Lab 02: HTTP, API, Browser

See how browsers and APIs exchange messages.

HTTP is a postal system. The URL is the address. Headers are envelope metadata. The body is the letter. Status codes are delivery results.

1. Open any website in a browser.
2. Open developer tools and the Network tab.
3. Reload the page.
4. Pick one request and record:
   • URL
   • method
   • status
   • request headers
   • response headers
   • response body type
5. Use curl to request a public JSON API.
6. Save the response.
7. Change one request header and observe whether the response changes.
8. Write a tiny local API with one GET /health route and one POST /echo route.
9. Call both routes with curl.

curl -i https://example.com
curl -X POST http://localhost:3000/echo \
  -H 'Content-Type: application/json' \
  -d '{"message":"hello"}'

• What is the difference between a URL and an endpoint?
• What does a 404 mean?
• What does a 500 mean?
• Why should APIs validate request bodies?
• What should /health prove?

Create http-api-browser.md with:

• Screenshot or notes from browser Network tab.
• curl commands and responses.
• Local API code or link.
• Explanation of one failed request.

You can explain one real browser request and one local API request end to end.