diff --git a/devdocs/v1/IMPLEMENTATION_PLAN.md b/devdocs/v1/IMPLEMENTATION_PLAN.md
index e96c913..7d8e932 100644
--- a/devdocs/v1/IMPLEMENTATION_PLAN.md
+++ b/devdocs/v1/IMPLEMENTATION_PLAN.md
@@ -6,11 +6,12 @@
 GoalsBreakDown/
 ├── app.py                      # Flask application entry point
 ├── config.py                   # Configuration constants
-├── database.py                 # TinyDB initialization and operations
+├── database.py                 # SQLite database operations
 ├── auth.py                     # Authentication helpers
-├── requirements.txt            # Python dependencies
-├── data/                       # TinyDB data directory
-│   └── db.json                 # TinyDB database file
+├── schema.py                   # SQLite table creation & migration
+├── pyproject.toml              # Python dependencies (uv-managed)
+├── data/                       # SQLite data directory
+│   └── db.sqlite               # SQLite database file
 ├── static/
 │   ├── css/
 │   │   ├── style.css           # Global styles
@@ -20,14 +21,14 @@ GoalsBreakDown/
 │       ├── api.js              # API client utilities
 │       ├── auth.js             # Authentication logic
 │       ├── goals.js            # Goal page logic
-│       ├── tasks.js            # Task page logic
-│       └── sortable.min.js     # Drag-and-drop library
+│       └── tasks.js            # Task page logic
 └── templates/
     ├── base.html               # Base template with navigation
     ├── login.html              # Login page
     ├── register.html           # Registration page
     ├── goals.html              # Goal CRUD page
-    └── tasks.html              # Task CRUD page with scroll view
+    ├── tasks.html              # Task CRUD page with scroll view
+    └── admin.html              # Admin user management page
 ```
 
 ## 2. Dependencies & Environment Management
@@ -38,80 +39,69 @@ GoalsBreakDown/
 uv init --no-readme
 
 # Add dependencies
-uv add flask tinydb bcrypt
+uv add flask bcrypt
 
 # Run the application
-uv run python app.py
+uv run flask run
 ```
 
-### 2.2 requirements.txt (managed by uv)
-```
-flask==3.0.0
-tinydb==4.8.0
-bcrypt==4.1.2
-```
-
-### 2.3 pyproject.toml (auto-generated by uv)
+### 2.2 pyproject.toml (managed by uv)
 ```toml
 [project]
 name = "goalsbreakdown"
 version = "0.1.0"
-requires-python = ">=3.10"
+requires-python = ">=3.13"
 dependencies = [
-    "flask>=3.0.0",
-    "tinydb>=4.8.0",
-    "bcrypt>=4.1.2",
+    "flask>=3.1.3",
+    "bcrypt>=5.0.0",
 ]
 ```
 
-## 3. Database Schema (TinyDB)
+## 3. Database Schema (SQLite)
 
-### 3.1 Collections (TinyDB Tables)
+### 3.1 Tables
 
 **users** table:
-```json
-{
-  "user_id": 1,
-  "username": "admin",
-  "password_hash": "$2b$12$...",
-  "role": "admin",
-  "max_goals": 10
-}
+```sql
+CREATE TABLE users (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    username TEXT NOT NULL UNIQUE,
+    password_hash TEXT NOT NULL,
+    role TEXT NOT NULL DEFAULT 'user',
+    max_goals INTEGER NOT NULL DEFAULT 5
+);
 ```
 
 **goals** table:
-```json
-{
-  "goal_id": 1,
-  "user_id": 1,
-  "title": "Learn Python",
-  "activated": true
-}
+```sql
+CREATE TABLE goals (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id INTEGER NOT NULL,
+    title TEXT NOT NULL,
+    activated INTEGER NOT NULL DEFAULT 1,
+    FOREIGN KEY (user_id) REFERENCES users(id)
+);
 ```
 
 **tasks** table:
-```json
-{
-  "task_id": 1,
-  "goal_id": 1,
-  "title": "Complete basics",
-  "desc": "Learn variables, loops, functions",
-  "status": "doing",
-  "start_time": "2026-05-08T10:00:00",
-  "finished_time": null,
-  "order": 1.0
-}
+```sql
+CREATE TABLE tasks (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    goal_id INTEGER NOT NULL,
+    title TEXT NOT NULL,
+    desc TEXT NOT NULL DEFAULT '',
+    status TEXT NOT NULL DEFAULT 'todo',
+    start_time TEXT,
+    finished_time TEXT,
+    "order" REAL NOT NULL DEFAULT 0.0,
+    FOREIGN KEY (goal_id) REFERENCES goals(id)
+);
 ```
 
-### 3.2 Database Initialization
-
-```python
-# database.py responsibilities:
-# - Initialize TinyDB with data/db.json
-# - Create tables: users, goals, tasks
-# - Seed admin user on first run (username: admin, password: admin123)
-# - Provide CRUD helper functions for each table
-```
+### 3.2 Database Initialization (schema.py)
+- `schema.py` defines SQL table creation and `get_connection()` helper
+- `init_db()` creates tables and seeds admin user on first run
+- Uses `sqlite3.Row` for dict-like row access
 
 ## 4. API Endpoints
 
@@ -426,6 +416,7 @@ uv add flask tinydb bcrypt
 - `pyproject.toml` (auto-generated by uv)
 - `uv.lock` (auto-generated by uv)
 - `config.py`
+- `schema.py`
 - `database.py`
 - `auth.py`
 - `app.py` (basic setup)
@@ -517,7 +508,7 @@ uv add flask tinydb bcrypt
 
 ```python
 # Database
-DB_PATH = "data/db.json"
+DB_PATH = "data/db.sqlite"
 
 # Default admin credentials
 DEFAULT_ADMIN_USERNAME = "admin"
@@ -559,7 +550,7 @@ PORT = 5000
 - Session-based authentication with HTTP-only cookies
 - CSRF protection (Flask-WTF or manual token)
 - Input sanitization (prevent XSS)
-- SQL injection not applicable (TinyDB), but validate all inputs
+- Parameterized SQL queries (sqlite3 placeholders prevent injection)
 - Rate limiting on auth endpoints (optional)
 - HTTPS in production
 
diff --git a/devdocs/v1/PRD.md b/devdocs/v1/PRD.md
index 20fcbaf..0b80a20 100644
--- a/devdocs/v1/PRD.md
+++ b/devdocs/v1/PRD.md
@@ -84,7 +84,7 @@ Tech Stack:
 
 - Backend: Python + Flask (lightweight, good for small apps)
 - Frontend: Vanilla JS + HTML/CSS (simple, no build step needed)
-- Database: TinyDB (single JSON file, perfect for this scale)
+- Database: SQLite (lightweight file-based relational database)
 - Authentication: Session-based with password hashing (bcrypt)
 - Drag-and-drop: HTML5 Drag and Drop API or SortableJS