how much content does online have?

[Based Duffle Bag Boi]

im planning to buy the game for its multiplayer online is it worth?

[SodiumChlorideNaCl]

its an old game. have you never played GTA V before? Online is pretty much grinding missions and robbing ♥♥♥♥♥ so you get to have money and buy ♥♥♥♥ you want. Its fun in some cases, but boring in some other areas as well

[Caped Crusader]

There's been a healthy number of DLCs for GTA Online - adding businesses, heists, races, more businesses, more races, more heists, etc. - and I would suspect that will continue, though perhaps at a slower pace. They're all free, technically, but when it comes to making the best money from them there's usually a steep cost involved, and that's where the grind comes in.

https://www.gtaboom.com/gta-online-update-dlc-history/

[SqueakyTweaky]

Plenty, you will sink a good thousands hours in without noticing it.