TOEFL iBT writing scores are based on a 0 ~ 5.0 point scale (as opposed to a 0 ~ 4.0 scale for speaking tasks). You may be wondering how these scores are determined. Well, you've come to the right place to find out!
The specific requirements for the two different tasks (integrated writing task or independent writing task) are explained in the links provided below:
Writing Task 1 (Integrated Writing Task):
http://www.onlinenglish.net/iBT/Writing_rubric_Integrated_English.html
Writing Task 2 (Independent Writing Task):
http://www.onlinenglish.net/iBT/Writing_rubric_Independent_English.html
So if you see that I have allocated you an iBT TOEFL score for your essay and wonder how I came to that conclusion about your writing, now you can see the actual rubrics for yourself!
Best wishes,
~ Jason