OnRubric vs Grammarly AI Grader

Both tools predict how your paper will score. Grammarly's AI Grader lives inside Grammarly's own editor and comes with the rest of the Grammarly subscription. OnRubric only predicts the rubric score: one range per criterion, with the sentences behind it, built around the rubric your course posted. Here is what each does, taken from Grammarly's own pages on 2026-10-14, and what we could not verify.

What Grammarly AI Grader does

Grammarly launched AI Grader on August 18, 2025 as one of its "AI agents". It runs inside Grammarly docs (the editor at app.grammarly.com), in a panel beside your text. You can add a rubric or assignment guidelines, or let it "check with basic guidelines"; Grammarly says the feedback is "aligned to uploaded rubrics, course information, and writing topics". It returns a predicted grade plus suggestions "at both the document and paragraph level", and the prediction updates as you edit.

On the free plan you can "predict your grade and get three pieces of personalized feedback on your writing for free once per day". Pro gives "unlimited grade estimates and detailed feedback on your entire paper". Pro costs $30 a month billed monthly, $60 a quarter, or $144 a year; students get 50 % off Pro through SheerID verification for one subscription period. Papers must be in English.

Grammarly is clear about limits: the estimate "should not be taken as your actual grade" and is "not a 'replica' of your professor". There is "no instructor-facing component". It warns that "AI generates the rewrite suggestions, so if you use them, your work could be flagged for AI use". It does not check for plagiarism.

What OnRubric does

You paste the paper and the rubric (or photograph the rubric, or pick one from the library). OnRubric scores every criterion of the rubric separately, as a range, and for each criterion shows one to three sentences copied verbatim from your text that earned or lost the points; a quote that cannot be found word-for-word in your text is flagged. Then it ranks the three fixes with the largest expected gain, each with a one-sentence example and never a rewritten paragraph, runs a deterministic APA 7 check (in-text citations against the reference list, DOIs against CrossRef), and, after you edit, shows the delta per criterion.

Checks are free during the beta and need no account. The paper is kept 30 days so the report link can reopen it, then deleted, and you can delete it sooner yourself; it is not used to train models. The score itself is a rough estimate: on 68 essays that people had already scored, it missed by 11 % of the maximum on average.

Side by side

	Grammarly AI Grader	OnRubric
Where it runs	Inside Grammarly docs (app.grammarly.com)	Any browser; paste, upload, or photograph
Rubric input	Paste rubric or assignment guidelines; optional course info	Paste, photo of the Canvas or Blackboard table, or a library rubric by assignment type
Output	Predicted grade, document- and paragraph-level suggestions	Predicted range per rubric criterion, verbatim evidence per criterion, three ranked fixes, APA 7 check
Evidence for the score	Passage-level feedback beside the text; whether it quotes your text per criterion is not stated	Every criterion quotes sentences from your text; quotes not found in your text are flagged
Rewriting	Offers rewrite suggestions (Grammarly warns they may be flagged as AI use)	No rewrites; a fix may include one AI-written example sentence, which carries the same risk if pasted in
Re-check after edits	Yes, the prediction updates live	Yes, with a per-criterion delta against the previous draft
Free tier	One grade prediction and three feedback items per day	Free during the beta; limits after the beta not set
Price	Pro $30/month, $60/quarter, $144/year; students 50 % off	Beta: free; paid plans not set
Accuracy published	None found on Grammarly's pages (2026-10-14)	Average miss of 11 % of the maximum score on 68 essays scored by people; shown as a wide range for that reason
Plagiarism check	No	No

What we could not verify about Grammarly

Grammarly's pages do not say whether the grade comes as a letter, a percentage, or points; whether the rubric is scored criterion by criterion; whether the feedback quotes your text as evidence; or what file types and document lengths are accepted. Launch coverage in August 2025 described an "Expert Review" agent and an option to enter your instructor's name and school; neither appears on Grammarly's current pages, so we treat them as unconfirmed.

Which to use

If you already pay for Grammarly and write inside its editor, AI Grader is one panel away and worth running. If your grade depends on a specific rubric with named criteria, and you want to see exactly which sentence cost which point before you change anything, that is what OnRubric is built for. Using both is fine; neither is your instructor.

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OnRubric is not affiliated with, endorsed by, or sponsored by Grammarly. Grammarly and AI Grader are trademarks of their owner and are used here only to identify the product being compared.

Sources (read 2026-10-14): AI Grader · AI Grader user guide · Launch announcement · Pro pricing · Plans · Student discount · Authorship