| 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:
- 100% similarity: Exact duplicates - must refactor
- 95-100%: Near-identical - high-value refactoring targets
- 85-95%: Same pattern - consider extracting shared logic
- < 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
similarity-<lang> . --threshold 0.95 --min-lines 5 --fail-on-duplicates
