ISPs block access to websites around the world. In India, the Government issues a secret orders to ISPs with a list of websites to block.
ISPs implement these blocks in various ways, and at various times. There is no transparency in the process. Right now we only know about websites being blocked when:
A way for people to submit a website that’s blocked, and have a distributed test that’s run for the availability of that site on various networks.
We can also run these tests periodically over time.