> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/Effect-TS/tsgo/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

> Effect Language Service (tsgo) brings Effect-specific diagnostics, quick fixes, refactors, and completions to the TypeScript-Go high-performance language server.

<Warning>
  `@effect/tsgo` is currently in **Alpha**. Expect breaking changes between releases and some missing features compared to the previous TypeScript-based version. Some features are on hold pending upstream TypeScript-Go progress.
</Warning>

## What is Effect Language Service (tsgo)?

`@effect/tsgo` is a **superset of [TypeScript-Go](https://github.com/nicolo-ribaudo/TypeScript-Go)** — the high-performance, Go-based rewrite of the TypeScript compiler — augmented with the full Effect Language Service. It ships as a single binary (`effect-tsgo`) that acts as your editor's TypeScript language server and adds Effect-specific intelligence on top.

The project targets **Effect V4** (codename: "smol") as its primary target, with Effect V3 also supported for most diagnostics and refactors.

## Architecture

`effect-tsgo` is composed of two layers:

1. **TypeScript-Go core** — a pinned, patched build of the upstream `tsgo` binary. This provides the standard TypeScript language server experience at Go-native speed: completions, go-to-definition, hover, rename, and all other baseline LSP features.
2. **Effect Language Service layer** — built on top of the TypeScript-Go core, this layer adds Effect-specific diagnostics, quick fixes, refactors, smart completions, and layer graph visualization.

Your editor talks to `effect-tsgo` over the standard TypeScript server protocol (tsserver), so it is compatible with any editor that supports TypeScript via tsserver.

<Info>
  Use `effect-tsgo` **instead of** `tsgo`, not alongside it. Running both in parallel produces duplicate diagnostics and degrades editor performance.
</Info>

## Relationship to TypeScript-Go

Each release of `@effect/tsgo` is built against a specific, pinned upstream `tsgo` commit. The Effect layer is applied as a minimal patch set on top. This means:

* You get all standard TypeScript-Go functionality plus Effect-specific features from a single binary.
* You do not need to track upstream `tsgo` releases separately — `effect-tsgo` is the single binary to manage.
* When upstream `tsgo` releases new features or fixes, `effect-tsgo` adopts them in a subsequent release after validating compatibility with the Effect diagnostics layer.

## What problems does it solve?

Writing correct Effect-TS code involves patterns — generators, error channels, context requirements, service layers — that TypeScript alone cannot enforce. `@effect/tsgo` gives you immediate, in-editor feedback for the most common sources of bugs and confusion:

* **Unhandled errors and requirements**: Surfaces unhandled error types and context requirements as compile errors, not silent runtime failures.
* **Floating effects**: Catches `Effect` values that are neither yielded nor assigned, which silently go unexecuted.
* **Generator mistakes**: Detects `yield` without `*`, missing `return yield*`, and nested `Effect<Effect<...>>` caused by returning inside a generator.
* **Anti-patterns**: Warns against patterns like chained `.provide()` calls, `Effect.run*` inside generators, and IIFE usage of `Effect.fn`.
* **Style and idiom**: Suggests idiomatic rewrites — `Effect.asVoid`, `Effect.void`, `Effect.fn`, opaque schemas, pipe style — with one-keystroke quick fixes.
* **V4 migration**: Detects APIs removed or renamed between Effect V3 and V4.

## Key features

<CardGroup cols={2}>
  <Card title="50+ diagnostics" icon="triangle-exclamation" href="/diagnostics/overview">
    Correctness, anti-pattern, Effect-native, and style diagnostics covering the most common Effect-TS pitfalls. Configurable severities.
  </Card>

  <Card title="Quick fixes" icon="wand-magic-sparkles" href="/diagnostics/overview">
    One-keystroke code actions to resolve many diagnostics automatically — fix missing `yield*`, remove redundant wrappers, rewrite to idiomatic APIs.
  </Card>

  <Card title="Refactors" icon="rotate" href="/features/refactors">
    Convert async/await to Effect generators or `Effect.fn`, compose layers automatically, generate schemas from types, toggle pipe style, and more.
  </Card>

  <Card title="Smart completions" icon="list-check" href="/features/completions">
    Context-aware snippets for `Effect.gen`, Schema classes, Service/Tag constructors, and diagnostic/codegen comment directives.
  </Card>

  <Card title="Layer graph" icon="diagram-project" href="/features/layer-graph">
    Hover over any `Layer` value to see a live Mermaid dependency diagram showing the full service graph.
  </Card>

  <Card title="V3 & V4 support" icon="code-branch">
    Works with both Effect V3 and V4. V4-only rules are skipped automatically on V3 projects.
  </Card>
</CardGroup>

## Supported Effect versions

| Feature area              | Effect V3 | Effect V4 |
| ------------------------- | --------- | --------- |
| Correctness diagnostics   | Most      | All       |
| Anti-pattern diagnostics  | All       | All       |
| Effect-native diagnostics | All       | All       |
| Style diagnostics         | All       | All       |
| Refactors                 | All       | All       |
| Completions               | All       | Most      |

## Get started

<CardGroup cols={2}>
  <Card title="Quickstart" icon="rocket" href="/quickstart">
    Install `@effect/tsgo` in your project using the interactive setup wizard.
  </Card>

  <Card title="Editor setup" icon="code" href="/editor-setup">
    Configure VS Code, Neovim, or any tsserver-compatible editor.
  </Card>
</CardGroup>