The most popular data format on the web is arguably JSON. It is a simple and convenient format. Most web services allow to send and receive data in JSON.
Unfortunately, parsing JSON can be time and energy consuming. Back in 2019, we released the simdjson library. It broke speed records and it is still one of the most efficient and fast JSON parsing library. It makes few compromises. It provides exact float parsing, exact unicode validation and so forth.
There are many ways a library can give you access to the JSON data. A convenient approach is the DOM tree (DOM stands for document object model). In a DOM-based approach, the document is parsed entirely and materialized in an in-memory construction. For some applications, it is the right model, but in other instances, it is a wasteful step.
We also have streaming-based approaches. In such approaches, you have an event-based interface where the library calls user-provided function when encountering different elements. Though it can be highly efficient, in part because it sidesteps the need to construct a DOM tree, it is a challenging programming paradigm.