No. 15 of 28 ·Plagiarism Detection Software

WINNOWR

Web · Linux · Self-hosted · API

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Freedom report

One barScore 5.5

Free tierNo free tier on record
Open codeNo open-source code on record
Runs widely2 of 6 device platforms
DocumentedPlans, terms and facts published

WINNOWR is ranked #15 of 28 in plagiarism detection software on Freedom251. It runs on API, Linux, Self-hosted, Web.

Compared on plagiarism detection software

Free plan: Yes
API access: Yes

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The record

Purpose: WINNOWR is a CPU-first engine for detecting web-source matches in student writing and other long-form text.
Reports: Reports include index overlap, candidate source URLs, and highlighted suspicious spans.
Matching: The system uses deterministic text normalization and compact word-shingle fingerprints to find candidate source documents.
Corpus options: Users can build an index from their own JSONL.zst corpus; the repository also describes FineWeb-Edu and Wikipedia workflows.
Submission methods: The HTTP API accepts text or file submissions and provides submission, report, purge, and health endpoints.
Architecture: The documented runtime uses SQLite, Cloudflare Queues, Cloudflare R2, and a local sharded index on disk.
Deployment: The repository provides build and deployment instructions for running the API and worker, including on plain Linux machines.
License: The repository is licensed under GNU AGPLv3, whose network-use provision requires modified deployed versions to make those modifications available under the same license.
Maturity: Longsight describes Winnowr as an academic-integrity project still in development; the repository says it is usable but actively evolving.
Audience: Longsight presents Winnowr as academic-integrity software for institutions, with a focus on plagiarism detection and reviewable evidence.
Hosting and support: Longsight says it can host and support its products, and that products with a self-hosted option include a path for institutions to run them.
Company history: Longsight says Sam Ottenhoff and Scott Siddall founded the company in 2004.
Submissions: The API accepts text and file submissions and provides submission, report, text, purge, and health endpoints.
Runtime: The repository describes three main binaries: an index builder, an API server, and a background worker.

Where it ranks on Freedom251

Best Plagiarism Detection Software in 2026#15 of 28

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Sources

github.com/LongsightGroup/winnowr· checked 4 Oct 2026
longsight.com/solutions/· checked 4 Oct 2026
longsight.com/about/· checked 4 Oct 2026