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jscpd
Copy-paste detector for programming source code, supports 220+ 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% duplicationEach 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) |
--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) |
--summary | Append a codebase summary: top files/folders by tokens, lines, size, complexity, with duplication share |
--summary-top N | Number of entries in each summary top list (default: 10) |
--summary-by metric | Summary ranking metric: tokens, lines, size, complexity (default: tokens) |
--pattern "glob" | Glob pattern to select files |
--no-gitignore | Do not respect .gitignore (it is respected by default) |
--output "path" | Directory to write reports to |
--silent | Suppress console output (useful with file reporters and --output) |
--list | List all supported formats and exit |
--no-tips | Disable tips in output (enabled by default in CI) |
--config "path" | Path to .jscpd.json config file |
Codebase Summary (--summary)
--summary appends a refactoring-hotspot overview to the run output — use it to decide where to refactor first before diving into individual clones:
# Compact clone list + compact summary, optimized for agents
npx jscpd --reporters ai --summary --no-tips <path>
# Rank by complexity instead of tokens, top 5 lists
npx jscpd --reporters ai --summary --summary-by complexity --summary-top 5 <path>With the ai reporter the summary is one line per entry:
Summary by tokens (321 files, 129 folders):
files (tokens/lines/size/cx/dup%):
src/files.ts 2052/363/11662/80/0.0%
...
folders (files/tokens/lines/size):
src/core 8/5264/843/27136
...How to read it:
- Top files are ranked by the
--summary-bymetric, but every row carries all metrics —tokens/lines/size/cx/dup%. - cx is a language-agnostic cyclomatic-complexity estimate from the token stream (1 + decision-point tokens like
if/while/&&); treat it as a ranking signal, not an exact metric. - dup% is the share of the file's lines covered by detected clones — a large file with high
dup%is the best refactoring target. - Folders aggregate files into their direct parent directory (no cumulative ancestor totals).
- In
consolereporters the summary renders as aligned tables; in thejsonreport it appears as an additivesummarykey (absent when the flag is off).
Config file equivalents: "summary": true, "summaryTop": 10, "summaryBy": "tokens".
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): voidmatchesfunction 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(orcross-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