Every free SOP checker is a funnel to the paid plan. That is fine. The real question is whether the paid plan funnels you toward anything useful, or just a receipt.
Free tiers reliably cover the basics: spelling, core grammar, punctuation. For most applicants, that is eighty percent of the value right there. Your draft's biggest mechanical risks are the errors you are blind to, and free checkers catch those. Run every draft through a statement of purpose checker app free tier before any human sees it. Non-negotiable.
Paid tiers add style suggestions, tone analysis, deeper structural feedback. Useful, sure. But ask the uncomfortable question: are you buying twelve months of a subscription to polish one essay? Most people touch the paid features for two weeks. If you upgrade, pick monthly billing, never annual. Better yet, time the free trial for your final revision week and cancel like you mean it.
Know the hard limit, free or paid. An SOP grammar and structure checker tool grades sentences, not stories. It cannot tell you your motivation sounds generic. It cannot tell you paragraph three repeats paragraph two. Anyone who claims an app replaced their human reviewer is either lucky or lying.
My stack: free checker on every draft, one month of paid during final revisions if the price is sane, then a human for the last pass. A statement of purpose review app covers the middle ground, and any SOP editor app on iOS or Android should be judged on export and offline before anything else.
One last thing no checker does: tailor the essay to a specific university. The tailoring packs at sopexpert.fyi handle that part.