Installation

Effect ships as a single package, effect, that contains the entire core library — the Effect type, Schema, Stream, Layer, and much more. Installing that one package is all you need to start. This page walks you through creating a fresh, strict TypeScript project and running a first program.

Requirements:

• TypeScript 5.8 or newer (Effect v4 is developed and built against TypeScript 6.x — use the latest release for the best results)
• A runtime: Bun, Node.js 18+, or Deno

Caution

Effect relies on strict mode to give you accurate types for the error (E) and requirement (R) channels. Make sure "strict": true is set in your tsconfig.json — without it, inference will be wrong.

Create a project

1. Create a project directory and move into it:

   mkdir hello-effect
   cd hello-effect

2. Initialize the project and install TypeScript and Effect:

   Bun

   bun init -y
   bun add effect
   bun add -d typescript

   npm

   npm init -y
   npm install effect
   npm install --save-dev typescript tsx

   pnpm

   pnpm init
   pnpm add effect
   pnpm add -D typescript tsx

3. Generate a tsconfig.json and make sure strict mode is on:

   Bun

   bun init already creates a tsconfig.json with strict enabled. Verify it contains:

   {
     "compilerOptions": {
       "strict": true
     }
   }

   npm

   npx tsc --init

   Then open tsconfig.json and confirm:

   {
     "compilerOptions": {
       "strict": true
     }
   }

   pnpm

   pnpm tsc --init

   Then open tsconfig.json and confirm:

   {
     "compilerOptions": {
       "strict": true
     }
   }

Write a first program

Create a source file:

mkdir -p src
touch src/index.ts

Add the following to src/index.ts. The program is described as a value, then handed to a runtime to actually run:

src/index.ts

import { Console, Effect } from "effect"

// `Effect.gen` builds an effect in imperative style. Nothing runs yet — this is
// just a description of the work to be done.
const program = Effect.gen(function* () {
  yield* Console.log("Hello, Effect!")
})

// `Effect.runPromise` executes the program and returns a Promise. This is the
// boundary between the Effect world (descriptions) and the outside world.
Effect.runPromise(program)

Run it

Bun

bun run src/index.ts

npm

npx tsx src/index.ts

pnpm

pnpm tsx src/index.ts

You should see Hello, Effect! printed to the console. That confirms your project is set up correctly.

Tip

For a smoother developer experience — better diagnostics and inline error/type hints directly in your editor — install the Effect LSP plugin. It surfaces the E and R channels and catches common mistakes as you type.

Next steps

Now that everything runs, the Quickstart builds a small but realistic program with services, typed errors, and a Layer. To learn how the package is organized and how to reach the unstable modules (HTTP, CLI, RPC, and more), see Importing Effect.