diff --git a/app/__init__.py b/app/__init__.py
new file mode 100644
index 00000000..74923076
--- /dev/null
+++ b/app/__init__.py
@@ -0,0 +1,25 @@
+from flask import Flask
+from sqlalchemy import create_engine
+from sqlalchemy.orm import scoped_session, sessionmaker
+from sqlalchemy.ext.declarative import declarative_base
+
+engine = create_engine('sqlite:///database.db', echo=True)
+db_session = scoped_session(sessionmaker(bind=engine))
+
+Base = declarative_base()
+Base.query = db_session.query_property()
+
+def create_app():
+    app = Flask(__name__)
+
+    from .routes import notes_bp, tags_bp, comments_bp
+    app.register_blueprint(notes_bp)
+    app.register_blueprint(tags_bp)
+    app.register_blueprint(comments_bp)
+
+    @app.teardown_appcontext
+    def shutdown_session(exception=None):
+        db_session.remove()
+
+    Base.metadata.create_all(bind=engine)
+    return app
diff --git a/app/models.py b/app/models.py
new file mode 100644
index 00000000..7d70f6e9
--- /dev/null
+++ b/app/models.py
@@ -0,0 +1,31 @@
+from . import Base
+from sqlalchemy import Column, Integer, String, Text, Table, ForeignKey, DateTime
+from sqlalchemy.orm import relationship
+import datetime
+
+note_tag = Table(
+    'note_tag', Base.metadata,
+    Column('note_id', Integer, ForeignKey('notes.id')),
+    Column('tag_id', Integer, ForeignKey('tags.id'))
+)
+
+class Note(Base):
+    __tablename__ = 'notes'
+    id = Column(Integer, primary_key=True)
+    title = Column(String(100))
+    content = Column(Text)
+    tags = relationship('Tag', secondary=note_tag, back_populates='notes')
+
+class Tag(Base):
+    __tablename__ = 'tags'
+    id = Column(Integer, primary_key=True)
+    name = Column(String(50), unique=True)
+    notes = relationship('Note', secondary=note_tag, back_populates='tags')
+
+class Comment(Base):
+    __tablename__ = 'comments'
+    id = Column(Integer, primary_key=True)
+    content = Column(Text, nullable=False)
+    post_id = Column(Integer, ForeignKey('notes.id'), nullable=False)
+    created_at = Column(DateTime, default=datetime.datetime.utcnow)
+    note = relationship('Note', backref='comments')
diff --git a/app/routes.py b/app/routes.py
new file mode 100644
index 00000000..8b5d81ed
--- /dev/null
+++ b/app/routes.py
@@ -0,0 +1,111 @@
+from flask import Blueprint, request, jsonify
+from .models import Note, Tag, note_tag, Comment
+from . import db_session
+
+notes_bp = Blueprint('notes', __name__, url_prefix='/api/notes')
+tags_bp = Blueprint('tags', __name__, url_prefix='/api/tags')
+comments_bp = Blueprint('comments', __name__, url_prefix='/api/comments')
+
+@notes_bp.route('/', methods=['GET'])
+def get_notes():
+    notes = db_session.query(Note).all()
+    return jsonify([{'id': n.id, 'title': n.title, 'content': n.content} for n in notes])
+
+@notes_bp.route('/', methods=['POST'])
+def create_note():
+    data = request.json
+    new_note = Note(title=data['title'], content=data['content'])
+    db_session.add(new_note)
+    db_session.commit()
+    return jsonify({'message': 'Note created'}), 201
+
+@notes_bp.route('/<int:note_id>', methods=['PUT'])
+def update_note(note_id):
+    data = request.json
+    note = db_session.query(Note).get(note_id)
+    if not note:
+        return jsonify({'error': 'Note not found'}), 404
+    note.title = data['title']
+    note.content = data['content']
+    db_session.commit()
+    return jsonify({'message': 'Note updated'})
+
+@notes_bp.route('/<int:note_id>', methods=['DELETE'])
+def delete_note(note_id):
+    note = db_session.query(Note).get(note_id)
+    if not note:
+        return jsonify({'error': 'Note not found'}), 404
+    db_session.delete(note)
+    db_session.commit()
+    return jsonify({'message': 'Note deleted'})
+
+@tags_bp.route('/', methods=['POST'])
+def create_tag():
+    data = request.json
+    tag = Tag(name=data['name'])
+    db_session.add(tag)
+    db_session.commit()
+    return jsonify({'message': 'Tag created', 'id': tag.id}), 201
+
+@tags_bp.route('/', methods=['GET'])
+def get_tags():
+    tags = db_session.query(Tag).all()
+    return jsonify([{'id': t.id, 'name': t.name} for t in tags])
+
+@tags_bp.route('/<int:tag_id>', methods=['PUT'])
+def update_tag(tag_id):
+    data = request.json
+    tag = db_session.query(Tag).get(tag_id)
+    if not tag:
+        return jsonify({'error': 'Tag not found'}), 404
+    tag.name = data['name']
+    db_session.commit()
+    return jsonify({'message': 'Tag updated'})
+
+@tags_bp.route('/<int:tag_id>', methods=['DELETE'])
+def delete_tag(tag_id):
+    tag = db_session.query(Tag).get(tag_id)
+    if not tag:
+        return jsonify({'error': 'Tag not found'}), 404
+    db_session.delete(tag)
+    db_session.commit()
+    return jsonify({'message': 'Tag deleted'})
+
+@comments_bp.route('/', methods=['POST'])
+def create_comment():
+    data = request.json
+    comment = Comment(content=data['content'], post_id=data['post_id'])
+    db_session.add(comment)
+    db_session.commit()
+    return jsonify({'message': 'Comment created', 'id': comment.id}), 201
+
+@comments_bp.route('/', methods=['GET'])
+def get_comments():
+    post_id = request.args.get('post_id')
+    query = db_session.query(Comment)
+    if post_id:
+        query = query.filter_by(post_id=post_id)
+    comments = query.all()
+    return jsonify([
+        {'id': c.id, 'content': c.content, 'post_id': c.post_id, 'created_at': c.created_at.isoformat()}
+        for c in comments
+    ])
+
+@comments_bp.route('/<int:comment_id>', methods=['PUT'])
+def update_comment(comment_id):
+    data = request.json
+    comment = db_session.query(Comment).get(comment_id)
+    if not comment:
+        return jsonify({'error': 'Comment not found'}), 404
+    comment.content = data['content']
+    db_session.commit()
+    return jsonify({'message': 'Comment updated'})
+
+@comments_bp.route('/<int:comment_id>', methods=['DELETE'])
+def delete_comment(comment_id):
+    comment = db_session.query(Comment).get(comment_id)
+    if not comment:
+        return jsonify({'error': 'Comment not found'}), 404
+    db_session.delete(comment)
+    db_session.commit()
+    return jsonify({'message': 'Comment deleted'})
diff --git a/database.db b/database.db
new file mode 100644
index 00000000..7cdd4d4f
Binary files /dev/null and b/database.db differ
diff --git a/models.py b/duplicate_models.py
similarity index 100%
rename from models.py
rename to duplicate_models.py
diff --git a/run.py b/run.py
new file mode 100644
index 00000000..a3fdaf3c
--- /dev/null
+++ b/run.py
@@ -0,0 +1,6 @@
+from app import create_app
+
+app = create_app()
+
+if __name__ == '__main__':
+    app.run(debug=True)
diff --git a/test_api.py b/test_api.py
new file mode 100644
index 00000000..327ae191
--- /dev/null
+++ b/test_api.py
@@ -0,0 +1,43 @@
+import pytest
+import json
+import sys
+import os
+
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+from app import create_app
+
+@pytest.fixture
+def client():
+    app = create_app()
+    app.config['TESTING'] = True
+    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///:memory:'  # Use in-memory DB for tests
+    with app.test_client() as client:
+        with app.app_context():
+            yield client
+
+def test_post_note(client):
+    payload = {"title": "Test Note", "content": "This is a test note."}
+    response = client.post("/api/notes/", data=json.dumps(payload), content_type="application/json")
+    assert response.status_code == 201
+    assert b'Note created' in response.data
+
+def test_get_notes(client):
+    # Ensure at least one note exists
+    client.post("/api/notes/", data=json.dumps({"title": "Temp", "content": "Temp"}), content_type="application/json")
+    response = client.get("/api/notes/")
+    assert response.status_code == 200
+    assert isinstance(response.get_json(), list)
+
+def test_update_note(client):
+    # Create a note first
+    client.post("/api/notes/", data=json.dumps({"title": "Temp", "content": "Temp"}), content_type="application/json")
+    response = client.put("/api/notes/1", data=json.dumps({"title": "Updated", "content": "Updated"}), content_type="application/json")
+    assert response.status_code == 200
+    assert b'Note updated' in response.data
+
+def test_delete_note(client):
+    # Create a note first
+    client.post("/api/notes/", data=json.dumps({"title": "Temp", "content": "Temp"}), content_type="application/json")
+    response = client.delete("/api/notes/1")
+    assert response.status_code == 200
+    assert b'Note deleted' in response.data
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/test_api.py b/tests/test_api.py
new file mode 100644
index 00000000..3d30eba6
--- /dev/null
+++ b/tests/test_api.py
@@ -0,0 +1,40 @@
+import pytest
+import json
+import sys
+import os
+
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+from app import create_app()
+
+@pytest.fixture
+def client():
+    app = create_app()
+    app.config['TESTING'] = True
+    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///:memory:'  # Use in-memory DB for tests
+    with app.test_client() as client:
+        with app.app_context():
+            yield client
+
+def test_post_note(client):
+    payload = {"title": "Test Note", "content": "This is a test note."}
+    response = client.post("/api/notes/", data=json.dumps(payload), content_type="application/json")
+    assert response.status_code == 201
+    assert b'Note created' in response.data
+
+def test_get_notes(client):
+    client.post("/api/notes/", data=json.dumps({"title": "Temp", "content": "Temp"}), content_type="application/json")
+    response = client.get("/api/notes/")
+    assert response.status_code == 200
+    assert isinstance(response.get_json(), list)
+
+def test_update_note(client):
+    client.post("/api/notes/", data=json.dumps({"title": "Temp", "content": "Temp"}), content_type="application/json")
+    response = client.put("/api/notes/1", data=json.dumps({"title": "Updated", "content": "Updated"}), content_type="application/json")
+    assert response.status_code == 200
+    assert b'Note updated' in response.data
+
+def test_delete_note(client):
+    client.post("/api/notes/", data=json.dumps({"title": "Temp", "content": "Temp"}), content_type="application/json")
+    response = client.delete("/api/notes/1")
+    assert response.status_code == 200
+    assert b'Note deleted' in response.data