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Getting Started with Klar

Install

# macOS / Linux
curl -fsSL https://klar.dev/install | sh

# Verify installation
klar --version

Create a Project

klar new my-app
cd my-app

This creates:

my-app/
├── klar.toml          # Project manifest
├── src/
│   └── main.klar      # Entry point
└── test/
    └── main_test.klar  # Tests

Hello World

// src/main.klar
fn main() {
    println("Hello, world!")
}

klar run
# Output: Hello, world!

Your First API

klar new my-api --template api
cd my-api

// src/main.klar
use std.http.{Router, Request, Response, serve}

@schema
struct Greeting {
    message: String
    timestamp: DateTime
}

fn main() ! ServerError {
    let router = Router.new()
        |> Router.get("/hello/{name}", hello)
    serve(router, port: 3000)?
}

fn hello(req: Request) -> Response ! AppError {
    let name = req.param("name")
    let greeting = Greeting {
        message: "Hello, {name}!",
        timestamp: time.now(),
    }
    Response.json(greeting)
}

klar run
# Server running on :3000

curl localhost:3000/hello/world
# {"message":"Hello, world!","timestamp":"2026-03-30T12:00:00Z"}

AI Setup

To enable AI code generation for Klar, add the language spec to your AI tool:

Claude Code / Claude Projects

Copy LANGUAGE_SPEC.md (shipped with the compiler at ~/.klar/LANGUAGE_SPEC.md) into your Claude Project knowledge.

Cursor

Copy to .cursorrules in your project root:

cp ~/.klar/LANGUAGE_SPEC.md .cursorrules

VS Code

Install the Klar extension from the VS Code Marketplace. It includes the LSP for real-time diagnostics, completions, and formatting.

Toolchain Commands

Command Description
klar new <name> Create a new project
klar build Compile the project
klar run Build and execute
klar test Run all tests
klar fmt Format source code
klar lint Run static analysis
klar add <pkg> Add a dependency
klar check Type-check without building
klar doc --open Generate and view docs
klar repl Interactive REPL

Next Steps