cli-engine

cli-engine is a Rust library for building consistent, domain-oriented CLI applications. It provides shared framework pieces for command registration, authentication, authorization hooks, middleware, structured output, schemas, guides, search, command tree rendering, and HTTP transport.

Consumer CLIs bring their own binary entrypoint and domain modules. cli-engine owns the common execution pipeline so teams can add commands by copying a nearby command and filling in the domain-specific details.

Quick Start

use std::process::ExitCode;

use clap::Arg;
use cli_engine::{
    BuildInfo, Cli, CliConfig, CommandResult, CommandSpec, GroupSpec, Module, RuntimeCommandSpec,
    RuntimeGroupSpec,
};
use serde_json::json;

#[tokio::main]
async fn main() -> ExitCode {
    let list = RuntimeCommandSpec::new(
        CommandSpec::new("list", "List projects")
            .with_system("projects-api")
            .with_default_fields("id,name,status")
            .with_arg(Arg::new("team").long("team").required(true))
            .no_auth(true),
        async |_credential, args| {
            let team = args
                .get("team")
                .and_then(|value| value.as_str())
                .unwrap_or_default();

            Ok(CommandResult::new(json!([
                { "id": "project-1", "name": "Portal", "status": "active", "team": team }
            ])))
        },
    );

    let module = Module::new("Platform Systems", move |_context| {
        RuntimeGroupSpec::new(GroupSpec::new("project", "Manage projects"))
            .with_command(list.clone())
    });

    let cli = Cli::new(
        CliConfig::new("example", "Example cli-engine application", "example")
            .with_build(BuildInfo::new(env!("CARGO_PKG_VERSION")))
            .with_module(module),
    );

    cli.execute().await
}

Command paths are colon-separated, such as project:list, for policy, schema, audit, activity, and authorization metadata.

Guide Embedding

Guide markdown can be read from disk during development with parse_guides("guides"), or embedded in the consumer CLI binary with standard Rust compile-time embedding:

use cli_engine::Module;

let module = Module::new("Platform Systems", register).with_guides_from_markdown([
    ("guides/deploy.md", include_bytes!("../guides/deploy.md").as_slice()),
    ("guides/operate.md", include_bytes!("../guides/operate.md").as_slice()),
]);

For large guide directories, applications can use an embedding crate or a build.rs generated manifest that produces the same (path, bytes) pairs.

Output formats

Commands render as json, toon, or human. The default is context-aware: an interactive terminal gets human output, while pipes, files, CI, and most agents (anything where stdout is not a TTY) get json. The resolved format is chosen by this precedence (highest first):

1. An explicit flag on the invocation — --output <json|toon|human>, or the --json / --toon / --human shorthands.
2. The ${APP_ID}_OUTPUT environment variable (e.g. GODADDY_OUTPUT=json, GDX_OUTPUT=json). The name is derived from the app id (upper-cased, non-alphanumerics replaced with _). The value is case-insensitive; blank or unrecognized values are ignored and fall through to the TTY policy.
3. The TTY policy: human on an interactive terminal, json otherwise.

This keeps a human at a terminal from getting a wall of JSON while machine callers still get JSON automatically. An agent running in a PTY (which reads as interactive) can force machine output with either the env variable or an explicit flag. Streaming commands always emit newline-delimited JSON regardless of the resolved format.

Documentation

• Concepts
• Design
• Authentication and transport
• Basic example
• Agent instructions

Cargo Features

Verification

cargo fmt --all --check
cargo check --all-targets
cargo clippy --all-targets -- -D warnings
cargo test --all-targets
RUSTDOCFLAGS='-D warnings' cargo doc --no-deps
cargo test --doc