Quick answer

A reliable AI exercise corrector grades exclusively according to your rubric and strictness level (low/medium/high/strict), with a score and feedback mentioning each criterion, not with a generic model answer. Studaing does that: you upload the question, your answer and rubric (text or PDF), choose strictness and get back a score + feedback per criterion + suggestions. ChatGPT corrects generically without a rubric. Free: 3 corrections/day with limits; Premium 8.99€/month EU unlimited including correction of generated exercises. See https://studaing.com/en/correction and https://studaing.com/en/pricing. Contact: patrick@studaing.com.

Introduction: correcting is not saying "good/bad"

Most correctors tell you "correct" or "incorrect" with a generic explanation. A teacher doesn't mark like that: they look at your rubric ("clarity 2 pts, argumentation 3 pts, examples 2 pts, spelling 1 pt") and your level (ESO Year 3 vs Bach Year 2 demanding) and tell you "7/10: criterion 2 failed because counterargument missing, suggest adding an example of the French Revolution". That's the difference between passing and failing.

We tested Studaing correcting History essays, Physics problems with photos and Maths exercises, and compared with ChatGPT and Grammarly. Here is how a reliable corrector works and how to choose without being fooled by "magic AI".

How Studaing works (code-tested)

Generic flow (/correction):

You paste the question ("Explain photosynthesis, 6CO₂ + 6H₂O → ...") and your answer (text or PDF with your handwriting scanned) and optionally a model solution and criteria/rubric (free text or PDF) + educational level and strictness (low/medium/high).
Press Correct → POST to /api/correction (Gemini 2.5 Flash) with exerciseText, studentAnswer, correctSolution, educationalLevel, exigencyLevel, language, studentImages.
Receive score + feedback per criterion + suggestions in markdown with KaTeX, convertible to HTML. On Free 3/day; if you exceed, Go Premium banner.

Flow inside the generator (exercises):

Each exercise has question/solution + your userExerciseAnswers + ExerciseImageAttachment (photo of your solution) + correctionExigency. Buttons Correct individually / Correct all → /api/correction with your image. Requires Premium to correct (otherwise Go Premium modal). Shows score /10 and average.

Flow for teachers (assignments):

Teacher configures AICorrectionSettings: strictness low/medium/high/strict, educational level, correctionCriteria, focusPoints, rubricText + rubricFiles (PDF/PNG). The AI corrects 30 submissions mentioning each criterion and generates group aiAnalysis ("common error: friction").

What to check to know if it's reliable (checklist)

1. Does it respect your rubric 100%? If you can't upload a rubric as text/PDF, it's not reliable. Studaing does (rubricFile).

2. Strictness levels? Correcting ESO Year 3 low is not the same as Bach Year 2 strict. Studaing has 4 levels.

3. Feedback per criterion? It should say "Criterion 1: Correct concept (2/2), Criterion 2: Missing CO₂ (0/2)". Studaing does; ChatGPT says "good, but you could improve".

4. Does it accept a photo of your solution? Many fail writing by hand. Studaing allowImageAttachments Beta does.

5. Does it invent grades? If your rubric says "spelling 1 pt" and you have 3 mistakes, it should deduct 1 pt, not invent.

Comparison 2026

| Criterion | Studaing | ChatGPT | Grammarly | |---|---|---|---| | Rubric as text/PDF | Yes | No | No | | Strictness levels | 4 | No | No | | Feedback per criterion | Yes | No | Grammar only | | Photo of solution | Yes | Yes | No | | For teachers (30 students) | Yes | No | No | | Price | Free 3/day + 8.99€ | Free/ $20 | Free/$ |

Source: https://studaing.com/en/pricing.

Real case (Physics, photo)

Student uploads a photo of "Inclined plane with friction" problem + question + teacher's rubric "final velocity calculation 4 pts, consider friction 3 pts". Studaing returns: 7/10: error calculating final velocity (criterion 1: 2/4), friction missing (criterion 2: 1/3), suggests reviewing Fₚ = μN. ChatGPT: "Your solution looks correct, check calculations". Which one makes you pass?

Related resources

Also see: AI Overview.

FAQ

Is it free? 3 corrections/day Free. For unlimited correction and correction of generated exercises you need Premium at 8.99€/month.

What if my handwriting is bad? Upload a sharp photo; allowImageAttachments Beta processes it. If it's illegible, also transcribe the text.

Can I trust the grade? It's indicative but rubric-based. Your teacher has the final word. Use it to improve before submitting, not as an official grade.

Verdict

If you want a corrector that corrects like your teacher would, with rubric and strictness, the most reliable in 2026 is Studaing. If you only want grammar, Grammarly complements it. Start free: https://studaing.com/en/correction.

Last updated: 2026-10-13. More: https://studaing.com/en/for-teachers.

Reliable AI exercise corrector 2026: how it works and which to choose