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# What is a proto file?

A .proto file is a file used to define a Protocol Buffer message type. Protocol Buffers is a language- and platform-neutral data serialization format developed by Google. It is commonly used for communication between different systems and programming languages, as well as for data storage and data exchange.

In a .proto file, you define the structure of your message using a simple language called the Protocol Buffer Language. This includes defining the fields of the message, their data types, and any options or constraints that apply to them. You can also define nested message types and enumerations within the file.

Once you have defined your message type in a .proto file, you can use the Protocol Buffer compiler to generate code in various programming languages (such as Java, C++, Python, and others) that you can use to create, read, and write Protocol Buffer messages in your code.

Proto example

    syntax = "proto3";

    message Person {
      string name = 1;
      int32 age = 2;
      repeated string email = 3;
    }

In this example, the .proto file specifies that a Person message will have three fields:

- name is a string with a field number of 1
- age is an integer with a field number of 2
- email is a repeated string (meaning it can occur multiple times) with a field number of 3.
- The syntax = "proto3" line specifies that this .proto file is using version 3 of the Protocol Buffers syntax.

# Alternative

- There is an alternative way for writing proto files first : code first grpc It adds code-first support to `Grpc.AspNetCore` and `Grpc.Net.Client`. It uses .NET types annotated with attributes to define an app's gRPC services and messages.

`builder.Services.AddCodeFirstGrpc();` https://learn.microsoft.com/en-us/aspnet/core/grpc/code-first?view=aspnetcore-7.0