AN HONEST COMPARISON
Noplag vs Copyleaks
Two API-first detectors targeting developers and SMBs. We'll be specific about where Copyleaks is genuinely better — and where the open-source approach pulls ahead.
noplagOpen-source, since 2014OUR SIDE
CopyleaksAPI-first, since 2015THE PEER
Choose Noplag if
- You want flat-rate pricing — no monthly credit expiry
- You need API access with predictable cost at variable workloads
- You want to read the detection algorithm (Apache 2.0 source on GitHub)
- You need to self-host — Copyleaks is SaaS-only
- You want documents you submit to stay erasable from any internal database
- You want per-language ESL-bias calibration data, not a single 3% claim
Choose Copyleaks if
- You need Codeleaks-level code-plagiarism detection (100+ programming languages)
- Your LMS isn't on Noplag's v1.2 roadmap (Schoology, Sakai, Edsby — Copyleaks only)
- Multilingual coverage matters and you scan in less-common languages (100+ vs our launch set of 5)
- You're already deeply embedded in the Copyleaks API and can absorb the credit-expiry cost
- You need the 'High / Medium / Low' AI-verdict UI for non-technical reviewers
- You want AI-generated source-code detection (Codeleaks supports 40+ languages)
FEATURE COMPARISON
The actual differences, line by line.
ACCESS & PRICING
Individual access
NOPLAGYes — sign up in 30 seconds
COPYLEAKSYes — sign up in 30 seconds
Pricing model
NOPLAGFlat-rate subscription
COPYLEAKSCredit-based + flat-rate plans
Free tier
NOPLAG2,500 words per check, forever
COPYLEAKSTrial only · 20 credits, then upgrade
Per-use cost
NOPLAG$23/mo Pro · $79/mo Premium · self-host free
COPYLEAKS$13.99/mo Personal · $74.99/mo Pro · 1 credit = 250 words
Self-serve onboarding
NOPLAGCredit card · self-serve
COPYLEAKSCredit card · 30 seconds
DETECTION & ACCURACY
Auditable algorithm
NOPLAGApache 2.0 source on GitHub
COPYLEAKSClosed source
Open-web check
NOPLAGGoogle + Brave
COPYLEAKSYes (their crawl + Common Crawl)
Academic database
NOPLAGCORE + OpenAlex + arXiv + 5 more (150M papers)
COPYLEAKSProprietary academic-journal + books index
Code-plagiarism product
NOPLAGNo — not in v1 scope
COPYLEAKSCodeleaks — 100+ languages, 99.8% accuracy claim
False-positive rate (independent tests)
NOPLAGMeasured against PAN-PC-11 in CI
COPYLEAKSF1 = 0.87 on independent 2,500-sample benchmark (2025)
AI-CONTENT DETECTION
AI detection available
NOPLAGComing soon · v1.2 roadmap
COPYLEAKSYes · included across all paid tiers
Detection method
NOPLAGBinoculars ensemble (open paper)
COPYLEAKSProprietary classifier
ESL-bias safeguard documented
NOPLAGYes · per-language eval + disclaimer
COPYLEAKSClaimed ~3% ESL bias; methodology not published
Reported as 'signal' vs 'verdict'
NOPLAGSignal — per-sentence transparency
COPYLEAKS'High / Medium / Low' verdict labels in LMS reports
PRIVACY & DATA
Documents used to train models
NOPLAGNever
COPYLEAKSStored permanently in 'Shared Data Hub' · used for cross-submission matching
Right-to-erasure (GDPR)
NOPLAGOne-click in Settings
COPYLEAKSInternal-database submissions cannot be removed once added
EU data residency
NOPLAGAvailable · Pro+
COPYLEAKSAvailable · enterprise tier
Self-host option
NOPLAGYes · Apache 2.0 engine
COPYLEAKSNo · SaaS only
DEVELOPERS & INTEGRATIONS
Public REST API
NOPLAGYes · OpenAPI spec, $23/mo Pro
COPYLEAKSYes · credit-based · all tiers
Webhooks
NOPLAGYes · Pro+
COPYLEAKSYes · all tiers
LMS integrations
NOPLAGCanvas + Moodle (v1.1, 4 by v1.2)
COPYLEAKSCanvas, Brightspace, Moodle, Blackboard, Schoology, Sakai, Edsby (7) + Teams
Multilingual coverage
NOPLAGDetection for EN, ES, PT, PL, UK at launch, expanding
COPYLEAKS100+ languages claimed
| Feature | NOPLAG | COPYLEAKS |
|---|---|---|
| ACCESS & PRICING | ||
| Individual access | Yes — sign up in 30 seconds | Yes — sign up in 30 seconds |
| Pricing model | Flat-rate subscription | Credit-based + flat-rate plans |
| Free tier | 2,500 words per check, forever | Trial only · 20 credits, then upgrade |
| Per-use cost | $23/mo Pro · $79/mo Premium · self-host free | $13.99/mo Personal · $74.99/mo Pro · 1 credit = 250 words |
| Self-serve onboarding | Credit card · self-serve | Credit card · 30 seconds |
| DETECTION & ACCURACY | ||
| Auditable algorithm | Apache 2.0 source on GitHub | Closed source |
| Open-web check | Google + Brave | Yes (their crawl + Common Crawl) |
| Academic database | CORE + OpenAlex + arXiv + 5 more (150M papers) | Proprietary academic-journal + books index |
| Code-plagiarism product | No — not in v1 scope | Codeleaks — 100+ languages, 99.8% accuracy claim |
| False-positive rate (independent tests) | Measured against PAN-PC-11 in CI | F1 = 0.87 on independent 2,500-sample benchmark (2025) |
| AI-CONTENT DETECTION | ||
| AI detection available | Coming soon · v1.2 roadmap | Yes · included across all paid tiers |
| Detection method | Binoculars ensemble (open paper) | Proprietary classifier |
| ESL-bias safeguard documented | Yes · per-language eval + disclaimer | Claimed ~3% ESL bias; methodology not published |
| Reported as 'signal' vs 'verdict' | Signal — per-sentence transparency | 'High / Medium / Low' verdict labels in LMS reports |
| PRIVACY & DATA | ||
| Documents used to train models | Never | Stored permanently in 'Shared Data Hub' · used for cross-submission matching |
| Right-to-erasure (GDPR) | One-click in Settings | Internal-database submissions cannot be removed once added |
| EU data residency | Available · Pro+ | Available · enterprise tier |
| Self-host option | Yes · Apache 2.0 engine | No · SaaS only |
| DEVELOPERS & INTEGRATIONS | ||
| Public REST API | Yes · OpenAPI spec, $23/mo Pro | Yes · credit-based · all tiers |
| Webhooks | Yes · Pro+ | Yes · all tiers |
| LMS integrations | Canvas + Moodle (v1.1, 4 by v1.2) | Canvas, Brightspace, Moodle, Blackboard, Schoology, Sakai, Edsby (7) + Teams |
| Multilingual coverage | Detection for EN, ES, PT, PL, UK at launch, expanding | 100+ languages claimed |
PRICING REALITY
What you'll actually pay.
Copyleaks sells subscription credits — 1 credit covers up to 250 words, credits do not carry over month-to-month. Noplag is flat-rate — pay once a month, scan up to your tier limit. The Copyleaks math below uses their published 2026 plan prices.
noplagMOST FLEXIBLE
- Free / self-host$0Apache 2.0 forever
- Pro$23/moyearly · 500 pages/mo
- Premium$79/moyearly · 5,000 pages/mo
- EnterpriseCustomannual · unlimited pages
CopyleaksAPI-FIRST
- Free trialFree20 credits · expires
- Personal$13.99/mo100 credits/mo · 25k words
- Pro$74.99/mo1,000 credits/mo · 250k words
- EnterpriseCustomVolume-based · sales-led
Copyleaks pricing from copyleaks.com/pricing (2026). Unused credits expire each month and do not carry over — a real cost factor at variable workloads.
MIGRATING FROM COPYLEAKS
Drop-in API compatibility.
If you're using Copyleaks via API, migration is mostly a base-URL swap and field-name remapping. Our OpenAPI spec ships with a compatibility table covering Copyleaks's most-used endpoints; webhook payloads can be auto-translated by the proxy we publish as a Docker image. Teams also commonly migrate to escape the monthly credit-expiry cycle — Noplag's flat-rate tiers don't charge variable usage. Most dev teams migrate in under a week.
Read the API migration guideFREQUENTLY ASKED
Questions from teams migrating from Copyleaks.
- Is Noplag as accurate as Copyleaks?
- On open-web and academic content, accuracy is comparable — both products scan similar source categories. Copyleaks also maintains a 'Shared Data Hub' that stores prior submissions for cross-checking, which catches student-to-student copying within your institution; submissions to this DB cannot be removed once added. Noplag's equivalent is the Noplag Database (anonymized fingerprints, not full text), which submissions join by default — you can opt out and turn it off, and erasure rights apply either way.
- Can I migrate from Copyleaks API to Noplag?
- Yes — the migration is mostly a base-URL swap plus field-name remapping. Our /docs/migrating-from-copyleaks page maps every Copyleaks API endpoint to the Noplag equivalent. Webhooks are payload-compatible via a translation proxy we ship as a Docker image.
- What about Copyleaks's code-plagiarism (Codeleaks)?
- This is a real gap for us. Codeleaks is Copyleaks's code-plagiarism product — 100+ programming languages for plagiarism, 40+ for AI-generated-code detection, with claimed 99.8% accuracy, license detection, and GitHub PR integration. If code-plagiarism is your primary use case, Codeleaks is the right tool. For text-content checking with developer-friendly tooling, the comparison flips toward Noplag.
- Does Noplag work with my LMS?
- Canvas and Moodle ship in v1.1 (Q4 2026). Blackboard and D2L on the v1.2 roadmap. Copyleaks currently ships 7 LMS integrations including Schoology, Brightspace, and ATutor — if you're on one of those and integration is the top priority, Copyleaks is the right tool today. Noplag will close the gap on the most-requested four by v1.2.
- How is Noplag's AI detection different from Copyleaks's?
- Copyleaks ships an AI detector today that scored F1 = 0.87 on an independent 2,500-sample 2025 benchmark — roughly 90% on raw AI text, dropping to ~25% on humanized text. They report scores with 'High / Medium / Low' verdict labels and claim ~3% ESL false-positive bias (methodology not published). Noplag's AI detection is coming soon (on the v1.2 roadmap, not live at launch): when it ships, we'll publish per-language calibration data, surface explicit ESL-writer disclaimers, and report AI-likelihood as a signal with confidence intervals — not a verdict. Our classifier will be auditable via the open-source repo.
- Can I self-host Noplag for sensitive documents?
- Yes — the detection engine is Apache 2.0 and runs in Docker. Enterprise customers get the cloud corpus shipped as an indexable bundle. Copyleaks does not currently offer a self-host option; if data sovereignty or air-gap deployment is a hard requirement, Noplag is the only fit between the two.
- How long does API migration take?
- For API-only migration: day 1 — base URL swap + endpoint mapping; days 2–3 — webhook compat shim; days 4–5 — parallel-run validation; week 2 — cutover. For LMS-deployed Copyleaks instances, factor an additional 2–4 weeks for plugin retraining and stakeholder communication.
- What about Copyleaks's GitHub / dev-tool integrations?
- Copyleaks integrates with GitHub Actions, Bitbucket Pipelines, and a handful of other dev tools. Noplag's developer integrations focus on the API + webhook surface; if you need a GitHub-Action-level workflow, you can wire it up via the API in about 30 lines of YAML — but it's not a packaged integration we maintain. Trade-off: less polish, more flexibility.
Run a side-by-side check against your Copyleaks setup.
Drop in a document you've already checked with Copyleaks. Compare the reports. Free, no signup. You'll know in 60 seconds whether the open-source angle, the API surface, and the ESL-honesty matter for your use case.