CodeSniff | Hybrid Code Plagiarism Detector
A high-accuracy hybrid code plagiarism detector that combines K-gram Winnowing, weighted Jaccard, LCS, and JavaParser-based AST similarity to instantly detect Type 1-3 code clones.

Live Demo · Report Bug · Request Feature

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About

"In a world where code is copied, CodeSniff sees what eyes can't."

CodeSniff is a token-based code similarity analyzer designed to detect plagiarism in Java source files. It uses the K-gram fingerprinting technique combined with the Winnowing algorithm the same approach used by Stanford's MOSS system to identify copied code even when variable names are changed, comments are removed, or statements are reordered.

Currently supporting Java with plans to expand to Python, C++, JavaScript and more in future releases through AI-powered semantic analysis.

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🚀 Features

⚠️ Current Version (v2.0): Supports Java source files only. Multi-language support planned for future releases.

• 🔍 Token-based similarity detection using K-gram algorithm
• 🪟 Winnowing algorithm for efficient fingerprint selection
• 🌳 AST Structural Comparison via compiler-level parsing (JavaParser)
• 📜 LCS Statement Alignment for flow-level similarity checks
• ☕ Java source file upload and pairwise comparison
• 💻 Direct code paste for quick Java code analysis
• 📊 Similarity percentage results table and detailed visual report
• ⚙️ Configurable options — K-gram size, window size, ignore comments
• ☁️ Cloud Persistence & History tracking for authenticated users
• 🌐 Fully deployed on cloud infrastructure

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🛠️ Tech Stack

Frontend

Technology	Purpose
HTML5 / CSS3	UI structure and styling
Vanilla JavaScript	SPA routing and API calls
Vercel	Hosting and deployment

Backend

Technology	Purpose
Java 17	Core language
Spring Boot 3.3.5	REST API framework
Maven	Build and dependency management
Azure App Service F1	Cloud hosting (24/7)

Database & Infrastructure

Technology	Purpose
In-Memory Cache	Temporary report storage
GitHub Actions	CI/CD pipeline
Nginx	Reverse proxy

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🏗️ System Architecture

User Browser
     │
     ▼
┌─────────────────┐
│  Vercel          │  codesniff.tech
│  (Frontend)      │  HTML + CSS + JS
└────────┬────────┘
         │ API calls
         ▼
┌─────────────────────────┐
│  Azure App Service F1    │  codesniff-backend.azurewebsites.net
│  Spring Boot Backend     │
│  ┌─────────────────┐    │
│  │AnalyzeController│    │
│  └────────┬────────┘    │
│           │              │
│  ┌────────▼────────┐    │
│  │SimilarityEngine  │    │
│  └────────┬────────┘    │
│           │              │
│  ┌────────▼────────┐    │
│  │Tokenizer         │    │
│  └────────┬────────┘    │
│           │              │
│  ┌────────▼────────┐    │
│  │CodeNormalizer    │    │
│  └─────────────────┘    │
└─────────────────────────┘

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🔬 Detection Pipeline

                            Source Code A / B
                             ┌───────┴───────┐
                             ▼               ▼
                        [Raw Code]      [Tokenizer]
                             │               │
                             │               ├──────────────────────┐
                             ▼               ▼                      ▼
                        [ASTBuilder]   [CodeNormalizer]     [StatementGrouper]
                             │               │                      │
                             ▼               ▼                      ▼
                       [ASTComparator]  [Winnowing]            [LcsEngine]
                             │               │                      │
                             ▼               ▼                      ▼
                         AST Score      Jaccard & Coverage      LCS Score
                             │               │                      │
                             └───────────────┼──────────────────────┘
                                             ▼
                                      [Hybrid Score]

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📦 Clone Types Detected

Clone Type	Description	Detected
Type 1	Exact copy	✅
Type 2	Renamed identifiers	✅
Type 3	Added/removed statements	✅
Type 4	Semantic similarity	⚠️ Partial

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🚀 Getting Started

Prerequisites

• Java 17+
• Maven 3.9+

Installation

# Clone the repository
git clone https://github.com/Kunal-htr/codesniff.git

# Navigate to project
cd codesniff

# Install dependencies
mvn clean install

Configuration

Create src/main/resources/application.properties:

server.port=9090

Run Locally

mvn spring-boot:run

Open http://localhost:9090 in your browser.

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🔌 API Reference

Analyze Code Similarity (JSON)

POST /api/analyze
Content-Type: application/json

Request Body:

{
  "submissions": [
    { "name": "A.java", "content": "public class A { int sum(int[] a){int s=0;for(int i=0;i<a.length;i++){s+=a[i];}return s;} }" },
    { "name": "B.java", "content": "public class B { int total(int[] d){int t=0;for(int j=0;j<d.length;j++){t+=d[j];}return t;} }" }
  ],
  "options": {
    "omitComments": true,
    "k": 6,
    "window": 4
  }
}

Response:

{
  "summary": [
    {
      "a": "A.java",
      "b": "B.java",
      "score": 1.0,
      "jaccard": 1.0,
      "coverage": 1.0,
      "reportId": "d741ca12-a16f-40c2-9ee6-4e59f427ee0e"
    }
  ]
}

Get Detailed Pairwise Report

GET /api/report/{id}

Response:

{
  "nameA": "A.java",
  "nameB": "B.java",
  "jaccard": 1.0,
  "coverage": 1.0,
  "lcs": 1.0,
  "ast": 1.0,
  "hybrid": 1.0,
  "verdict": "High",
  "verdictDescription": "High similarity detected. There is a high probability of direct copy/paste or minimal rewriting.",
  "operatorDivergent": false,
  "metadata": {
    "k": 6,
    "window": 4,
    "omitComments": true,
    "fingerprintMatchCount": 15,
    "fingerprintCountA": 15,
    "fingerprintCountB": 15
  }
}

Health Check

GET /api/health

CodeSniff is alive!

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🛡️ Input Validation & Error Handling

CodeSniff v2.0 introduces strict input validation and centralized exception handling. Requests are validated using Jakarta Bean Validation before reaching the analysis engine.

Constraints:

• submissions: Must have between 1 and 200 files per batch.
• name & content: Must not be blank.
• k: Must be between 3 and 64.
• window: Must be between 1 and 128.

Error Response Format (ApiErrorDTO):

When a validation constraint is violated, or a report ID is not found, the API returns a structured error object instead of raw stack traces:

{
  "error": "Bad Request",
  "message": "Validation failed: submissions[0].content: Submission content must not be blank",
  "status": 400,
  "timestamp": 1784260000000
}

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📁 Project Structure

codesniff/
├── src/
│   └── main/
│       ├── java/
│       │   └── backend/
│       │       ├── App.java                 # Spring Boot entry point
│       │       ├── common/                  # Global exceptions, DTOs & utilities
│       │       ├── config/                  # Security, CORS & Rate Limiting configs
│       │       └── modules/                 # Domain-driven architecture modules
│       │           ├── report/              # Batch generation, PDF/CSV exports
│       │           ├── similarity/          # Core AST matching & Winnowing engine
│       │           └── user/                # Authentication, JWT & Profile management
│       └── resources/
│           ├── db/migration/                # Flyway SQL migrations
│           └── application.properties       # Spring Boot config
├── frontend/                                # Frontend UI (Vercel deployment)
│   ├── index.html                           # Main UI
│   ├── app.js                               # Frontend logic & routing
│   └── style.css                            # Styling
├── test_samples/                            # Standard plagiarism test samples
├── Dockerfile                               # Container config
└── pom.xml                                  # Maven config

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🔄 CI/CD Pipeline

git push to main
      │
      ▼
GitHub Actions triggers
      │
      ▼
Maven build + test
      │
      ▼
Deploy to Azure App Service
      │
      ▼
Live in ~50 seconds ✅

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📊 Performance

Metric	Value
Average response time	~200ms
Max file size	1MB
Supported languages	All text-based
Concurrent comparisons	Multiple pairs

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📦 Modules

Module	Name	Status	Version
Module 1	Similarity Engine	✅ Complete	v0.5
Module 2	Report & Visualization	✅ Complete	v1.0
Module 3	Authentication and Security	✅ Complete	v1.5
Module 4	Database & Storage Integration	✅ Complete	v2.0
Module 5	Future AI Integration	🔄 Planned	v2.5

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📄 License

This project is licensed under the MIT License.

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🙏 Acknowledgements

• Spring Boot
• Vercel
• Azure
• Winnowing Algorithm — Schleimer, Wilkerson, Aiken (2003)

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