Mark faster. Learn why every sentence scored the way it did.
Teachers grade a full class in minutes. Students see exactly which sentences earned marks, which lost them — and what to fix. Colour-coded, sentence by sentence, against your actual rubric.
Free to start · no credit card · works for any essay subject
Renewable energy is the most effective way to cut carbon emissions. Solar capacity has grown tenfold in the past decade, according to the IEA. This shows that clean power is becoming cheaper and more common. Also cars are bad and we should fix them too. Investing now protects both the economy and the environment.
This sentence is off-topic. Tie it back to carbon emissions or remove it — it hurts your argument score.
↑ Fix this → +2 marks
What actually changes when you use CoMarker
Built for teachers who are time-poor. Built for students who deserve better feedback.
For teachers
Before
30 essays sitting on your desk for two weeks, each one needing individual comments
After
30 essays marked, commented, and ready to return in under 10 minutes. You stay in control — skim the highlights, tweak any grade or comment, and release polished feedback your students can actually act on.
For students
Before
A number at the top of the page and one vague line you forget before you even get home
After
Students submit their own work and get every sentence highlighted — colour-coded, explained, and tied to the rubric. They see exactly what worked, what didn't, and why. No more guessing.
For real improvement
Before
Students repeating the same mistakes every assessment because feedback never stuck
After
Targeted next steps tied directly to the rubric mean every piece of feedback is a lesson. Students build on what they learn — essay after essay, assessment after assessment.
How it works
Three steps from a stack of essays to feedback that lands — with a teacher in the loop the whole way.
Upload the task and the work
Drop in your rubric and the actual task or stimulus sheet, then add the class set of essays — PDFs, docs, or scans.
CoMarker marks against your criteria
Every essay is graded sentence-by-sentence against your rubric and the task you set, with colour-coded highlights explaining each mark.
You review, adjust, and release
You stay in control. Skim the highlights, tweak any grade or comment, and release polished feedback students can actually act on.
Built to mark the writing, not skim it.
Most AI graders spit out a number and a paragraph of generic advice. CoMarker reads the way you do — sentence by sentence — and ties every highlight back to a specific rubric criterion.
- Sentence-level colour coding shows students precisely where they hit or missed the mark.
- Graded against your task sheet, so feedback reflects what you actually asked for.
- Every comment maps to a criterion, making moderation and feedback conversations easy.
Hover any highlighted sentence in the example to see the criterion and feedback.
Climate change is one of the most urgent challenges facing our generation, and its effects are already visible worldwide. According to NASA, global temperatures have risen by roughly 1.1°C since the late 19th century. This warming has caused ice caps to melt and sea levels to rise, which is bad for lots of places. Many scientists think we should do something about it soon. In conclusion the world is getting hotter and thats a big problem for everyone. Governments should invest in renewable energy because it reduces emissions. Also plastic is a problem and pollution too. By acting now, we can protect ecosystems and build a more sustainable future for the next generation.
Everything you need to mark faster and fairer
Students can check their own work — independently
Submit your own essay and instantly see every sentence highlighted — colour-coded, explained, and tied to the rubric.
Find out exactly what earned marks, what didn't, and what to fix — before the final submission.
No waiting. No guessing.
Sentence-level highlights
Colour-coded spans show exactly which sentences earned or lost marks.
Grades against your task
Marks are tied to the actual task or stimulus sheet you set — not a generic prompt.
Your rubric, your criteria
Upload any rubric and CoMarker maps every comment back to your criteria.
A full class in minutes
Batch a whole set of essays and get consistent marks back fast.
Actionable feedback
Specific, criterion-linked comments students can actually use to improve.
Teacher-in-the-loop
Review and override every grade and comment before anything is released.
Built for K-12
Designed around how teachers actually mark, from primary through senior years.
Privacy-first
Student work is handled with strict access controls and clear retention.
From marking marathon to a quick review
| Without CoMarker | With CoMarker | |
|---|---|---|
| Turnaround for a full class | A weekend of marking | Minutes, then a quick review |
| Feedback students get | A grade and a vague comment | Sentence-level, colour-coded highlights |
| What the marking is based on | A generic AI prompt | Your rubric and your actual task sheet |
| Consistency across the class | Drifts as you tire | Same criteria applied to every student |
See CoMarker in action
From rubric to colour-coded feedback in seconds.
Rubric — Year 10 Imaginative Writing
Out of 20Thoughtful, imaginative piece with consistent focus. Effectively crafts narrative elements and fantasy conventions with strong language choices.
Effective imaginative piece that explores a relevant theme. Developed narrative elements and intentional language choices.
Imaginative piece with some use of stimulus. Some narrative elements present; variable control of language.
Inconsistent or limited response to stimulus. Limited engagement with narrative elements and language.
Attempts to compose a piece in response to a stimulus. Minimal control of language.
Student data stays protected
Encrypted in transit and at rest
Essays and rubrics are protected with industry-standard encryption.
Never used to train public models
Student work is not sold or used to train third-party foundation models.
Clear retention and deletion
You control how long work is stored and can delete it on request.
Rolling out across a whole school?
CoMarker helps departments mark faster while keeping standards consistent — with the controls admins need.
- Consistent marking across every teacher and class
- Shared rubrics and moderation to keep standards aligned
- Admin controls, teacher seats, and simple onboarding
- Procurement-friendly invoicing and a real human to talk to
Frequently asked questions
Mark your next class in minutes.
Start free — no credit card. See sentence-level feedback on your own essays today.