Been messaging this girl on tinder today and we've been getting along fairly well. I only want to hookup with her but I don't want to go on a date or spend more effort. What do I do?
If you don't want her to have false ideas, be clear up front.
"Look, I'm really not looking for a relationship right now. I just want to keep it casual."
That is as clear as you can get without explicitly saying "I just want to fuck you." If she's into that, great! Everyone gets what they want. If she isn't, then you may not get to fuck her, but the advantages are: 1) you won't have to deal with an awkward situation (that you yourself have made) later on, and 2) you won't have been a complete asshole.
Here's what you do op:
>get her to come to your house for Netflix and chill
>she'll know what it means
>if she doesn't come to your house you're not getting laid and then trying to get laid will become a fruitless endeavor.