When you first review your Third Party synthetic dashboard you'll want to double check that resources have been grouped correctly.
We use the URL you're testing to identify the first party domain and any sub domains. So if you're testing "website.com" we'll also include any subdomains like "cdn.website.com" as a first party.
All other requests will either be identified as a known third party service or will be lumped together into the "Unrecognized Third Party" group. There's a good chance there might be other domains in that group that you consider first party. You can move resources into the first party group by adding them to Settings > First Party.
Unrecognized Third Party
We use the open source project third-party-web to identify known third party services. If there are other popular third party services that you think should be recognized but aren't you can let SpeedCurve support know or contribute them directly to the project.
Custom Third Party
In Settings > Third Party you can also build your own custom third party with a set of filters that match on the URL or your resources.
A custom third party is actually just a group of resources and doesn't have to be strictly used for tracking a third party. You could track just one resource like a single JS resource "bundle.js" if you wanted to and also set performance budgets on it.
Third Party Performance Budgets
Once you have all your resources grouped you can track any of them you like. Any third party listed under Settings > Third Party is automatically tracked over time. The waterfall chart at the bottom of the Third Party dashboard makes it really easy to toggle tracking on and off for any other third party you see.
You'll then get extra charts at the top of the Third Party dashboard for the third parties you're tracking over time.
And in your Favourites dashboard you'll be able to set performance budgets and get alerts on any of the third party metrics.
So first check the grouping of your third parties, then start tracking them and set performance budgets to track their impact on your user experience!