jscpd

Copy/paste detector for programming source code. 220+ formats, Rust engine, self-contained binary, AI-ready with MCP server and token-efficient reporter.

Documentation: https://jscpd.dev

jscpd implements the Rabin-Karp algorithm to find duplicated code blocks across files.

Quick Start

# macOS / Linux
curl -fsSL https://jscpd.dev/install.sh | bash

# Windows (PowerShell)
irm https://jscpd.dev/install.ps1 | iex

# No install — run once with npx (Node.js)
npx jscpd .

Then scan a project:

jscpd /path/to/code

Other install methods

GitHub Action

- uses: kucherenko/jscpd@v5
  with:
    threshold: 5

Uploads SARIF results to GitHub Code Scanning by default. See CI & Pre-Commit Hooks for all inputs and outputs.

Related MCP server: tree-sitter-analyzer

Documentation

Features

jscpd v5 is a Rust engine that ships as a self-contained binary — no runtime required — under two npm names (jscpd installs the jscpd command, cpd installs cpd), on crates.io, Homebrew, Nix, Docker, and as a GitHub Action.

• 224 language formats with cross-format detection (Vue SFC, Svelte, Astro, Markdown) and --cross-formats groups to match clones across JavaScript and TypeScript

• Prebuilt for 8 platforms — macOS arm64/x64, Linux arm64/x64 (glibc and musl), Windows arm64/x64

• 15 reporters: console, console-full, json, xml, csv, html, markdown, badge, sarif, codeclimate, openmetrics, ai, xcode, threshold, silent

• Clone baseline — gate CI on new duplication only. --baseline .jscpd-baseline.json with --fail-on-new-clones[=N] tolerates legacy clones and fails the build on regressions; --baseline-from-ref origin/main does the same without a committed file (see docs)

• GitLab-ready reporters — codeclimate (gl-code-quality-report.json) and openmetrics (jscpd-metrics.txt) plug into artifacts:reports

• Git blame with side-by-side author comparison (--blame --reporters console-full)

• --summary — codebase summary: top files and folders by tokens, lines, size, and a complexity estimate — refactoring hotspots straight from the scan (see docs)

• --mcp — built-in MCP server over stdio: point your AI assistant at the binary and it can check snippets for duplication against your codebase (see docs)

• AI reporter — token-efficient output for LLM pipelines (~79% fewer tokens than console)

• --skip-isolated — ignore duplication between monorepo folders owned by different teams

• --workers — control parallelism for file tokenization and detection (default: all CPU cores)

• Config discovery — .jscpd.json, .config/jscpd.json, or the jscpd key in package.json

See the Rust docs for the full CLI reference and rust/CHANGELOG.md for release notes.

Looking for v4?

jscpd v4 (TypeScript engine, Node.js API, LevelDB/Redis stores) is maintained on the master-v4 branch and published as jscpd@4 / the latest-4 dist-tag. README-v4.md describes it in one page (install, CLI, API, packages, maintenance policy); the same content is at https://jscpd.dev/getting-started/v4.

Packages

Who Uses jscpd

The jscpd npm package is downloaded 10M+ times per month, and ~5,000 repositories declare it on GitHub's dependents graph.

Bundled by analysis platforms:

• GitHub Super Linter — official GitHub linter aggregator, bundles jscpd as its copy/paste detector and runs it by default; 15,500+ workflow files on GitHub reference Super Linter (as of Sep 2026)

• MegaLinter — open-source linter aggregator for CI, ships jscpd in every flavor including ci_light

• Codacy — automated code analysis platform, jscpd powers the duplication engine

Explicitly enabled in Super Linter (VALIDATE_JSCPD: true) by dozens of public repositories, including:

• A2A — Google's Agent2Agent protocol (25k+ stars)

• RimSort — mod manager for RimWorld (1.2k+ stars); also runs jscpd directly with its own .jscpd.json

• Contact Center AI samples — official Google Cloud samples, with a dedicated jscpd config

• Drifty — open-source download manager

Used in notable projects:

• OpenClaw — personal AI assistant, runs jscpd as a duplication gate in its check scripts

• DeepSeek Harness — DeepSeek's plugin harness, jscpd config in CI

• degit — Rich Harris's project scaffolder

• MEGA webclient — the MEGA.nz web client

• Microsoft TypeAgent

• Salesforce DX VS Code

• Alibaba AppWorks — embeds jscpd as a library

• OVHcloud manager — OVHcloud's customer control panel

• KiroCrew — self-improving persistent development workspace

Benchmark

Compared against other copy/paste detectors on the fixtures/ corpus (547 files, 150+ formats), default thresholds, wall-clock time on Apple Silicon:

Methodology, cross-format detection and AI-token-efficiency comparisons: benchmark/BENCHMARK.md. Re-run with benchmark/benchmark.sh.

AI-Ready Features

jscpd integrates into AI-powered workflows through three mechanisms:

AI Reporter

Token-efficient output for LLM pipelines (~79% fewer tokens than the default console reporter):

jscpd --reporters ai /path/to/source              # compact clone list
jscpd --reporters ai --summary /path/to/source    # + compact codebase summary

Agent Skills

Two installable skills that teach AI coding assistants how to use jscpd and refactor detected duplications:

After installation, ask your agent to "find and fix code duplication" and it will invoke jscpd with the right options and act on the results.

MCP Server

jscpd --mcp /path/to/project scans once and serves the Model Context Protocol over stdio, so an assistant can check any snippet for duplication against the codebase on demand.

See AI-Ready docs for full details.

Contributing

See CONTRIBUTING.md for the development setup, test policy, and pull request requirements. In short:

cd rust
cargo nextest run --workspace
cargo clippy --workspace --all-targets -- -D warnings
cargo fmt --all --check

Security issues go through the security policy, not public issues.

Backers

Thank you to all our backers! 🙏 [Become a backer]

Sponsors

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License

MIT © Andrey Kucherenko