Overview

Noplag is an open-source plagiarism checker with a hosted service for people who need to inspect and document direct text overlap. It suits writers, publishers, and education teams whose priority is source-linked evidence; its current matching does not cover paraphrase, and AI-content detection is not yet available.

The checker accepts documents, pasted text, and URLs, then returns matched passages with their sources and a similarity score. That makes it useful for reviewing likely copying rather than treating a score alone as a conclusion.

For broader comparisons, see Plagiarism Checkers, Plagiarism Detection Software, and AI Plagiarism Checkers.

Key features

Matching and reports

Noplag’s live engine uses winnowing fingerprints and live-web matching to find verbatim and near-verbatim copying. It checks against the open web, Common Crawl, Wikipedia, academic indexes, the Noplag Database, and users’ own folders. The breadth is useful for direct-overlap checks, though it does not change the central limitation: paraphrased material is outside the current engine’s scope.

Reports connect each match to its source and show the overlapping text alongside a similarity score. PDF export gives users a shareable record, a practical advantage for editorial review or institutional follow-up.

Submission, language, and integrations

Users can upload DOCX, PDF, TXT, ODT, or RTF files, paste text, or submit a URL. Detection is calibrated for English, Spanish, Portuguese, Polish, and Ukrainian. Canvas, Moodle, Blackboard, and Brightspace integrations are offered through LTI 1.3, making the product more relevant to education teams than a standalone checker without LMS connections.

The REST API, OpenAPI specification, and webhooks are available on paid tiers. That gives developers and teams a route to connect checks to their own workflows, but API access is not part of the free offer.

Privacy and security

Noplag says submitted documents are not used to train models or shared between accounts, and EU data residency is available. It encrypts data in transit and at rest, but does not yet hold formal attestations such as SOC 2—a meaningful consideration for organizations with procurement or compliance requirements.

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 time limit. Support ranges from community Discord on Free to email on Pro and priority support with a 12-hour response target on Premium.

Pricing

Noplag has a free tier, a 14-day trial, and paid plans starting at 9.99 USD per month. The free plan allows 3 checks per month, up to 2,500 words per check, and searches the public web and Common Crawl; support is through community Discord. It is a modest way to check occasional short submissions, but its monthly quota and word cap will constrain regular use.

Pro costs 9.99 USD per month and includes 50 monthly checks of up to 25,000 words each, plus the Noplag Database, academic index, REST API, webhooks, and email support. Noplag positions it for makers and small teams. Compared with Free, it adds substantially more capacity and research-oriented sources, but it does not include the Live Web search or branded reports listed for Premium.

Premium costs 19.99 USD per month. It raises the allowance to 200 checks monthly and 50,000 words per check, adds Live Web search and branded PDF reports, and includes priority support with a 12-hour response target. This better fits agencies and publishers handling larger volumes or client-facing reports.

Enterprise has custom pricing, custom check volume, all corpora plus Live Web search, on-premises or private-cloud deployment, SSO/SAML, LMS integrations, and dedicated support with an SLA. It is aimed at universities and regulated organizations that need deployment and administration options beyond the fixed tiers.

Platforms

Noplag supports web, Windows, macOS, Linux, API, and self-hosted deployments. The combination of hosted access, API, and self-hosting gives teams more deployment paths than a web-only checker, while the API is reserved for paid tiers.

Who it's for

Noplag is a sensible fit for writers and small teams that need periodic, source-linked checks, and for publishers or schools that need higher quotas, PDF reporting, or LMS workflows. It is a weaker choice for anyone who needs paraphrase detection, needs AI-content screening now, or requires formal security attestations such as SOC 2.

Pros and cons

Pros: Matches link to sources and expose exact overlapping text, so reviewers can inspect the basis for a flag.
Pros: PDF reports, academic sources, API access, and LMS integrations support editorial and institutional workflows.
Pros: Paid retention choices and EU data residency offer useful controls for organizations handling documents.
Cons: The current engine does not detect paraphrase, limiting its usefulness for checks that must catch rewritten material.
Cons: AI-content detection is still coming soon, so it cannot serve as a current AI-screening tool.
Cons: The Free tier’s 3 monthly checks and 2,500-word cap leave little room for frequent or long-document review.
Cons: Noplag does not yet hold formal attestations such as SOC 2, which may rule it out for some regulated buyers.

Alternatives

PrePostSEO Plagiarism Checker is worth considering if Android or iOS access matters; its Basic all-in-one annual plan is 4.17 USD per year, billed $50 billed annually, and allows 5K words per submission.

Smodin Plagiarism Checker may suit users who want plagiarism checking alongside a broader set of AI tools; its Starter plan is 10.00 USD per month, billed annually.

PlagAware is another freemium option, with web and API access; its free plan covers 10 pages per month and up to 30 monitored URLs with a Content Protection Banner.

SmallSEOTools Plagiarism Checker may fit occasional short scans on a free plan, which allows up to 1,000 words per scan.

Copyscape is an alternative for URL-based checking; its free scans are limited per website and return up to 10 results per search.

Originality.ai is the more relevant alternative when AI detection is the priority: its free Basic plan is AI detection only, with 3 scans per day and a 2,000-word limit per scan.

Plagiarism Checker X may suit Windows users who prefer a one-time purchase; its Professional plan costs 39.95 USD per user license, paid once for use forever.

Quetext AI Detector is another freemium option combining AI detection and plagiarism-checking tools, with its free plan capped at 1,000 words for each of those checks.

Verdict

Choose Noplag if you need direct-copy matching with source links, readable overlap evidence, PDF export, and a path from occasional checks to institutional deployment. Look elsewhere if paraphrase detection or current AI-content screening is essential; those gaps define the limits of its otherwise useful reporting workflow.

	Noplag	Winston AI
Free plan	Yes	Yes
Free trial	Yes	Yes
Paid from	$9.99/mo	$5/mo
Open source	No	No
Platforms	api, Linux, macOS, self-hosted, Web, Windows	api, extension, Web
Free plan	Yes	No
API access	Yes	Yes
Browser extension	—	Yes

Noplag vs Winston AI

Noplag

Winston AI