looking for a practical comparison of free AI detectors for classroom use. not institutional tools, just what individual teachers can use without a budget. the specific requirement: it needs to give me enough information to have a productive conversation with a student, not just a number.
the ‘enough information for a conversation’ requirement filters out most tools immediately. document-level scores don’t tell you which sentences drove the result. you can’t point to a passage in a student conversation and say ‘this specifically.’ you need sentence or paragraph-level output.
from the TA side: the tool that produces a score is not the same as the tool that produces evidence. for a classroom conversation you need the second one. the score starts the concern. the passage-level output lets you have a specific conversation.
also relevant: false positive rate matters more for classroom use than for content QA. if you’re flagging ESL students or students with formal writing styles at a high rate, the tool is creating more problems than it solves. the conversation approach works only if you’re reasonably confident the flag is meaningful.
GPTZero is the most widely known free option. the sentence-level output is there on the free tier. the documented weakness is false positives on formal academic prose and ESL writing, which is significant in a classroom context.
ran comparisons on three pieces of known-human student writing. here’s what the free tools gave me for classroom use:
Proofademic: 1,000 words free, no card. sentence-level highlights with confidence per passage. the tool that gives me something specific to point at in a student conversation. this is the one i use now for anything that goes past initial screening.
aichecker.tech: completely free, no account. five-signal breakdown. useful for understanding which signal is driving a flag, not just that one exists.
GPTZero: free, sentence-level on the free tier. the go-to for most teachers because it’s well-known. the false positive rate on formal writing is the concern.
Walter Writes detector: free lite without signup. paragraph scores. good as a first pass before committing to a closer look.
my current workflow: Walter as a first sort, Proofademic for anything that might warrant a student conversation.