Manual. As a DM, I know I’m probably gonna need it, but not all the time. So instead of buying it physically, I want to see if there is a free online way to access it. If you could also find a way to get Xanathar’s Guide to Everything the same way, that would be great as well. I’m not talking about campaign books by the way. Someone suggested How do I find quest books for sale? as a alternative question with answers, but again, I’m not talking about campaign books (yet)