Noplag

Overview

Noplag is an open-source plagiarism checker with a hosted service, best suited to people who need to trace verbatim or near-verbatim overlap across web and academic sources. Source-linked reports and a free allowance make it a practical starting point, but its inability to detect paraphrase is a decisive limitation for broader integrity checks.

Founded in 2014 and headquartered in San Francisco, Noplag releases its checking engine under Apache 2.0. The live engine uses winnowing fingerprints and live-web matching. MinHash LSH and vector reranking are future releases, not part of the current matching workflow.

Submissions can be DOCX, PDF, TXT, ODT, or RTF files, pasted text, or a URL. Matching sources include 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 connect each match to its source and show a similarity score alongside the exact overlapping text; PDF export is available. That evidence is more useful for review than a score alone, though it does not solve the checker’s blind spot for rewritten material. AI-content detection is coming soon and is intended as a separate signal.

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

Key features

Matching and reports

Noplag’s mix of web, academic, and user-supplied sources suits checks for direct reuse across different kinds of material. The source links and highlighted overlap let a reviewer inspect why a passage matched, while PDF export is useful when findings need to be shared. The trade-off is scope: the current engine identifies verbatim and near-verbatim copying, not paraphrase, so it should not be the sole check when substantial rewriting is a concern.

Submission and language coverage

File uploads, pasted text, and URL submission offer flexibility for writers and teams working with different source formats. Five launch languages—English, Spanish, Portuguese, Polish, and Ukrainian—make the checker relevant to some multilingual workflows, but the calibrated coverage is limited to those languages.

Integrations, privacy, and security

The features page lists Canvas, Moodle, Blackboard, and Brightspace integrations through LTI 1.3. The REST API, OpenAPI specification, and webhooks can support custom workflows, with API access reserved for paid tiers. Noplag says 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 formal assurance requirements.

Free-tier document content is purged 30 days after a check. Paid users can choose a 30-, 60-, or 90-day retention window, while Enterprise can retain content without limit. Free users receive community Discord support, Pro email support, and Premium priority support with a 12-hour response target.

Pricing

Noplag is freemium, with a free plan, paid plans from $9.99/mo, and a 14-day trial. The free tier is useful for occasional short checks; regular or institutional use will quickly require a paid plan because its monthly allowance is small.

Free gives up the Noplag Database and academic index found on Pro, and its per-check word cap is one tenth of Premium’s. Pro adds those corpora and API access, but does not include Premium’s Live Web search, branded reports, or priority response target. Premium is the step up for high-volume checking and branded output; Enterprise is the only stated option for custom volume and private deployment.

Platforms

Noplag supports web, Windows, macOS, Linux, API, and self-hosted deployments. That spread gives technical teams options beyond the hosted web workflow; on-premises or private-cloud deployment is specifically part of Enterprise.

Who it's for

Noplag is a sensible fit for writers, publishers, small teams, and schools that need evidence of close textual overlap, especially when academic sources or source-linked PDF reports matter. Its tier structure also provides a route from a few free checks to API-enabled workflows and institutional deployment. It is a poor fit as a standalone safeguard against paraphrasing or as an AI-writing detector today; the latter capability is still coming soon.

Pros and cons

• Pros: Source links, similarity scores, and exact overlapping text make matches reviewable rather than opaque.
• Pros: File, pasted-text, and URL submissions cover several common checking workflows, with PDF report export for sharing.
• Pros: Paid plans expand corpus access, API capability, volume, integrations, and deployment choices for different organizational needs.
• Cons: The current engine does not detect paraphrase, leaving a substantial gap for checks where meaning-preserving rewrites matter.
• Cons: Free is capped at three monthly checks and 2,500 words per check, and lacks academic-index and Noplag Database matching.
• Cons: AI detection is not yet available, and the service does not yet hold formal security attestations such as SOC 2.

Alternatives

Choose PrePostSEO Plagiarism Checker if broad device coverage, including Android and iOS, is more important than Noplag’s stated source-linked matching workflow; it also offers a free plan.

Smodin Plagiarism Checker is another freemium option, with Android, iOS, web, API, and extension platforms; its Starter plan includes checking against web and academic sources, while Premium includes all AI tools.

Pick Originality.ai when AI detection is the priority: its Basic plan is AI detection only, while its listed platforms include web, API, and extension. For a no-subscription option, that plan offers three scans per day up to 2,000 words per scan.

PlagAware is worth considering for its web and API availability and a free allowance of 10 pages per month, including monitoring of up to 30 URLs with a Content Protection Banner.

Plagiarisma offers a free Windows desktop plagiarism checker, making it an alternative for Windows users seeking a desktop option.

Choose PlagiarismCheck.org if paying per checked pages without monthly fees better suits your usage; it offers API, extension, and web access.

PlagiarismSearch offers a freemium service and a one-time Light package with one plagiarism submission and one AI submission; it also supports API, extension, and web access.

Quetext AI Detector bundles an AI detector and plagiarism checker in its free plan, each up to 1,000 words, and adds summarizer and humanizer allowances; it supports API, extension, and web access.

Verdict

Choose Noplag for source-linked evidence of verbatim and near-verbatim copying, particularly if you need academic matching, PDF reports, or a path to API and institutional deployment. Its free plan is a useful small-scale starting point, and paid tiers add clear capacity and workflow options. Look elsewhere if paraphrase detection or current AI-content screening is essential, or if formal security attestations are a prerequisite.