Using the Google AMP Cache

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Introduction

The Google AMP Cache stores valid AMPs and provides a consistently fast access to AMPs. It is available for anyone to use.

This article describes the new AMP URL Cache format which will go live in Q1 2017. For the current format please refer to the official documentation.

AMP Cache URL Format

When possible, the Google AMP Cache will create a subdomain for each AMP document's domain by first converting it from IDN (punycode) to UTF-8. The caches replaces every - (dash) with -- (2 dashes) and replace every . (dot) with - (dash). For example, pub.com will map to pub-com.cdn.ampproject.org.

Here is AMP Cache URL for https://ampbyexample.com/components/amp-img:

The converted AMP Cache URL consists of the following parts:

  • ampbyexample-com: the publisher domain converted into a subdomain using the algorithm described above.
  • cdn.ampproject.org: the AMP Cache domain.
  • c: to indicate that it's an AMP document (there is also i for image and r for resources such as fonts).
  • s: indicating that the AMP Cache fetches the content from the origin using TLS (secure HTTPS).
  • ampbyexample.com/components/amp-img: the original URL excluding the scheme.

It is OK for URLs to include parameters in the query string, simply include these in the AMP Cache URL as well.

Example: https://ampbyexample-com.cdn.ampproject.org/ampbyexample.com/g?value=Hello%20World.

Redirect & Error Handling

Here are some examples for how the AMP Cache handles redirects and errors:

Redirects

The AMP Cache follows redirects when resolving AMP URLs. For example, if an URL redirects to another AMP URL:

$ curl -I https://ampbyexample.com/amp-img.html

HTTP/1.1 301 Moved Permanently
Content-Type: text/html; charset=utf-8
Location: https://ampbyexample.com/components/amp-img/
...

Then the AMP Cache will return the content of the resolved redirect for the original URL.

Example: https://ampbyexample-com.cdn.ampproject.org/ampbyexample.com/amp-img.html.

Important: if you move the location of the AMP Files on your server, make sure to set up a redirect from the old location to the new one.

Not Found

When a page is not found in the AMP Cache, it will show an error page and return a 404 status.

Example: https://ampbyexample-com.cdn.ampproject.org/ampbyexample.com/not-found

Invalid AMP

When a page is invalid AMP, the AMP Cache will return a 404 status.

Example: https://ampbyexample-com.cdn.ampproject.org/ampbyexample.com/invalid_amp.html

Server Errors

If an URL returns a 5XX server errors, the AMP Cache will return a 404 status.

Example: https://ampbyexample-com.cdn.ampproject.org/ampbyexample.com/error