Free limits, per request and per month. Two different numbers, and vendors lead with whichever flatters them. The per-request cap decides whether a real document goes through in one pass; the monthly figure decides how long you last. A tool can win one and lose the other badly.
Price per word, not price. Divide the entry plan's cost by its word allowance before comparing anything. A cheaper plan with a tenth of the capacity is not cheaper. Do it at the tier you would genuinely buy.
Transparency. Does the vendor publish a month-to-month price, or only an annual-equivalent figure? Does it state its free per-request cap, or leave it vague? Are there two plans priced within a dollar of each other where the cheaper one is capped? Each of those is a published fact, and each tells you how the vendor will treat you later.
Privacy and retention. Three questions: is your text stored, for how long, and does it train a model. This is the check people skip and the one that matters most if you paste work you do not own. Our policy and what we do with your text are both published; check each vendor's for yourself rather than taking a comparison page's word for it, this one included.