# effect

> The missing standard library for TypeScript, for writing production-grade software.

Latest version **3.22.2** (published 2026-09-09) · MIT license · 0 weekly downloads

## Install

```sh
npm install effect
pnpm add effect
yarn add effect
bun add effect
```

## Health

**Score 75/100 (B)** — status: active.

Positive: has types; esm support; no vulnerabilities; has provenance; recently updated; high maintenance score; popular repo.

Warnings: low downloads; large bundle.

## Facts

| | |
|---|---|
| Version | 3.22.2 |
| Published | 2026-09-09 |
| First published | 2022-11-25 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | ESM + CommonJS |
| Dependencies | 2 |
| Unpacked size | 25.9 MB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| Provenance | attested (GitHub Actions) |
| GitHub stars | 16025 |
| Maintainers | michael.arnaldi, effect-bot |

## Links

- npm: https://www.npmjs.com/package/effect
- Repository: https://github.com/Effect-TS/effect
- Homepage: https://effect.website
- Issues: https://github.com/Effect-TS/effect/issues
- npm.io page: https://npm.io/package/effect

## Dependencies (2)

- [fast-check](https://npm.io/package/fast-check.md) ^3.23.1
- [@standard-schema/spec](https://npm.io/package/@standard-schema/spec.md) ^1.0.0

## Recent versions

- 3.22.2 (latest) — 2026-09-09
- 4.0.0-rc.115 (rc) — 2026-09-11
- 4.0.0-beta.107 (beta) — 2026-08-10
- 0.0.0-snapshot-6ebc752baf28354006ca2a0ae783a5bccf5de9ad (snapshot) — 2024-07-15
- 4.0.0-rc.114 — 2026-09-11
- 4.0.0-rc.113 — 2026-09-10
- 4.0.0-rc.112 — 2026-08-25
- 4.0.0-rc.111 — 2026-08-20
- 4.0.0-rc.110 — 2026-08-17
- 4.0.0-rc.109 — 2026-08-14
- 4.0.0-rc.108 — 2026-08-12
- 4.0.0-beta.106 — 2026-08-08
- 4.0.0-beta.105 — 2026-08-07
- 4.0.0-beta.104 — 2026-08-06
- 4.0.0-beta.103 — 2026-08-04
- … 466 more at https://npm.io/package/effect/versions

## README

# `effect` Core Package

The `effect` package is the heart of the Effect framework, providing robust primitives for managing side effects, ensuring type safety, and supporting concurrency in your TypeScript applications.

## Requirements

- **TypeScript 5.4 or Newer:**
  Ensure you are using a compatible TypeScript version.

- **Strict Type-Checking:**
  The `strict` flag must be enabled in your `tsconfig.json`. For example:

  ```json
  {
    "compilerOptions": {
      "strict": true
      // ...other options
    }
  }
  ```

## Installation

Install the core package using your preferred package manager. For example, with npm:

```bash
npm install effect
```

## Documentation

- **Website:**
  For detailed information and usage examples, visit the [Effect website](https://www.effect.website/).

- **API Reference:**
  For a complete API reference of the core package `effect`, see the [Effect API documentation](https://effect-ts.github.io/effect/).

## Overview of Effect Modules

The `effect` package provides a collection of modules designed for functional programming in TypeScript. Below is a brief overview of the core modules:

| Module   | Description                                                                                                                |
| -------- | -------------------------------------------------------------------------------------------------------------------------- |
| Effect   | The core abstraction for managing side effects, concurrency, and error handling in a structured way.                       |
| Context  | A lightweight dependency injection mechanism that enables passing services through computations without direct references. |
| Layer    | A system for managing dependencies, allowing for modular and composable resource allocation.                               |
| Fiber    | Lightweight virtual threads with resource-safe cancellation capabilities, enabling many features in Effect.                |
| Stream   | A powerful abstraction for handling asynchronous, event-driven data processing.                                            |
| Schedule | A module for defining retry and repeat policies with composable schedules.                                                 |
| Scope    | Manages the lifecycle of resources, ensuring proper acquisition and release.                                               |
| Schema   | A powerful library for defining, validating, and transforming structured data with type-safe encoding and decoding.        |

For a comparison between `effect/Schema` and `zod`, see [Schema vs Zod](https://github.com/Effect-TS/effect/tree/main/packages/effect/schema-vs-zod.md).

---
_Source: https://npm.io/package/effect · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._