Noplag

Overview

Noplag is an open-source plagiarism checker with a hosted cloud service, suited to writers, publishers, and schools that need source-linked reports on copied text. Its useful core is evidence you can inspect and export; it is less suitable when paraphrase detection or AI-content screening is central.

The checker accepts DOCX, PDF, TXT, ODT, and RTF files, pasted text, or URLs. Its live engine uses winnowing fingerprints and live-web matching to find verbatim and near-verbatim overlap. Comparisons draw on the open web, Common Crawl, Wikipedia, academic indexes, the Noplag Database, and users’ own folders. Detection is calibrated for English, Spanish, Portuguese, Polish, and Ukrainian.

Reports link matches to sources and show both a similarity score and the exact overlapping text, with PDF export. That makes it easier to review why a passage was flagged rather than treating a score as a verdict. The boundary matters: the current engine does not detect paraphrase, and AI-content detection is still coming soon as a separate signal.

Noplag was founded in 2014 and is headquartered in San Francisco. Its engine is released under Apache 2.0, while the hosted service supplies the checking workflow and paid features.

Key features

Matching and reports

The source mix is a strength for direct-copy checks: users can compare against general web material, academic indexes, the Noplag Database, and private folders. Source links and displayed overlap support manual review, while PDF export is useful for sharing findings. Near-verbatim matching broadens coverage beyond exact strings, but this is not a substitute for paraphrase analysis.

Uploads, integrations, and API

Multiple document formats, pasted text, and URL submission accommodate different workflows. Canvas, Moodle, Blackboard, and Brightspace integrations use LTI 1.3, making Noplag more relevant to institutional workflows than a standalone checker. The REST API includes an OpenAPI specification and webhooks, but access is limited to paid tiers.

Privacy and security

Noplag says submissions are not used to train models or shared between accounts, and offers EU data residency. It encrypts data in transit and at rest, but does not yet hold formal attestations such as SOC 2. Free-tier document content is purged 30 days after a check; paid users can choose 30-, 60-, or 90-day retention, while Enterprise can retain content without a limit. Organizations with formal assurance requirements should weigh the absence of attestations alongside these stated controls.

Pricing

Noplag is freemium, with a 14-day trial and paid plans from $9.99/mo. The free plan is unusually constrained for recurring work: three checks per month and 2,500 words per check, with public web and Common Crawl matching only. Community Discord support is the tradeoff. It can suit occasional short checks, but not sustained classroom or editorial screening.

Pro costs 9.99 USD per month and raises capacity to 50 checks per month and 25,000 words per check. It adds the Noplag Database, academic index, REST API and webhooks, plus email support. This is the practical starting point for makers and small teams that need academic sources or automation without Premium-level volume.

Premium costs 19.99 USD per month, with 200 checks monthly and a 50,000-word ceiling per check. It adds Live Web search, branded PDF reports, and priority support with a 12-hour response target. Agencies and publishers that need higher throughput or client-ready reports have a clearer reason to pay; occasional users will likely not use the extra quota.

Enterprise has custom pricing and custom check volume, with all corpora and Live Web search, on-premises or private-cloud deployment, SSO/SAML, LMS integrations, and dedicated support with an SLA. It is positioned for universities and regulated organizations needing deployment and access controls that individual plans do not provide.

Platforms

Noplag supports web, API, Linux, macOS, Windows, and self-hosted deployment. The combination of hosted access, API, and private deployment options serves both individual checking and institutional integration needs, though the API is a paid feature and self-hosting is an Enterprise deployment option.

Who it's for

Noplag fits writers, small teams, agencies, publishers, and educational organizations whose primary concern is locating direct or near-direct textual overlap and reviewing its sources. The free tier is best reserved for light use; Pro suits makers and small teams, Premium suits agencies and publishers, and Enterprise targets universities and regulated organizations.

Look elsewhere if your main requirement is catching rewritten or paraphrased material, or if you need AI-content detection now. The planned AI signal should not be treated as a current capability.

Pros and cons

Pros

• Traceable findings: source links, similarity scores, and exact overlapping passages make reports more actionable than an unexplained score.
• Broad submission options: common document formats, pasted text, and URLs cover several input workflows.
• Academic and institutional fit: academic indexes, LMS integrations, API access, and Enterprise deployment options support more than personal checks.
• Retention choices: paid users can set 30-, 60-, or 90-day windows, with unlimited retention available for Enterprise.

Cons

• No paraphrase detection: rewritten copying can fall outside the current engine’s stated scope.
• AI detection is not ready: it is a planned separate signal, not a present screening tool.
• Free capacity is tight: three checks a month and 2,500 words per check limit regular or longer-document use.
• Formal assurance gap: Noplag does not yet hold attestations such as SOC 2, a concern for organizations that require them.

Alternatives

Choose Smodin Plagiarism Checker if Android or iOS access matters, or if a bundle of AI tools alongside web and academic plagiarism checking better fits your workflow; its Starter plan is 10.00 USD per month billed annually.

PlagAware is an alternative with a free plan covering 10 pages per month and monitoring for up to 30 URLs with a Content Protection Banner. Its Subscription Light plan costs 2.99 EUR per month.

Consider PlagiarismCheck.org if you prefer pay-per-page pricing without monthly fees: its Basic plan is 5.99 USD per once for 20 pages.

PlagiarismSearch offers a one-time Light package at 9.95 USD for one plagiarism submission and one AI submission, which may suit a one-off check better than Noplag’s recurring quota plans.

PrePostSEO Plagiarism Checker is another freemium option, with a Basic all-in-one annual plan at 4.17 USD per year, billed as $50 annually.

Quetext AI Detector has a free plan that includes an AI detector and plagiarism checker for up to 1,000 words each, making it a relevant alternative for short checks that need both signals.

Originality.ai offers a free AI-detection-only plan with three scans per day and a 2,000-word limit per scan; choose it when AI screening, rather than Noplag’s source-linked plagiarism reports, is the priority.

Plagiarisma is an alternative with a free Windows desktop plagiarism checker.

Compare more options in Plagiarism Checkers, AI Plagiarism Checkers, and Plagiarism Detection Software.

Verdict

Noplag is a sensible choice for users who need traceable evidence of verbatim and near-verbatim overlap, especially when academic sources, LMS integrations, or API workflows matter. Its source-linked reports are the main reason to choose it; the lack of paraphrase detection is the main reason to look elsewhere. The free plan works for occasional short checks, while regular teams should compare Pro or Premium quotas against their monthly volume.