The Site Experience enables comprehensive technical analysis of a website. For this purpose, crawls are set up, which charge page credits. The number of page credits required depends on the respective settings in the crawl (see: How do I set up a crawl?). For example, a JavaScript crawl is more extensive and therefore costs more credits.
How many credits actually have to be raised for a crawl can only be guessed in advance. If all settings in the crawl setup are done, an estimation of the required page credits is provided in the right field.
How many page credits do I have left? When do they fill up again?
You can find an overview of your available resources under Settings > Licenses > Overview.
There you can also see the start date of the license period. That indicates when the credits will be recharged. For example, the license started on 03/05/2019. This means that the credits refill every month on the 05th.