The game is F2P (free to play), but it's P2W (pay to win).
Basically what that means is, if you don't pay to upgrade your power in the itemshop, you will ALWAYS be a gimped, weak, second-rate gamer that won't ever see current endgame content. F2P gamers can't participate in ToSH right now, and most can't do Sardo, or even hardmode Grafu. These are Frogster's "fun zones" that, while accessible to every player, cannot be survived in unless you've spent a LOT for your character in game.
Some people will say, "you can do endgame content as F2P," and I call bullshyt, as I've been playing for years, and even with spending a fair amount on this game on a regular basis, I'm still no where near powerful enough to even clear trash mobs on easy mode ToSH. I'm fully 67/70 geared with full crim/glory/hero/bunk, at least +6 everything, and I'm only sitting on 60k hp. You need 100k min for ToSH. I "could" reach endgame if I spent a grip into the game plussing all my gear to +12 and higher, and possibly tiering my armor higher... but the fact that you MUST purchase items from the shop (including gems which can be a TOTAL scam), ​makes me question just how much actually "is" enough.
You can only garner so much gold in a day to trade for diamond/ruby shop items too... and you'll be shocked how fast that supply will disappear... 50~100m can be spent in just a few purchases. Especially with the "sales" being overpriced ripoffs costing the average player 3~5 times what they should be paying for the items.
Trust me, this game is NOT friendly to F2P gamers, though it does parade around that you "can" still do it. Just be expecting a lot of time consumption, unnecessarily inconvenient methods of doing things, and a severe degree of outcast & isolation from running anything over level 50. But yes, it is "entirely" free to play.