copydetect

Overview

Copydetect is a free, Python-based tool for comparing code directories and producing reports of matching code. It suits educators and developers who want configurable, repository-level checks without a hosted subscription. Its results are useful leads for investigation, but they cannot establish plagiarism or reliably catch deliberate evasion.

Key features

Copydetect uses Winnowing document fingerprinting, an approach also used by MOSS, and Pygments tokenization to handle more than 500 languages that Pygments can detect and tokenize. That breadth makes it practical for mixed-language coursework or repositories; it does not remove the need to review matches in context.

The command-line tool recursively compares files in supplied directories; its simplest invocation is copydetect -t DIRS. Separate reference directories let users compare submissions with earlier work, while boilerplate directories can exclude shared starter code. This is a useful distinction for course workflows, where a common template should not dominate the report.

Filtering replaces variable, function and object names, and strings with token markers, shifting comparison away from those surface differences. Noise, guarantee and display thresholds let users tune detection and report visibility. Settings can be passed as command-line arguments or through a JSON configuration file, which supports repeatable configurations but requires users to choose appropriate thresholds.

The Python API includes CopyDetector, CodeFingerprint, compare_files and HTML report generation. Reports can be written to a chosen path, highlighted code can be truncated, and custom CSS can be linked. The package installs with pip and requires Python 3.7 or later. Copydetect is MIT-licensed, operating-system independent, and classified for Education and as a Beta project.

Pricing

Copydetect is free software under the MIT License, with no free trial. There are no paid tiers or seat and scan quotas in its stated pricing model, making it suitable where a team can install and operate the package itself. The trade-off is that this is a package and API, not a paid managed service.

Platforms

Copydetect is classified for Linux, macOS and Windows, as well as API and self-hosted use. It is Python 3 only and requires Python 3.7 or later. Those requirements suit users comfortable with Python installation and command-line workflows; readers seeking an IDE plugin or CI integration should look elsewhere, as neither is supported.

Who it's for

Educators comparing submissions, and developers checking repositories against reference code, are the clearest fit. Its configurable exclusions and report controls help when comparisons need to account for boilerplate or different review thresholds. It is a poor fit as a standalone verdict system: matching code is evidence to inspect, not proof of copying, and the project does not guarantee detection when someone deliberately evades it.

Pros and cons

• Pros: Pygments language coverage spans more than 500 tokenizable languages, so users are not confined to a short list of common programming languages.
• Pros: Reference and boilerplate directories support comparisons that distinguish prior work and shared starter code from the test material.
• Pros: Thresholds, JSON configuration and customizable HTML reports provide control over how comparisons are run and presented.
• Cons: Detection is not guaranteed against deliberate evasion, and a match cannot prove plagiarism; human review remains essential.
• Cons: Python 3.7 or later and command-line or API use make it less suitable for users who want an IDE-integrated or CI-integrated workflow.
• Cons: Beta development status is a caveat for institutions that need a mature, supported system.

Alternatives

Code Clone Detection Tools is the broader category directory for readers comparing clone-detection options.

Duplo is a free alternative for Linux, macOS and Windows users who want software distributed under GNU GPL v2 or later, with prebuilt binaries for Alpine Linux, macOS and Windows.

Hound is a free alternative with API, self-hosted and web platform options as well as Linux and macOS support.

PMD is a free, BSD-style-licensed static code analyzer for Linux, macOS, Windows and self-hosted use.

Simian Similarity Analyzer is a free, open-source option under the Apache License 2.0 for Linux, macOS and Windows.

CloneWorks is free on Linux, macOS and Windows, but its license requires acknowledgement and that redistribution and derivatives remain free of charge.

dcd is a free AGPL-3.0 option for Linux and macOS; it also offers priority direct email support at custom pricing.

jscpd is a free alternative available for API, self-hosted and web use, as well as Linux, macOS and Windows.

Algo VPN is another free option, with Android, iOS, Linux, macOS and Windows support.

Verdict

Choose copydetect if you need a free, configurable way to compare code directories across many tokenizable languages, especially for education or reference-based review. Its main advantage is the combination of directory controls, filtering and adjustable HTML reporting; look elsewhere if you need integrated CI or IDE workflows, or a tool that can deliver a definitive plagiarism finding.