Copyleaks AI Detector vs Noplag Engine

Copyleaks AI Detector identifies AI-written text, including writing that mixes AI and human passages. It supports more than 30 languages and names GPT-5, GPT-4, ChatGPT, Claude, Gemini, DeepSeek, Llama, Bloom, Rytr, and Jasper among the sources it detects. AI Logic explains flagged results, displays AI phrase frequency, and can identify text appearing in published content elsewhere. The web detector scans up to 25,000 characters without login; the website platform requires at least 255 characters and accepts up to 2,000 pages. A Chrome and Edge extension accepts 350 to 25,000 characters, and a Google Docs add-on and education LMS integrations connect it to other workflows. Personal costs $13.99 a year with annual billing or $16.99 a month; Pro costs $74.99 a year with annual billing or $99.99 a month. A free plan and free trial are listed. Copyleaks says data is encrypted at rest with AES-256, reports SOC 2 and SOC 3 certifications, and supports GDPR compliance.

Noplag Engine is an open-source plagiarism detection tool that checks text for verbatim and near-verbatim matches against a corpus you control. It uses winnowing fingerprints to find candidate sources, then aligns matching character ranges. Reports show similarity by source, passage offsets, and coverage accounting. It accepts.txt,.md,.pdf, and.docx files, with folder ingestion and HTTP uploads, and exposes a /v1 API for checks, reports, uploads, progress events, and corpus management. The API 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 can run on your own hardware with Docker Compose under the Apache 2.0 license. The repository lists Python 3.12 or newer for development and PostgreSQL in its Docker Compose setup. The free hosted plan costs nothing and allows 3 checks per month, while self-hosting permits unlimited local checks. Pro costs $9.99 a month and Premium costs $19.99 a month; Enterprise pricing is custom.