protoc-gen-cli

Generate an API's command-line interface from its .proto.

grpcurl calls any gRPC server. You write each request body as JSON. protoc-gen-cli generates a CLI for one API instead:

• Each service becomes a command.
• Each RPC becomes a subcommand.
• Each request field becomes its own flag.
• Your proto comments become the help text.

The plugin runs under buf and protoc. It accepts proto2, proto3, and editions through 2024. The target option selects the language and the CLI library. gocobra generates Go with Cobra.

proto in, CLI out

This service and message:

// ShelfService manages shelves.
service ShelfService {
  // Create adds a shelf to the store.
  rpc Create(CreateShelfRequest) returns (Shelf) {}
}

message CreateShelfRequest {
  // The shelf to create.
  Shelf shelf = 1;
}

message Shelf {
  // A unique shelf id.
  int64 id = 1;
  // The shelf theme, for example "fiction".
  string theme = 2;
}

become this command:

$ bookstore shelf create --help
Create adds a shelf to the store.

Usage:
  bookstore shelf create [flags]

Flags:
  -h, --help                 help for create
      --shelf string         The shelf to create.
      --shelf.id int         A unique shelf id.
      --shelf.theme string   The shelf theme, for example "fiction".

Global Flags:
      --columns string         Table columns, as LABEL:path pairs into the JSON response.
                               Example: --columns 'ID:$.id,NAME:$.name'.
  -d, --data stringArray       A request body, inline.
      --dry-run                Print the assembled requests without sending them.
      --example                Print an example request body without sending it.
  -f, --filename stringArray   Request bodies from a file, or '-' for stdin.
  -o, --output string          Output format: json, jsonl, table, yaml.
                               Default: json on a terminal, jsonl when piped.
      --timeout duration       Per-call deadline (e.g. 30s, 2m); 0 means no deadline.

The command and flag descriptions above come from comments in the proto. The plugin writes only the global flags.

When to use it

Use protoc-gen-cli when you want an easy-to-maintain CLI for one API. It suits an API that changes often and your team calls every day.

Use grpcurl or buf curl instead when you want to poke an unfamiliar server once. They need no build step. They call any server through reflection.

The generated CLI never exposes gRPC to its users. It takes no -H flag and no target address. The caller owns the grpc.ClientConn. Transport, credentials, and interceptors stay there.

Install

brew install --cask braveokafor/tap/protoc-gen-cli

Or go install github.com/braveokafor/protoc-gen-cli/cmd/protoc-gen-cli@latest. The releases page also has archives for Linux, macOS, and Windows.

The Quickstart below runs all three plugins, so protoc-gen-go and protoc-gen-go-grpc go on PATH too:

go install google.golang.org/protobuf/cmd/protoc-gen-go@latest
go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest

Quickstart

The generated file holds only the command tree. It names the message types and the gRPC client stubs directly. Run all three plugins into the same package:

# buf.gen.yaml
version: v2
plugins:
  - local: protoc-gen-go
    out: gen
    opt: [paths=source_relative]
  - local: protoc-gen-go-grpc
    out: gen
    opt: [paths=source_relative]
  - local: protoc-gen-cli
    out: gen
    opt: [paths=source_relative, target=gocobra]
inputs:
  - directory: proto

Run buf generate. Under protoc, the same options go to --cli_out and --cli_opt:

protoc -I proto \
  --go_out=gen --go_opt=paths=source_relative \
  --go-grpc_out=gen --go-grpc_opt=paths=source_relative \
  --cli_out=gen --cli_opt=paths=source_relative,target=gocobra \
  proto/bookstore/v1/bookstore.proto

Then mount the generated constructors on a root command:

package main

import (
	"context"
	"errors"
	"log"
	"os"
	"os/signal"

	bookstorev1 "example.com/quickstart/gen/bookstore/v1"
	"github.com/spf13/cobra"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"
)

func main() {
	conn, err := grpc.NewClient("localhost:8080",
		grpc.WithTransportCredentials(insecure.NewCredentials()))
	if err != nil {
		log.Fatal(err)
	}

	root := &cobra.Command{Use: "bookstore"}
	root.AddCommand(bookstorev1.NewShelfServiceCommand(conn))

	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt)
	defer stop()

	if err := root.ExecuteContext(ctx); err != nil {
		var coded interface{ ExitCode() int }
		if errors.As(err, &coded) {
			os.Exit(coded.ExitCode())
		}
		os.Exit(1)
	}
}

go build gives you the CLI above. The plugin generates no main and no root command.

A service command takes the name of its service, minus a -service suffix. Pick a root name that differs from it, because a root named shelf here produces shelf shelf create.

You can also rename the command from the proto. See Annotations.

What your users get

• Flags. A scalar field becomes its own flag. A field of a message field becomes a dotted flag such as --shelf.theme, down to request-expand-depth. A repeated field repeats. A map field takes key=value.

• Whole-request input. -f/--filename reads a file or - for stdin. -d/--data takes a request body inline. Both repeat, and both apply before the flags. JSON and YAML are the built-in formats. The caller adds more. A source holds one body or many: JSON Lines, a JSON array, or a YAML file with --- separators. An rpc that sends one request merges them with proto.Merge.

• --example. Flags reach the top of a request. A field deeper than request-expand-depth has no flag of its own. A nested request otherwise needs a hand-written body. --example prints the whole shape, filled in and ready to edit. The server accepts it as a request. It round-trips:

  $ bookstore shelf create --example | bookstore shelf create -f -

• Output formats. -o/--output selects a format. The built-ins are json, jsonl, yaml, and table. The caller adds one, removes one, and sets a different default. With no -o, output is json on a terminal and jsonl in a pipe. A table column reads a response field, or a field below one down to response-expand-depth. A repeated message field becomes its own titled sub-table. --columns 'ID:$.id,TITLE:$.title' names the table columns for one run, and selects table on its own.

• Shell completion. Cobra gives your root completion bash|zsh|fish|powershell. Enum flags complete their values.

• Streaming. A server-streaming command prints each response as it arrives. A client-streaming command sends one request for each body, as it reads it, so -f catalogue.jsonl and producer | bookstore … -f - both stream. Nothing reads stdin unless -f - names it.

• Exit codes. 0 success. 2 a wrong invocation. 124 a deadline. 130 an interrupt. 1 everything else, including a failed call. The CLI removes the rpc error: wrapper from the message.

• --timeout and --dry-run. --timeout sets a deadline for each call. --dry-run prints the assembled requests and sends nothing.

Options

Pass these in opt:.

Option	Default	Meaning
target	(required)	The target to generate with. gocobra is Go with Cobra.
request-expand-depth	1	How many message levels below a request field still get their own dotted flags.
response-expand-depth	1	How many message levels below a response field still get their own table columns.
templates	(built-in)	A directory of *.tmpl files. Each {{define}} block replaces the built-in fragment of the same name.
dump-ir	false	Also write <file>.cli.ir.json for each file. This dump is a debugging aid.

Configure from the proto

Import the cli.v1 schema and annotate the proto. The CLI then needs nothing from the caller. The proto renames a command, deprecates it, adds a shorthand, or declares table columns.

# buf.yaml
version: v2
modules:
  - path: proto
deps:
  - buf.build/braveokafor/protoc-gen-cli

Run buf dep update to resolve it, then annotate:

import "cli/v1/cli.proto";

service BookstoreService {
  option (cli.v1.service).name = "catalog";

  rpc CreateBook(CreateBookRequest) returns (Book) {
    option (cli.v1.command).name = "add";
  }
}

message Book {
  int64 id = 1 [(cli.v1.param).skip = true];
  string author = 2 [(cli.v1.param).shorthand = "a"];
  string title = 3 [(cli.v1.param).shorthand = "t", (cli.v1.param).help = "Title to print on the spine."];
}

Under protoc, the release archive has proto/cli/v1/cli.proto. Add the archive's proto/ directory to your -I path.

examples/bookstore-annotated configures a whole CLI this way. Annotations documents every field.

Next steps

Read the guide. It takes the quickstart above. It finishes with a configured two-service CLI and a complete main.go.

Then go straight to the task you have:

I want to	Read
Rename or deprecate a command, add a shorthand, override the help text	Annotations
Set the default output, add an output or input format, choose table columns	The gocobra target
Know what text a timestamp, duration, Any or nested message takes	Field types
See what my users get: flags, merge order, completion, exit codes	The generated CLI
Fix a warning, an error, or a missing flag	Troubleshooting

Examples

Each example holds a proto, the generated code, a stub server, and a main.go. Each one runs.

• bookstore. A plain proto. The caller does the configuration.
• bookstore-annotated. The same API, configured from the proto.
• kitchen-sink. Every field type, every RPC shape, and the edge cases.

Versioning and compatibility

Releases follow Semantic Versioning.

Every generated header records the plugin version. protoc-gen-cli -version prints it. A local go build reads dev.

Contributing

See CONTRIBUTING.md. Run make all before you open a pull request. Write Conventional Commits.

License

MIT.