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Key Words

When you open a web page, your browser sends a request to a server. The server sends back a response, such as an HTML page.

URL​

A URL is the address of a resource, such as a page or an image.

Example: https://httpbin.org/get?category=books

  • https: the protocol used to communicate.
  • httpbin.org: the website's domain name.
  • /get: the path to the resource.
  • ?category=books: query string parameters; here, we send category with the value books.

httpbin is a service for testing HTTP requests. This endpoint returns JSON showing what you sent; it does not search for actual books.

HTTP Methods​

The method tells the server what you want to do.

  • GET: retrieve data. Example: open a product page or search for books.
  • POST: send data for the server to process. Example: submit data through a form.

Headers​

Headers contain extra information about a request or response.

  • User-Agent: information about the client making the request, such as a browser.
  • Content-Type: describes the format of the message body, such as text/html or application/json.

Cookies​

Cookies are small pieces of data that a website asks your browser to store. The browser sends matching cookies with later requests.

Example: After you log in, a session cookie can help the website recognize you when you open another page.

Request Data: Query Parameters and Payload​

You can send information to a server in the URL or in the request body.

  • Query string parameters appear after ? in the URL. Use & to separate multiple parameters.
    • Example: https://httpbin.org/get?q=python&page=2 sends two parameters: q=python and page=2.
    • Open the link and look for "args" in the JSON response. Change the values in the URL to see how the response changes.
  • Payload usually means data in the request body. Two common formats are:
    • Form data: fields submitted by a form, such as username=alice.
    • JSON: structured data, such as {"keyword": "python", "page": 2}.

Query parameters and a request body can be used together. A POST request can include both.

Developer Tools (Google Chrome)​

Use Google Chrome for this course so everyone can follow the same interface and steps.

Chrome Developer Tools (DevTools) let you inspect a page and the requests it makes. Open a website in Chrome, right-click the page, and choose Inspect to open DevTools.

  • Elements: inspect the page's current HTML structure. Use this to find a title, link, or table you want to collect.
  • Network: inspect requests and responses. Open this tab, refresh the page, and select a request to see its URL, method, headers, cookies, and data.