Quickstart

Get from zero to a running Forst program with validated input.

1. Install the compiler

Install via your package manager:

npm
bun
pnpm
Native binary

npm install -D @forst/cli
npx forst version

The wrapper downloads the matching native binary on first use. See Installation for CI and offline setups.

bun add -d @forst/cli
bunx forst version

The wrapper downloads the matching native binary on first use. See Installation for CI and offline setups.

pnpm add -D @forst/cli
pnpm exec forst version

The wrapper downloads the matching native binary on first use. See Installation for CI and offline setups.

Download the latest release for your platform from GitHub Releases, add it to your PATH, then:

forst version

2. Create your first file

Create hello.ft:

3. Run it

Compile, build, and run the file:

npx forst run hello.ft

Forst transpiles to Go, builds, and runs the program. You should see Hello, World! on stdout.

4. Add validated input

Replace the body of hello.ft with a handler that only accepts well-formed orders. Constraints live on the type. Invalid calls fail at compile time and runtime checks are emitted automatically.

Forst
Generated Go

package main

type PlaceOrderInput = {
	stockKeepingUnit: String.Min(1).Max(64),
	quantity:         Int.Min(1).Max(99),
}

func placeOrder(in: PlaceOrderInput) {
	println("Order placed:", in.stockKeepingUnit, in.quantity)
}

func main() {
	placeOrder({
		stockKeepingUnit: "ITEM-1",
		quantity:         2,
	})
}

// forst build
package main

type PlaceOrderInput struct {
	stockKeepingUnit string
	quantity         int
}

func main() {
	placeOrder(PlaceOrderInput{
		stockKeepingUnit: "ITEM-1",
		quantity:         2,
	})
}

func placeOrder(in PlaceOrderInput) {
	println("Order placed:", in.stockKeepingUnit, in.quantity)
}

Run again:

npx forst run hello.ft

Try changing quantity to 0 or 100. The typechecker rejects out of range values before you ship.

5. Summary

Manual Go	Forst
Struct + manual `if len(sku) < 1` checks	Constraints on the type itself
Separate Zod/Yup schema for TS clients	`forst generate` emits matching `.d.ts`
Two sources of truth for API shapes	One `.ft` definition, Go + TS from the same tree

Next steps

Shapes and constraints

Structural typing and runtime validation.

Generate client types

Emit generated/types.d.ts for your frontend or BFF.

CLI reference

run, build, generate, dev, and more.

Go interop

Import Go packages and mix .ft with .go.

Overview

Getting started

Data validation

Behavior

Interop

Workflow

1. Install the compiler

2. Create your first file

3. Run it

4. Add validated input

5. Summary

Next steps

Shapes and constraints

Generate client types

CLI reference

Go interop

​1. Install the compiler

​2. Create your first file

​3. Run it

​4. Add validated input

​5. Summary

​Next steps

Shapes and constraints

Generate client types

CLI reference

Go interop

1. Install the compiler

2. Create your first file

3. Run it

4. Add validated input

5. Summary

Next steps