check-similarity

Category: Development & Coding | Uploader: yutakobayashidev | Downloads: 0 | Version: v1.0（Latest）

Detects duplicate TypeScript/JavaScript code using AST comparison for refactoring. Use when the user wants to find similar or duplicated functions, plan refactoring, or clean up redundant code in TS/JS projects.

Changelog: Source: GitHub https://github.com/yutakobayashidev/dotnix

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SKILL.md

---
name: check-similarity
description: Detects duplicate TypeScript/JavaScript code using AST comparison for refactoring. Use when the user wants to find similar or duplicated functions, plan refactoring, or clean up redundant code in TS/JS projects.
user-invocable: true
---

# similarity-ts: AI Assistant Guide

## Purpose

Detects duplicate TypeScript/JavaScript code using AST comparison for refactoring.

## AI用プロンプト / AI Prompt

日本語:

```
`similarity-ts .` でコードの意味的な類似が得られます。あなたはこれを実行し、ソースコードの重複を検知して、リファクタリング計画を立てます。細かいオプションは similarity-ts -h で確認してください。
```

English:

```
Run `similarity-ts .` to detect semantic code similarities. Execute this command, analyze the duplicate code patterns, and create a refactoring plan. Check `similarity-ts -h` for detailed options.
```

## Installation

```bash
cargo install similarity-ts
# check options
similarity-ts --help
```

## Key Options

- `--threshold <0-1>`: Similarity threshold (default: 0.8)
- `--min-tokens <n>`: Skip functions with <n AST nodes (recommended: 20-30)
- `--print`: Show actual code snippets
- `--experimental-types`: Enable type similarity detection (interfaces, type aliases)
- `--filter-function <name>`: Filter results by function name (substring match)
- `--filter-function-body <text>`: Filter results by function body content (substring match)

## AI Refactoring Workflow

### 1. Broad Scan

Find all duplicates in codebase:

```bash
similarity-ts src/ --threshold 0.85 --min-tokens 25
```

### 2. Focused Analysis

Examine specific file pairs:

```bash
similarity-ts file1.ts file2.ts --threshold 0.8 --min-tokens 20 --print
```

### 3. Threshold Tuning

If no results, progressively lower:

```bash
similarity-ts file1.ts file2.ts --threshold 0.75 --min-tokens 20
similarity-ts file1.ts file2.ts --threshold 0.7 --min-tokens 20
```

## Output Format

```
Function: functionName (file.ts:startLine-endLine)
Similar to: otherFunction (other.ts:startLine-endLine)
Similarity: 85%
```

## Effective Thresholds

- `0.95+`: Nearly identical (variable renames only)
- `0.85-0.95`: Same algorithm, minor differences
- `0.75-0.85`: Similar structure, different details
- `0.7-0.75`: Related logic, worth investigating

## Refactoring Strategy

1. **Start with high threshold** (0.9) to find obvious duplicates
2. **Compare specific pairs** when similarity found
3. **Use --print** to see actual code differences
4. **Extract common logic** into shared functions/modules
5. **Re-run after refactoring** to verify no new duplicates

## Common Patterns to Refactor

- **Data processing loops** with different field names
- **API handlers** with similar request/response logic
- **Validation functions** with different rules
- **State management** with repeated patterns

## Best Practices

- Use `--min-tokens` for accurate complexity filtering (20-30 tokens)
- Focus on files with 80%+ similarity first
- Check if similar functions are in same module (easier to refactor)
- Consider function size - larger duplicates have more impact
- Look for patterns across multiple files, not just pairs

## Test Scenario: Following README Examples

Test the tool's functionality by running through README examples:

```bash
# 1. Quick Start - Zero configuration
similarity-ts

# 2. Analyze specific paths
similarity-ts src/ lib/

# 3. Custom threshold
similarity-ts . --threshold 0.9

# 4. Print code details
similarity-ts . --print

# 5. Type checking (experimental)
similarity-ts . --experimental-types

# 6. Specific file extensions
similarity-ts ./src --extensions ts,tsx

# 7. Examples directory test
similarity-ts examples/specs/duplicate-functions.ts --threshold 0.8 --min-tokens 20
similarity-ts examples/specs/duplicate-types.ts --experimental-types --threshold 0.8
```

### Expected Results

1. **Function Detection** (duplicate-functions.ts):
   - calculateUserAge vs calculateCustomerAge (~95%)
   - findMaxValue vs getMaximumValue (~85%)
   - processUserData vs processCustomerData (~90%)

2. **Type Detection** (duplicate-types.ts):
   - User vs Customer (100%)
   - UserResponse vs CustomerResponse (~85%)
   - ApiResponse vs ServiceResponse (100%)

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