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What is Cache-Control?

In one sentence: An HTTP header that tells browsers and other caches how long a saved copy may be reused without checking again.

A little more

Cache-Control is the main header that sets a file's shelf life. max-age=60 means a browser may reuse the copy for sixty seconds without asking again.

Builders often give HTML a short max-age and give hashed CSS or images a long one, so updates reach people quickly while repeat visits stay fast.

See it in action

  1. BonusWhy does the website still show the old picture?Compare the logo on a pretend server with the copy on your browser shelf.6 min · interactive
  2. 3Can a website get tired?Why websites slow down or fall over when too many people visit at once.7 min · interactive

Related words

  • Cache A store of answers kept nearby so they don't have to be worked out or fetched again.
  • ETag A fingerprint of a file the server sends so a browser can ask later whether that exact copy has changed.
  • HTTP / HTTPS The way browsers and servers talk. HTTPS is the encrypted version.

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