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Noplag Engine
San Francisco, United States
What it is
Noplag Engine is an open-source tool for finding verbatim and near-verbatim matches against a corpus you control. It uses fingerprints to identify possible sources, then aligns matching character ranges. Reports include similarity by source, matching passage offsets, and coverage accounting. The engine can ingest .txt, .md, .pdf, and .docx files from folders or through HTTP upload. Its /v1 API supports checks, reports, uploads, progress events, and corpus management, and ships without authentication. The open-source engine searches a local corpus; the hosted product also searches the live web. It does not detect paraphrase, semantic similarity, or AI-written text. The engine is licensed under Apache 2.0 and can run on your hardware with Docker Compose. The repository lists Python 3.12 or newer for development and PostgreSQL in its Docker Compose setup. The hosted Free plan provides three checks per month, with up to 2,500 words per check; self-hosting allows unlimited local checks. Pro costs $9.99 a month and includes 50 checks per month, up to 25,000 words per check, a REST API, and webhooks. Premium costs $19.99 a month. Enterprise pricing is custom.
For and against
For
- Open-source and licensed under Apache 2.0.
- Can run on user hardware with Docker Compose.
- Reports include matching passage offsets.
- Supports .txt, .md, .pdf, and .docx ingestion.
Against
- Does not detect paraphrase or semantic similarity.
- Does not detect AI-written text.
- The API ships without authentication.
- Hosted Free allows three checks per month.
The verdict
Noplag Engine focuses on verbatim and near-verbatim matching, with local-corpus deployment or additional live-web search in the hosted product. Its stated detection limits and unauthenticated API are worth considering before use.
Who it suits
The maker positions Free for trying the service or self-hosting, Pro for makers and small teams, Premium for agencies and publishers, and Enterprise for universities and regulated organizations. The tool may suit users who need matching against a controlled corpus and can work within its detection limits.
Plans and prices
Free
2,500 words per check · public web + Common Crawl · self-host for unlimited local checks
Read 29 Sep 2026 · noplag.com
Pro
50 checks per month · 25,000 words per check · Noplag Database · academic index
Read 29 Sep 2026 · noplag.com
Premium
200 checks per month · 50,000 words per check · Live Web search · branded PDF reports
Read 29 Sep 2026 · noplag.com
Enterprise
Custom check volume · all corpora + Live Web · on-prem or private cloud · SSO/SAML
Read 29 Sep 2026 · noplag.com
On the record
- API
- The engine exposes a `/v1` API with checks, reports, uploads, progress events, and corpus management, and ships without authentication.github.com · read 29 Sep 2026
- Corpus
- The open-source engine searches a local corpus, while the hosted product additionally searches the live web.github.com · read 29 Sep 2026
- Detection limits
- The engine does not detect paraphrase, semantic similarity, or AI-written text; the README describes those capabilities as roadmap work.github.com · read 29 Sep 2026
- Input and ingestion
- The engine supports corpus ingestion from .txt, .md, .pdf, and .docx files, including folder ingestion and HTTP file upload.github.com · read 29 Sep 2026
- Integrations
- The Enterprise plan lists Canvas, Moodle, and Blackboard LMS integrations; the features page also names Brightspace via LTI 1.3.noplag.com · read 29 Sep 2026
- Languages
- The hosted product says detection is calibrated for English, Spanish, Portuguese, Polish, and Ukrainian at launch.noplag.com · read 29 Sep 2026
- License and deployment
- The engine is licensed under Apache 2.0 and can be run on the user's own hardware with Docker Compose.github.com · read 29 Sep 2026
- Matching
- The engine uses winnowing fingerprints to retrieve candidate sources and a seed-and-extend aligner to locate matching character ranges.github.com · read 29 Sep 2026
- Privacy
- The maker says submitted documents are never used to train models; hosted-plan retention is configurable and EU data residency is available on request.noplag.com · read 29 Sep 2026
- Purpose
- Noplag Engine is an open-source plagiarism detection engine for verbatim and near-verbatim matching against a corpus you control.github.com · read 29 Sep 2026
- Reports
- Reports include per-source similarity, matching passage offsets, and coverage accounting.github.com · read 29 Sep 2026
- Runtime requirements
- The repository says development requires Python 3.12 or newer and uses PostgreSQL in its Docker Compose setup.github.com · read 29 Sep 2026
- Who it serves
- The maker positions Free for trying the service or self-hosting, Pro for makers and small teams, Premium for agencies and publishers, and Enterprise for universities and regulated organizations.noplag.com · read 29 Sep 2026
