I like bullshitting around about hatching seedlings and grow various plants indoors and in my garden. But the one with the real green thumb in this house is my wife. So I, for my part, have to rely on technical utilities in order not to either drown or dry out my windowsill greens.
This is what I use (available on amazon). It can tell you the soil’s moisture (cool and important), the ph-value (who cares?) and the amount of sunlight (couldn’t care less) for your plants.
Note: I don’t have any affiliate-link or something the like to Amazon (I suppose they would laugh out loud if I came up to them with that). I post this here simply because it’s useful to me and that’s where I got it from.