Let's talk about Quota and Cost based Quota of an API

What is a an API in short and simple terms?

Application Programming Interface (APIs) are messengers which take requests from the user and give them to the system, they then take the response generated by the system and deliver it back to the user.
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Quota

API Quota means the number of requests an user is allowed to make over a period of time.
Why we need Quota's?
APIs run on servers and servers can only respond to a limited number of requests in a given time. To make sure that everyone can use the API service the creator of an API need to set a limit to how many requests an API user makes. Normally the limit can be from per minute to per day.
Here is an example of Google's Calendar API

Cost Based Quota

Before you start to think that the cost may be related to money you would be happy to hear that it is not.
For understanding cost-based quota you need to consider quota as points allotted to a user.
In cost-based quota systems each request you make against an API costs you some points, these points are then subtracted from your daily quota limit. There are different resource methods and each method has a cost associated with it.

Google's Youtube API
Google's Youtube API is the best example of Cost Based Quota system.
Here is the daily quota limit for YouTube Data API v3

Costs for different resource methods:
A read operation that retrieves a list of resources(channels, videos, playlists) usually costs 1 unit.
A write operation that creates, updates, or deletes a resource usually has costs 50 units.
A search request costs 100 units.
A video upload costs 1600 units.

I hope you got it🙃,Thanks for reading.