Noplag

How Noplag detects plagiarism, what it honestly can't do yet, and why the code that decides is public. Written by the people who build it.

The algorithm that finds copied text across more than 150 million documents fits in about thirty lines of Python. Here's how winnowing works and why we chose it.

Three commands get you a working plagiarism checker that never sends a document anywhere. Here's who should self-host, what it takes, and the trade-offs nobody puts on the pricing page.

Our engine detects verbatim and near-verbatim copying. It does not detect paraphrase. Every plagiarism checker has this boundary — we're just the ones who put it in writing.

Start free with the open-source engine. Upgrade when you need the cloud corpus, multilingual coverage, or team features.

Noplag vs Turnitin, iThenticate, Copyleaks, Grammarly, Originality.AI, Quetext, GPTZero — written so you can pick the right tool, not so we win every row. Some categories Noplag doesn't lead in. We say which.

Two API-first detectors targeting developers and SMBs. We'll be specific about where Copyleaks is genuinely better — and where the open-source approach pulls ahead.

GPTZero is the AI-detection brand most educators recognise. Noplag is a full plagiarism + AI specialist with documented ESL calibration and an open-source algorithm. Both have the same Stanford-paper bias problem; we mitigate it, GPTZero acknowledges it.

These are not really the same kind of product. Grammarly is a writing assistant where plagiarism is one feature in the Premium bundle. Noplag is a dedicated plagiarism + AI-detection specialist. Most writers want both.

Twelve years of plagiarism detection. From a Kyiv apartment to a San Francisco headquarters, through a New York accelerator, a million checks, and one deliberate rebuild. This is how Noplag got here — and where it goes next.

Noplag is built by a small team, and the same people who write the code read the inbox. Pick the address that matches what you need and we'll take it from there.

Open-source engine, multilingual corpus, live-web verification. Trusted by 12,000 writers, researchers, and educators since 2014.

How Noplag handles the documents you check, the fingerprints we store, and the rights you have over your data. Written to be read, not to hide behind. The short version: we never train models on your documents, and you can delete everything we hold in one click.

The agreement between you and Noplag when you use the product. Plain-language summaries open each section; the detail follows. Creating an account or running a check means you accept these terms.

Open-source engine, multilingual corpus, live-web verification. Trusted by 12,000 writers, researchers, and educators since 2014.