[sanderjd]

The most common use cases line up with those of JSON: communication between programs that don't share an address space. The main advantage over JSON (in my opinion) is the definition of an explicit schema. The second (and also important) advantage is in the efficient size of the serialized data, which limits memory, disk, and bandwidth usage. Another (less important to me) advantage is in serialization and deserialization efficiency. A disadvantage is that it requires deserialization for human inspection - that is, it isn't plain text like JSON or XML.

It is similar to Apache Thrift, if you're looking for a non-Google project with similar ideas.

[euyyn]

Serialization and deserialization efficiency is specially important for mobile apps, in which the CPU used to parse/serialize JSON (or gzipped JSON) can become very prominent.

Apache Thrift, IIRC, is actually a reimplementation of protos, in the same way that Facebook's Buck is of Google's Bazel.

I have some times looked at "raw" binary protos to inspect the string fields, that happen(ed?) to be byte-aligned and so readable in a text editor. Not sure off the top of my head if that's always the case.