Interview Challenge: URL Shortener (Django + DRF)

Timed exercise for building a small app with AI assistance allowed.

Rules

• You may use AI tools freely (Cursor, ChatGPT, Copilot, etc.).
• You must be able to explain every line you keep.
• Prefer a small working slice over unfinished extras.
• Time box: ~60 minutes for a working happy path.

Goal

Build a URL shortener API with Django and Django REST Framework.

Required

1. POST /api/shorten/ — accept a long URL, return a short code / short URL
2. GET /<code>/ — redirect to the original URL
3. Persist links across process restart (SQLite is already configured)
4. Reject non-http / non-https URLs (including javascript:, empty, nonsense)

Nice to have (only after required works)

• Basic test(s) for create + redirect + invalid URL
• Unknown short code returns 404
• Simple click counter or expiry

Out of scope

• Auth, custom domains, analytics dashboards, Redis, Docker, deployment

Setup

python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt
python manage.py migrate
python manage.py runserver

Starter layout

config/          # Django project settings / urls
shortener/       # Your app — implement models, serializers, views, urls

Stub endpoints are wired but intentionally unfinished. Fill them in.

Suggested demo script (end of interview)

# create
curl -s -X POST http://127.0.0.1:8000/api/shorten/ \
  -H 'Content-Type: application/json' \
  -d '{"url":"https://example.com"}'

# visit the returned short URL in a browser (or curl -i) and confirm redirect

# reject bad schemes
curl -s -X POST http://127.0.0.1:8000/api/shorten/ \
  -H 'Content-Type: application/json' \
  -d '{"url":"javascript:alert(1)"}'

# restart the server, then confirm the short link still works

Deliverable

• Runnable app
• Short note in this README (or a NOTES.md) with:
  • how to run
  • how you tested
  • one known limitation