Style Guide

This is our Style Guide for Protobuf.

This document is purposefully concise, and is meant as a short reference for developers to refer to when writing Protobuf schemas.

The requirements follow the DEFAULT lint category. For details on each rule and it's rationale, see that documentation. Within this Style Guide, we provide links under (Why?) where relevant for each check.

The recommendations are not enforced, but are rather for reference. Some of the recommendations will be incorporated into the STRICT category.

This Style Guide is designed to provide consistency and maintainability across a Protobuf schema of any size and any purpose, but without being so opinionated as to restrict organizations from making the design decisions they need to make for their individual APIs. We will provide a Strict Style Guide for those who want a set of rules to provide further consistency across their Protobuf schema. This will include items like file ordering, documentation, and field naming.

Requirements#

Files and Packages#

All files should have a package defined. (Why?)

All files of the same package should be in the same directory. All files should be in a directory that matches their package name. (Why?) For example, assuming we have a single root proto:

.
└── proto
    └── foo
        └── bar
            ├── bat
            │   └── v1
            │       └── bat.proto // package foo.bar.bat.v1
            └── baz
                └── v1
                    ├── baz.proto         // package foo.bar.baz.v1
                    └── baz_service.proto // package foo.bar.baz.v1

Packages should be lower.snake_case. (Why?)

The last component of a package should be a version. (Why?)

Files should be named lower_snake_case.proto (Why?)

The following file options should have the same value, or all be unset, for all files that have the same package: (Why?)

csharp_namespace
go_package
java_multiple_files
java_package
php_namespace
ruby_package
swift_prefix

For example, if we have file foo_one.proto:

// foo_one.proto
syntax = "proto3";

package foo.v1;

option go_package = "foov1";
option java_multiple_files = true;
option java_package = "com.foo.v1";

Another file foo_two.proto with package foo.v1 must have these three options set to the same value, and the other options unset:

// foo_two.proto
syntax = "proto3";

package foo.v1;

option go_package = "foov1";
option java_multiple_files = true;
option java_package = "com.foo.v1";

Imports#

No imports should be declared as public or weak. (Why?)

Enums#

Enums should not have the allow_alias option set. (Why?)

Enum names should be PascalCase. (Why?)

Enum value names should be UPPER_SNAKE_CASE. (Why?)

Enum value names should be prefixed with the UPPER_SNAKE_CASE of the enum name. (Why?). For example, given the enum FooBar, all enum value names should be prefixed with FOO_BAR_.

The zero value for all enums should be suffixed with _UNSPECIFIED. (Why?) The suffix is configurable for Buf linting. For example, given the enum FooBar, the zero value should be FOO_BAR_UNSPECIFIED = 0;.

Messages#

Message names should be PascalCase. (Why?)

Field names should be lower_snake_case. (Why?)

Oneof names should be lower_snake_case. (Why?)

Field names should not be any capitalization of "descriptor", with any number of prefix or suffix underscores. (Why?). For example, all of the following should not be field names:

// ALL FIELDS ARE INVALID
message Foo {
  string descriptor = 1;
  string Descriptor = 2;
  string descRiptor = 3;
  string _descriptor = 4;
  string __descriptor = 5;
  string descriptor_ = 6;
  string descriptor__ = 7;
  string __descriptor__ = 8;
}

Services#

Service names should be PascalCase. (Why?)

Service names should be suffixed with Service. (Why?) The suffix is configurable for Buf linting.

RPC names should be PascalCase. (Why?)

All RPC request and responses messages should be unique across your Protobuf schema. (Why?)

All RPC request and response messages should be named after the RPC, either by naming them MethodNameRequest, MethodNameResponse or ServiceNameMethodNameRequest, ServiceNameMethodNameResponse. (Why?)

Recommendations#

While not strictly related to style, set up breaking change detection and do not break your Protobuf schema. See the breaking change detector documentation for more details on how to enforce this with Buf.

Use // instead of /* */ for comments.

Over-document, and use complete sentences for comments. Put documentation above the type, instead of inline.

Avoid widely-used keywords for all types, especially packages. For example, if your package name is foo.internal.bar, the internal component will block importing the generated stubs in other packages for Golang.

Files should be ordered in the following manner (this matches Google's current recommendations):

License header (if applicable)
File overview
Syntax
Package
Imports (sorted)
File options
Everything else

Used pluralized names for repeated fields.

Name fields after their type as much as possible. For example, for a field of message type FooBar, name the field foo_bar unless there is a specific reason to do otherwise.

Avoid using nested enums and nested messages. You may end up wanting to use them outside of their context message in the future, even if you do not think so at the moment.

While controversial, our recommendation is to avoid streaming RPCs. While they certainly have specific use cases that make them extremely valuable, on the whole they generally cause a lot of problems, push RPC framework logic up the stack, and usually prevent developing more reliable architectures.