InterviewLab

Problem: Traditional technical interview practice often lacks realism, immediate feedback, and interactive voice-based engagement.

Solution: InterviewLab delivers AI-driven technical interviews using real-time voice conversations, live code execution, and in-depth feedback, powered by LangGraph and LiveKit.

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Python 3.11+ TypeScript 5.0+ LangGraph 0.0.40+ LiveKit 0.11.0+ OpenAI 1.0.0+ License GNU Status Portfolio-Project

Portfolio Project — Production-ready codebase demonstrating AI system architecture.

Aim

Provide candidates with realistic interview practice through:

• Natural voice conversations with AI interviewer
• Live code execution in isolated sandbox
• Comprehensive feedback on communication, technical knowledge, problem-solving, and code quality
• Resume-based questions tailored to candidate background

High-Level Architecture

graph TB
    subgraph Frontend
        FE[Next.js React App]
    end

    subgraph Backend
        API[FastAPI Server]
        ORCH[LangGraph Orchestrator]
    end

    subgraph Voice
        LK[LiveKit Server]
        AGENT[LiveKit Agent]
        TTS[OpenAI TTS]
        STT[OpenAI STT]
    end

    subgraph Services
        SB[Docker Sandbox]
        LLM[GPT-4o-mini]
        DB[PostgreSQL]
        REDIS[Redis Cache]
    end

    FE -->|HTTP REST| API
    FE -->|WebSocket| LK
    API -->|HTTP| LK
    API -->|SQL| DB
    API -->|Cache| REDIS
    LK -->|WebSocket| AGENT
    AGENT -->|LangGraph| ORCH
    ORCH -->|API| LLM
    ORCH -->|Docker| SB
    AGENT -->|API| TTS
    AGENT -->|API| STT

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Core Components

Component	Technology	Purpose
Orchestrator	LangGraph	State machine managing interview flow
Agent	LiveKit Agents	Real-time voice agent (STT/TTS)
LLM	GPT-4o-mini	Question generation, decision making
Sandbox	Docker	Isolated code execution
Database	PostgreSQL	Interview state, checkpoints
Cache	Redis	State caching, session management

How It Works

Interview Flow

sequenceDiagram
    participant U as User
    participant F as Frontend
    participant A as API
    participant LK as LiveKit
    participant AG as Agent
    participant O as Orchestrator
    participant LLM as GPT-4o-mini

    U->>F: Start Interview
    F->>A: POST interviews
    A->>LK: Create Room
    F->>LK: Connect WebSocket
    LK->>AG: Bootstrap Agent
    AG->>O: Initialize
    O->>LLM: Generate Greeting
    LLM->>O: Response
    O->>AG: next_message
    AG->>LK: TTS Audio
    LK->>U: Hear Greeting

    loop Conversation
        U->>LK: Speak
        LK->>AG: STT Text
        AG->>O: execute_step
        O->>LLM: Detect Intent
        O->>LLM: Decide Next Action
        O->>LLM: Generate Response
        O->>AG: Response
        AG->>U: TTS Audio
    end

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State Management

• LangGraph MemorySaver: In-memory state per interview (thread_id)
• Database Checkpoints: Persistent state after each turn
• Reducers: Append-only fields (conversation_history, questions_asked)
• Single Writer: Critical fields (next_message, phase) written by one node

Current Performance

Strengths

• ✅ Real-time voice with <3s latency
• ✅ State persistence via checkpoints
• ✅ Concurrent interviews (isolated by thread_id)
• ✅ Code execution in isolated Docker containers
• ✅ Comprehensive feedback with skill breakdowns

Project Structure

InterviewLab/
├── src/                    # Backend (Python/FastAPI)
│   ├── agents/            # LiveKit agent logic
│   ├── api/               # REST API implementation
│   │   └── v1/
│   │       └── endpoints/ # Endpoints for interviews, resumes, voice, sandbox
│   ├── core/              # Configuration, database, and authentication utilities
│   ├── models/            # Database models for core entities
│   ├── schemas/           # Pydantic schemas for data validation
│   └── services/          # Business logic and subsystems
│       ├── analysis/      # Interview response and code analysis
│       ├── analytics/     # Analytics functionality
│       ├── data/          # Checkpointing and state management
│       ├── execution/     # Secure code sandboxing
│       ├── logging/       # Interview activity logging
│       ├── orchestrator/  # State orchestration using LangGraph
│       └── voice/         # LiveKit voice management
├── frontend/              # Frontend (Next.js + React)
│   ├── app/              # App routing and authentication
│   ├── components/       # UI components (interview, analytics, UI kit)
│   ├── lib/              # API client and store utilities
│   └── hooks/            # Custom React hooks
├── docs/                  # Documentation and guides
├── alembic/               # Database migration scripts
├── docker-compose.yml     # Local dev orchestration
├── Dockerfile             # Production build configuration
└── pyproject.toml         # Backend dependencies and settings

Documentation

• Architecture - System architecture and component relationships
• API Reference - REST API endpoints
• Frontend - Next.js frontend architecture and development
• Voice Infrastructure - LiveKit setup and agent architecture
• User Guide - How to use InterviewLab
• Local Development - Setup and development workflow
• LangGraph Guide - State, nodes, and orchestration
• Deployment - Railway and Vercel deployment

Quick Start

# Backend
cd src
uvicorn main:app --reload

# Frontend
cd frontend
npm install
npm run dev

# Agent (requires LiveKit server)
python -m src.agents.interview_agent

See Local Development for detailed setup.

Tech Stack

Backend

• FastAPI - Modern async web framework
• Python 3.11+ - Programming language
• LangGraph 0.0.40+ - State machine orchestration
• SQLAlchemy 2.0+ - ORM with async support
• Alembic - Database migrations
• LiveKit Agents - Real-time voice agents
• OpenAI GPT-4o-mini - LLM for question generation
• Instructor - Structured LLM outputs
• PostgreSQL - Primary database
• Redis - Caching and state management
• Docker - Code sandbox execution

Frontend

• Next.js 16.1 - React framework
• TypeScript 5.0+ - Type safety
• React 19.2 - UI library
• Tailwind CSS 4 - Styling
• Zustand - State management
• TanStack Query - Data fetching
• Monaco Editor - Code editor
• Framer Motion - Animations
• LiveKit Client - WebRTC integration

Deployment

• Railway - Backend and agent hosting
• Vercel - Frontend hosting

License

GNU General Public License v3.0