Turnitin Free: _verified_ Class Id

Grammarly uses a massive database of academic papers and 16 billion web pages. It is not as strict as Turnitin with "textual similarity" (it won't flag common phrases), but it is excellent for catching direct copy-paste from websites. Many universities provide Grammarly Premium for free to students.

These are free, but they have strict limits (800-1000 words at a time). They also store your text on their servers. Never paste an entire unpublished thesis into a completely free online tool. Use them for isolated paragraphs only. turnitin free class id