jscpd

name	jscpd
description	Copy-paste detector for 220+ languages. Detect duplicated code and measure duplication percentages.

jscpd

Copy-paste detector for programming source code, supports 150+ languages. Use this skill to run jscpd and understand its output.

Quick Start

# Run with ai reporter (compact output optimized for agents)
npx jscpd --reporters ai <path>

# With ignore patterns
npx jscpd --reporters ai --ignore "**/node_modules/**,**/dist/**" <path>

# Scope to specific formats
npx jscpd --reporters ai --format "javascript,typescript" <path>

AI Reporter Output Format

The ai reporter produces compact, token-efficient output designed for agent consumption:

Clones:
src/ foo.ts:10-25 ~ bar.ts:42-57
src/utils/helpers.ts:100-120 ~ src/utils/other.ts:5-25
---
3 clones · 4.2% duplication

Each line represents one clone pair:

• Same file: path/file.ts 10-25 ~ 45-60 (shared path shown once)
• Same directory: shared/prefix/ file-a.ts:10-25 ~ file-b.ts:42-57 (common prefix factored out)
• Different paths: path/a.ts:10-25 ~ path/b.ts:42-57

Options

Option	Description
--reporters ai	Use the AI-optimized reporter (compact clone list for agents)
--reporters html	Generate HTML report
--reporters json	Output JSON report
--min-tokens N	Minimum tokens to consider a duplication (default: 50)
--min-lines N	Minimum lines to consider a duplication (default: 5)
--min-similarity N	Minimum similarity percentage (default: 100, range: 1-100)
--threshold N	Exit with error if duplication % exceeds N
--ignore "glob"	Ignore patterns (comma-separated)
--format "list"	Limit to specific languages (e.g. typescript,javascript)
--cross-formats "groups"	Detect clones across related formats (e.g. javascript,typescript or the js-ts preset)
--pattern "glob"	Glob pattern to select files
--gitignore	Respect .gitignore
--output "path"	Directory to write reports to
--silent	Suppress output (useful with --output only)
--list-output	Print clone list to stdout (alternative to ai reporter)
--store-path "path"	Directory for LevelDB cache
--no-tips	Disable tips in output (enabled by default in CI)
--config "path"	Path to .jscpd.json config file

Cross-Format Clone Detection

By default each format is compared only against itself. --cross-formats defines groups of related formats that share one comparison pool, so a block duplicated between a .js and a .ts file is reported as a clone:

# One group: compare JavaScript and TypeScript files together
npx jscpd --reporters ai --cross-formats "javascript,typescript" <path>

# Preset covering javascript, jsx, typescript, tsx
npx jscpd --reporters ai --cross-formats "js-ts" <path>

# Multiple groups are separated by ";"
npx jscpd --reporters ai --cross-formats "javascript,typescript;css,scss" <path>

Notes:

• When a group mixes TypeScript with JavaScript, TS files are compared with erasable type syntax stripped, so function f(a: number): void matches function f(a). Reported positions still reference the original source.
• Groups need at least two formats; groups sharing a format are merged into one pool.
• In per-format statistics, a cross-format clone is attributed to one member format of the group.
• In config files the key is crossFormats (or cross-formats) and accepts a string ("javascript,typescript;css,scss"), an array of strings (["javascript,typescript", "css,scss"]), or an array of arrays ([["javascript","typescript"],["css","scss"]]).

Configuration File

Create a .jscpd.json in your project root:

{
  "threshold": 0,
  "reporters": ["ai"],
  "ignore": ["**/node_modules/**", "**/dist/**", "**/*.min.*"],
  "format": ["typescript", "javascript"],
  "minLines": 5,
  "minTokens": 50,
  "output": "./reports/jscpd"
}

Refactoring Duplicated Code

Once you've detected clones, use the dry-refactoring skill for a guided workflow to eliminate them:

→ dry-refactoring — step-by-step refactoring strategies and workflow for removing duplication. Install with:

npx skills add https://github.com/kucherenko/jscpd --skill dry-refactoring