Innomerc Learn
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A worked example

Keep the saved page, or fetch a new one?

One exchange at a time. Read what changes, then explain it in your own words before moving on.

  1. Meet the components
  2. Follow the steps
  3. Compare an example
  4. Check your understanding
Interactive Lab

Keep the saved page, or fetch a new one?

Example: a browser has yesterday’s timetable. A validator helps the server compare versions.

Steps1. Saved validator 2. If-None-Match 3. 304 Not Modified
Click a box or choose its name to learn what it means.
BrowserReadyWeb serverReadySaved responseReadyBrowserReadyWeb serverReadySaved responseReady
Ready to tracePage unchanged
Before you start · 3 stepsPage unchanged

The browser validates its stored response and reuses the saved body.

How to use this example

Select Next step to read at your own pace, or Animate step to watch one exchange. Nothing advances until you choose.

Inspect components & read every step
  • Browser

    The program you use to open websites.

    Example: Your browser requests a web page and displays the response.

  • Web server

    Software that responds to requests for web content.

    Example: It sends a page or confirms that a saved representation remains unchanged.

  • Saved response

    A previously stored web response that may be reused if caching rules allow it.

    Example: The browser checks whether yesterday’s timetable is still current.

Page unchanged

The browser validates its stored response and reuses the saved body.

  1. Saved response Browser: Saved validator. The browser has a stored response with an ETag.
  2. Browser Web server: If-None-Match. A conditional GET asks whether this representation still matches.
  3. Web server Browser: 304 Not Modified. The server confirms a match without sending the full body.

Page changed

A different representation means the browser needs the new response body.

  1. Saved response Browser: Old validator. The browser has an earlier timetable response.
  2. Browser Web server: If-None-Match. The server compares the saved validator with the current version.
  3. Web server Browser: 200 + new body. The server sends the changed representation and relevant metadata.

Fictional teaching trace. One moving dot represents an exchange, not a measured network capture.