check-similarity

name	check-similarity
description	Detect duplicate code using AST-based similarity analysis. Auto-selects the right tool based on file types in the project (similarity-ts for TypeScript/JavaScript, similarity-py for Python, similarity-mbt for MoonBit, similarity-rs for Rust, etc).
argument-hint	[path] [--threshold 0.85] [--print]
allowed-tools	Bash(similarity-* *) Bash(cargo run -p similarity-* *) Read Grep Glob

Code Similarity Detection (Multi-Language)

What to do

Detect which languages are present in the target path and run the appropriate similarity tool. Then analyze results and propose refactoring.

Step 1: Detect language and select tool

Check the target path for file extensions:

Extension	Tool
.ts, .tsx, .js, .jsx	similarity-ts
.py	similarity-py
.mbt	similarity-mbt
.rs	similarity-rs
.php	similarity-php
.ex, .exs	similarity-elixir
.css, .scss	similarity-css

Before running, check if the command exists. If not, install it:

which similarity-<lang> || cargo install similarity-<lang>

Step 2: Run analysis

similarity-<lang> $ARGUMENTS

If no arguments given:

similarity-<lang> . --threshold 0.85 --min-lines 5

For TypeScript, also consider type similarity:

similarity-ts . --threshold 0.85 --min-tokens 25 --experimental-types

Step 3: Analyze and report

Categorize results by priority:

1. 100% similarity: Exact duplicates - must refactor
2. 95-100%: Near-identical - high-value refactoring targets
3. 85-95%: Same pattern - consider extracting shared logic
4. < 85%: Similar structure - investigate if related

Report the findings grouped by file, sorted by similarity (highest first). For each high-priority pair, propose a concrete refactoring with before/after code.

Common Options (all tools)

Option	Description
--threshold <0-1>	Similarity threshold (default: 0.85)
--min-lines <n>	Skip short functions (default: 3)
--print	Show code snippets
--fail-on-duplicates	Exit code 1 if duplicates found
--filter-function <name>	Filter by function name

CI Integration

# Fail CI if near-exact duplicates exist
similarity-<lang> . --threshold 0.95 --min-lines 5 --fail-on-duplicates