Extracting Google PageSpeed performance score in .NET

Most webmasters are aware that Google uses performance as a ranking signal for both desktop and mobile searches so its important your site is as fast as it can be. You can check your performance score according to Google in Chrome developer tools or online but since they provide a HTTP API you can get also get performance scores programmatically.

Calling the PageSpeed HTTP API and Serializing the JSON response into a DTO

Calling the API is easy as its a simple GET request as can be seen below…

How to call the PageSpeed API

You just need to make sure you set your key (you can get one from here but a key is not needed if your just testing) and the URL which you want to run the performance check for as query params. You can see above I’ve also set strategy which will default to ‘DESKTOP’ if not set.

After the response comes back (not very fast as the performance check takes a few seconds) I use the new System.Text.Json serializer released in .NET Core 3.0 to convert it into a simple DTO which matches the structure of the JSON. The performance score itself is located in lighthouseResult -> categories -> performance -> score.

As you can see to adhere with VS naming conventions I’ve made the properties start with uppercase and therefore needed to set the PropertyNameCasesInsentive flag above as otherwise the DTO would be empty after serialization.

Simple DTO for storing PageSpeed results

Calling the PageSpeed HTTP API and querying the JSON directly using JsonDocument

The above is nice and neat as we now have a strongly typed object which we could pass to our views etc. In this case however we only care about one property, the performance score itself so having to create a nested class or DTO just for this seems like a lot of effort.

Rather than serializing we can alternatively use JsonDocument and query the JSON string directly by chaining a couple of GetProperty calls together.

Use GetProperty to read JSON properties

Of course to use GetProperty you need to be sure the property will always exist in your JSON as otherwise an exception will be thrown. If your not sure about this use TryGetProperty instead and check if you’ve successfully got an element before moving on…

Use TryGetProperty to read JSON properties

Google PageSpeed Insights API Client Library for .NET

Google also has a PageSpeed API Client Library for .NET however I’ve not really looked into it much yet. Using this library over simple HTTP requests should allow you to have a more strongly typed approach where you don’t have to worry about matching JSON property names etc.

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