dcd

Overview

dcd is a free, open-source duplicate-code detector for repository-scale analysis. It suits developers and engineering teams that need to tune what counts as a clone, inspect duplication visually, and feed findings into automation. Its text-based approach and broad language parsing make it practical for many codebases, while Windows support requires a workaround.

The project is released under the GNU Affero General Public License 3.0 and is available as a self-hosted command-line tool. Ben Boyter, a professional software engineer with more than 15 years of development experience focused on testing, is the developer behind it.

Key features

dcd uses text clone detection with language-aware parsing through scc for more than 250 languages. That breadth is valuable for repositories containing several languages, although parsing coverage does not turn the tool into an IDE assistant: there is no IDE integration.

The --fuzz option uses simhash distance to find similar but non-identical lines, with values from 0 to 255. Lower or higher settings let a team choose between stricter matches and broader near-duplicate discovery, but the setting needs deliberate tuning to avoid noisy results.

--gap-tolerance bridges inserted, deleted, or modified lines inside otherwise matching duplicate blocks. --max-hole-size allows modified lines within a duplicate diagonal match. Together, these controls are useful when copied code has drifted, rather than remaining an exact block. The --file option compares one file with the rest of the codebase, making focused investigations faster than starting with a full repository comparison.

For visual review, dcd creates PBM scatter plots and self-contained interactive HTML reports containing file heatmaps and scatter plots. Those outputs help reviewers see concentration and distribution of clones instead of relying only on text listings. The --format json option produces structured output for other tools and CI pipelines, and CI integration is supported.

Ignore files use the same syntax as .gitignore files, and dcd can ignore marked code blocks. This is important for excluding generated or intentionally repeated sections without weakening the matching rules for the rest of a scan.

Pricing

The dcd plan costs free and includes the AGPL-3.0 open-source software. It is the right choice for individual developers, teams comfortable operating a self-hosted command-line tool, and organizations that can work within the license.

Commercial users can buy Priority support, billed as a year's worth of entitlement, for direct email support from the developer. The price is custom pricing. This add-on is relevant when response access matters in production; it does not change the software's free licensing model.

Platforms

dcd runs on Linux and macOS. Go 1.19 or newer users can install it with go install github.com/boyter/dcd@latest. Release 1.1.0 removed Windows support for full filesystem compatibility, so Windows users must use WSL. That makes dcd a stronger fit for Unix-based development environments than for teams expecting a native Windows executable.

Who it's for

Choose dcd for repository maintainers, refactoring efforts, and CI checks where adjustable near-duplicate matching is more useful than a binary exact-copy report. Its JSON, HTML, and PBM outputs suit teams that need both machine-readable gates and human review. It is less suitable for users who require native Windows operation or editor-integrated feedback.

Pros and cons

• Pros: Matching controls cover fuzzy similarity, gaps, and modified-line holes, so scans can reflect the way duplicated code evolves.
• Pros: JSON output and CI integration support repeatable automated checks.
• Pros: Interactive HTML heatmaps and scatter plots make duplication patterns easier to investigate.
• Pros: Parsing through scc covers more than 250 languages, and .ignore support helps keep intentional or generated repetition out of results.
• Cons: Windows users need WSL because native support was removed in release 1.1.0.
• Cons: There is no IDE integration, so findings remain outside the editor workflow.
• Cons: The AGPL-3.0 license and command-line, self-hosted model may require more operational and licensing consideration than a hosted commercial service.

Alternatives

Duplo is a free Linux, macOS, and Windows option with prebuilt binaries for Alpine Linux, macOS, and Windows, making it preferable when native Windows distribution matters.

PMD is a free, BSD-style-licensed static code analyzer for Linux, macOS, self-hosted deployments, and Windows; choose it when a broader static-analysis tool is the priority.

Simian Similarity Analyzer is free, open source, Apache-licensed software for Linux, macOS, and Windows, suitable when that license and platform mix fit better.

CloneWorks is free on Linux, macOS, and Windows, with acknowledgement and free-redistribution requirements.

jscpd is a free option spanning API, Linux, macOS, self-hosted, and Windows environments.

NiCad is free, MIT-licensed software for Linux, macOS, self-hosted, and Windows, but requires OpenTxl 11 or later.

CCFinderSW is a free, MIT-licensed Windows-only tool requiring Java Runtime Environment 8 or later.

Algo VPN is a free, self-hosted VPN setup project rather than a duplicate-code detector, so it is not a direct substitute for dcd.

For a broader category comparison, see the Code Clone Detection Tools list.

Verdict

dcd is a strong choice for Linux and macOS developers who want configurable duplicate detection, broad language coverage, visual reports, and JSON suitable for CI. Choose it when repository-level, self-hosted analysis matters most. Look elsewhere if native Windows support or IDE integration is essential.