protocli

proto-cli

Automatically generate production-ready CLI applications from your gRPC service definitions.

proto-cli is a protoc plugin that transforms Protocol Buffer service definitions into feature-rich command-line interfaces. Define your API once, get a complete CLI with proper flag handling, configuration management, lifecycle hooks, and both local and remote execution.

📦 Available on Buf Schema Registry: Import CLI annotations directly in your proto files:

deps:
  - buf.build/fernet/proto-cli

Features

Core Capabilities

• Zero Boilerplate - Define services in .proto, generate complete CLIs automatically
• Type-Safe Generation - Clean, idiomatic Go code via jennifer
• Dual Execution Modes - Run in-process (direct calls) or remote (gRPC client)
• Streaming Support - Server-side streaming RPCs with line-delimited output (NDJSON, YAML)
• Multi-Service CLIs - Organize multiple services under one CLI with nested commands

Configuration & Customization

• Configuration Loading - YAML/JSON config files with environment variable overrides
• Optional Fields - Full proto3 optional field support with explicit presence tracking
• Custom Deserializers - Transform CLI flags into complex proto messages
• Lifecycle Hooks - Before/after command execution, daemon startup/ready/shutdown
• gRPC Interceptors - Add unary and stream interceptors for logging, auth, metrics

Output & Display

• Multiple Formats - JSON, YAML, and Go-native formatting built-in
• Template Formats - Create custom formats using Go text templates
• Format-Specific Flags - Custom flags per format (e.g., --pretty for JSON)
• Streaming Output - NDJSON for JSON, document-delimited for YAML

Service Management

• Flat Command Structure - Hoist service commands to root level for single-service CLIs
• Selective Service Enable - Start daemon with specific services: --service userservice
• Collision Detection - Clear errors when command names conflict in hoisted services

Developer Experience

• CLI Annotations - Customize command names, flags, descriptions via proto options
• Type-Safe Options API - Functional options pattern for configuration
• Built on urfave/cli v3 - Modern, well-tested CLI framework

Quick Start

Installation

Add to buf.gen.yaml:

version: v2
plugins:
  - local: ["go", "run", "google.golang.org/protobuf/cmd/protoc-gen-go"]
    out: .
    opt: [paths=source_relative]
  - local: ["go", "run", "google.golang.org/grpc/cmd/protoc-gen-go-grpc"]
    out: .
    opt: [paths=source_relative]
  - local: ["go", "run", "github.com/drewfead/proto-cli/cmd/gen"]
    out: .
    opt: [paths=source_relative]

Basic Example

1. Define your service (example.proto):

import "internal/clipb/cli.proto";

service UserService {
  option (cli.service) = {
    name: "user-service"
    description: "Manage users"
  };

  rpc GetUser(GetUserRequest) returns (UserResponse) {
    option (cli.command) = {
      name: "get"
      description: "Retrieve a user by ID"
    };
  }
}

message GetUserRequest {
  int64 id = 1 [(cli.flag) = {name: "id", usage: "User ID"}];
  optional string fields = 2 [(cli.flag) = {name: "fields", usage: "Fields to return"}];
}

2. Generate code:

buf generate

3. Build your CLI (main.go):

ctx := context.Background()

// Create service implementation
userServiceCLI := simple.UserServiceCommand(ctx, &userService{},
    protocli.WithOutputFormats(protocli.JSON(), protocli.YAML()),
)

// Create root command
rootCmd, err := protocli.RootCommand("usercli",
    protocli.Service(userServiceCLI),
    protocli.WithEnvPrefix("USERCLI"),
)

rootCmd.Run(ctx, os.Args)

4. Use your CLI:

# Direct call (in-process)
./usercli user-service get --id 1

# Start gRPC server
./usercli daemonize --port 50051

# Remote call
./usercli user-service get --id 1 --remote localhost:50051

Examples

Simple Example

Basic CRUD operations with configuration loading, custom deserializers, and multi-service support.

Highlights:

• Configuration from YAML files and environment variables
• Optional proto3 fields with explicit presence
• Custom timestamp deserializers
• Nested configuration messages
• Multi-service CLI (UserService + AdminService)

Try it:

make build/example
./bin/usercli user-service get --id 1 --format json
./bin/usercli daemonize --port 50051

Streaming Example

Server-side streaming RPCs with line-delimited output formats.

Highlights:

• Server streaming RPC support
• NDJSON output for JSON format
• Offset and filtering with optional fields
• Works with Unix tools (jq, grep, wc)

Try it:

go build -o bin/streamcli ./examples/streaming/streamcli
./bin/streamcli streaming-service list-items --category books --format json | jq .

Flat Command Structure

Single-service CLIs with commands at the root level using protocli.Hoisted().

Comparison:

• Nested: ./usercli user-service get --id 1
• Flat: ./usercli-flat get --id 1

Usage:

rootCmd, err := protocli.RootCommand("usercli-flat",
    protocli.Service(userServiceCLI, protocli.Hoisted()),
)

See usercli_flat/README.md for details.

Key Features

Configuration Loading

Define configuration in your proto file using the service_config annotation:

// Define your configuration message
message UserServiceConfig {
  string database_url = 1 [(cli.flag) = {
    name: "db-url"
    usage: "PostgreSQL connection URL"
  }];
  int64 max_connections = 2 [(cli.flag) = {
    name: "max-conns"
    usage: "Maximum database connections"
  }];
}

// Attach config to your service
service UserService {
  option (cli.service_config) = {
    config_message: "UserServiceConfig"
  };

  rpc GetUser(GetUserRequest) returns (UserResponse);
}

Implement a factory function that receives the config:

func newUserService(config *simple.UserServiceConfig) simple.UserServiceServer {
    log.Printf("DB URL: %s, Max Conns: %d", config.DatabaseUrl, config.MaxConnections)
    return &userService{dbURL: config.DatabaseUrl}
}

// Register the factory
rootCmd := protocli.RootCommand("usercli",
    protocli.Service(userServiceCLI),
    protocli.WithConfigFactory("userservice", newUserService),
)

Load configuration from YAML files:

# usercli.yaml
services:
  userservice:
    database-url: postgresql://localhost:5432/users
    max-connections: 25

Override with environment variables:

USERCLI_SERVICES_USERSERVICE_DATABASE_URL=postgresql://prod/db ./usercli daemonize

Debugging Configuration Issues

Enable debug logging to see which config files are loaded and how values are merged:

# Use debug verbosity to see config loading details
./usercli daemonize --verbosity=debug

# Output shows:
# - Which config files were found/missing
# - Environment variables applied
# - Final merged configuration

Programmatically inspect configuration loading:

loader := protocli.NewConfigLoader(
    protocli.DaemonMode,
    protocli.FileConfig("./config.yaml"),
    protocli.EnvPrefix("MYAPP"),
    protocli.DebugMode(true),  // Enable debug tracking
)

config := &myapp.ServiceConfig{}
err := loader.LoadServiceConfig(nil, "myservice", config)

// Get detailed debug information
debug := loader.DebugInfo()
fmt.Printf("Paths checked: %v\n", debug.PathsChecked)
fmt.Printf("Files loaded: %v\n", debug.FilesLoaded)
fmt.Printf("Files failed: %v\n", debug.FilesFailed)
fmt.Printf("Env vars applied: %v\n", debug.EnvVarsApplied)
fmt.Printf("Final config: %+v\n", debug.FinalConfig)

Common Issues:

1. Config file not found: Check debug.PathsChecked to see where the CLI looked for config files
2. Values not applied: Check debug.EnvVarsApplied to verify environment variable names (they must match the prefix + field path)
3. Wrong precedence: Remember: CLI flags > environment variables > config files
4. Field naming: Proto fields use kebab-case in YAML (e.g., database_url → database-url)

See config_debug_test.go and nested_config_test.go for more examples.

Custom Flag Deserializers

Transform CLI flags into complex proto messages:

protocli.WithFlagDeserializer("google.protobuf.Timestamp",
    func(ctx context.Context, flags protocli.FlagContainer) (proto.Message, error) {
        t, err := time.Parse(time.RFC3339, flags.String())
        if err != nil {
            return nil, err
        }
        return timestamppb.New(t), nil
    },
)

See timestamp_deserializer_test.go.

Template-Based Output Formats

Create custom output formats using Go text templates without writing format code:

// Define templates for each message type
templates := map[string]string{
    "example.UserResponse": `User: {{.user.name}} (ID: {{.user.id}})
Email: {{.user.email}}
{{if .user.address}}Address: {{.user.address.city}}, {{.user.address.state}}{{end}}`,

    "example.CreateUserRequest": `Creating user: {{.name}} <{{.email}}>`,
}

// Create the format
userFormat, err := protocli.TemplateFormat("user-detail", templates)

// Use in CLI
userServiceCLI := simple.UserServiceCommand(ctx, newUserService,
    protocli.WithOutputFormats(userFormat, protocli.JSON()),
)

With Custom Template Functions:

funcMap := template.FuncMap{
    "upper": strings.ToUpper,
    "date": func(ts string) string {
        // Custom date formatting
        return formattedDate
    },
}

format, err := protocli.TemplateFormat("custom", templates, funcMap)

Template Features:

• Access all message fields as {{.fieldName}}
• Conditionals: {{if .field}}...{{end}}
• Loops: {{range .list}}...{{end}}
• Custom functions via template.FuncMap
• Nested field access: {{.user.address.city}}
• Format any message type by fully qualified name

Common Use Cases:

• Table formats: Create ASCII tables with printf for alignment
• Compact formats: One-line summaries like {{.name}} <{{.email}}>
• CSV/TSV: {{.id}},{{.name}},{{.email}}
• Custom business formats: Match your organization's output standards

See template_format_test.go for comprehensive examples.

Lifecycle Hooks

Add hooks for logging, authentication, metrics:

protocli.RootCommand("usercli",
    protocli.Service(userServiceCLI),
    protocli.BeforeCommand(func(ctx context.Context, cmd *cli.Command) error {
        log.Printf("Executing: %s", cmd.Name)
        return nil
    }),
    protocli.OnDaemonStartup(func(ctx context.Context, server *grpc.Server, mux *runtime.ServeMux) error {
        // Register additional services, configure server
        return nil
    }),
    protocli.OnDaemonReady(func(ctx context.Context) {
        log.Println("Server is ready")
    }),
    protocli.OnDaemonShutdown(func(ctx context.Context) {
        log.Println("Shutting down gracefully")
    }),
)

See daemon_lifecycle_test.go for complete examples.

Help Text Customization

Proto-CLI follows urfave/cli v3 best practices for help text. Customize help at multiple levels:

Proto Annotations:

Use proto annotations to define help text fields following urfave/cli v3 conventions:

service UserService {
  option (cli.service) = {
    name: "user-service",
    description: "User management commands",  // Short one-liner
    long_description: "Detailed explanation of the service...",  // Multi-paragraph
    usage_text: "user-service [command] [options]",  // Custom USAGE line
    args_usage: "[filter-expression]"  // Argument description
  };

  rpc GetUser(GetUserRequest) returns (UserResponse) {
    option (cli.command) = {
      name: "get",
      description: "Retrieve a user by ID",  // Short (shown in lists)
      long_description: "Fetch detailed user information...\n\nExamples:\n  usercli get --id 123",
      usage_text: "get --id <user-id> [options]",  // Override auto-generated USAGE
      args_usage: "<user-id>"  // Describe positional args
    };
  }
}

Help Field Guidelines (urfave/cli v3):

• description: Short one-liner for command lists (e.g., "retrieve a user by ID")
• long_description: Detailed explanation with examples and context
• usage_text: Override auto-generated USAGE line format
• args_usage: Describe expected arguments

Programmatic Customization:

// Method 1: Custom root command template
rootCmd, _ := protocli.RootCommand("myapp",
    protocli.Service(userServiceCLI),
    protocli.WithRootCommandHelpTemplate(`
NAME:
   {{.Name}} - {{.Usage}}

USAGE:
   {{.HelpName}} {{if .VisibleFlags}}[options]{{end}} command

VERSION:
   {{.Version}}

WEBSITE:
   https://example.com
`),
)

// Method 2: Full control with HelpCustomization
protocli.WithHelpCustomization(&protocli.HelpCustomization{
    RootCommandHelpTemplate: myTemplate,
    CommandHelpTemplate: myCommandTemplate,
    SubcommandHelpTemplate: mySubcommandTemplate,
})

// Method 3: Modify the returned root command
rootCmd, _ := protocli.RootCommand("myapp", protocli.Service(userServiceCLI))
rootCmd.Version = "1.0.0"
rootCmd.Copyright = "(c) 2026 MyCompany"
rootCmd.Authors = []any{"John Doe <john@example.com>"}

Best Practices:

• Keep description concise (one line) for readability in command lists
• Use long_description for detailed explanations, examples, and context
• Follow the urfave/cli v3 help conventions
• Include examples in long_description to aid discovery

Streaming RPCs

Server streaming RPCs output line-delimited messages:

# JSON format produces NDJSON (one JSON object per line)
./streamcli streaming-service list-items --format json
{"item":{"id":"1","name":"Item 1"}}
{"item":{"id":"2","name":"Item 2"}}

# Works with jq and other Unix tools
./streamcli streaming-service list-items --format json | jq 'select(.item.id > "1")'

See streaming example for details.

Optional Fields

Full support for proto3 optional fields with explicit presence:

message CreateUserRequest {
  string name = 1;  // Required
  optional string nickname = 2;  // Optional with presence tracking
  optional int32 age = 3;  // Only set if flag provided
}

Only sets the field if the flag is provided:

./usercli user-service create --name "Alice"  # nickname and age unset
./usercli user-service create --name "Alice" --nickname "ace"  # nickname set

gRPC Interceptors

Add interceptors for cross-cutting concerns:

protocli.WithUnaryInterceptor(func(ctx context.Context, req any, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (any, error) {
    start := time.Now()
    resp, err := handler(ctx, req)
    log.Printf("%s took %v", info.FullMethod, time.Since(start))
    return resp, err
}),
protocli.WithStreamInterceptor(streamLoggingInterceptor),

Selective Service Enable

Start daemon with only specific services:

# Start all services
./usercli daemonize --port 50051

# Start only userservice and productservice
./usercli daemonize --port 50051 --service userservice --service productservice

CLI Annotations

Customize generated CLIs using proto options from internal/clipb/cli.proto:

service UserService {
  option (cli.service) = {
    name: "users"  // Command name (default: snake_case service name)
    description: "User management commands"
  };

  rpc GetUser(GetUserRequest) returns (UserResponse) {
    option (cli.command) = {
      name: "get"  // Subcommand name
      description: "Retrieve user by ID"
    };
  }
}

message GetUserRequest {
  int64 id = 1 [(cli.flag) = {
    name: "id"
    shorthand: "i"
    usage: "User ID to retrieve"
  }];
}

Development

Prerequisites

• Go 1.23+
• Buf

Building

# Generate code
make generate

# Run tests
make test

# Run linter
make lint

# Build examples
make build/example

Project Structure

proto-cli/
├── cmd/gen/          # Code generator (protoc plugin)
├── examples/
│   ├── simple/       # Basic CRUD example
│   │   ├── usercli/      # Multi-service CLI
│   │   └── usercli_flat/ # Flat command structure
│   └── streaming/    # Server streaming example
├── internal/clipb/   # CLI annotation proto definitions
├── root.go           # Root command implementation
├── options.go        # Configuration options
├── config.go         # Configuration loading
└── formats.go        # Output formatters

Contributing

Contributions welcome! Please:

1. Add tests for new features
2. Run make lint before submitting
3. Update documentation

License

MIT License

Acknowledgments

• Built on urfave/cli v3
• Code generation via jennifer
• Proto tooling via Buf