---
url: https://wvlet.org/uni/index.md
description: >-
  Uni is the Scala 3 successor of Airframe: object wiring, logging,
  JSON/MessagePack, Rx, HTTP, RPC, MCP servers, and testing with minimal
  dependencies, on JVM, Scala.js, and Scala Native.
---

# Uni

## What is Uni?

**Uni is a Scala 3 library that gives you object wiring (Design), logging,
JSON/MessagePack, Rx, HTTP client/server, RPC, MCP servers, and testing from one
project, with minimal dependencies, and the same code runs on JVM, Scala.js, and
Scala Native.** It is the
Scala 3 successor of [Airframe](https://github.com/wvlet/airframe), for people
who build services, CLIs, and tools in Scala 3 and want one consistent set of
conventions across these concerns.

## Install

::: code-group

```scala [sbt]
libraryDependencies += "org.wvlet.uni" %% "uni" % "2026.1.39"

// Testing
libraryDependencies += "org.wvlet.uni" %% "uni-test" % "2026.1.39" % Test
testFrameworks += new TestFramework("wvlet.uni.test.Framework")

// Netty HTTP server (JVM only)
libraryDependencies += "org.wvlet.uni" %% "uni-netty" % "2026.1.39"
```

```scala [Scala CLI]
//> using dep org.wvlet.uni::uni:2026.1.39
```

:::

## Example: Design, logging, and JSON

```scala
import wvlet.uni.design.Design
import wvlet.uni.log.LogSupport
import wvlet.uni.weaver.Weaver

case class Greeting(name: String, message: String) derives Weaver

class Greeter extends LogSupport:
  def greet(name: String): String =
    info(s"Greeting ${name}")
    Weaver.toJson(Greeting(name, s"Hello, ${name}!"))

@main def hello =
  Design.newDesign.bindSingleton[Greeter].build[Greeter] { greeter =>
    println(greeter.greet("Uni")) // {"name":"Uni","message":"Hello, Uni!"}
  }
```

## Why one library?

* **Minimal dependencies.** On the JVM, `uni` depends only on the Scala 3
  standard library. Scala.js and Scala Native add only the platform shims they
  need, such as `java.time` support.
* **One version to upgrade.** Object wiring, logging, codecs, HTTP, and tests are
  released together, so they never disagree on transitive dependencies.
* **One codebase on three platforms.** The same code runs on the JVM, in Node.js or
  the browser, and as a Scala Native binary.
* **One set of conventions.** Case classes become JSON, RPC payloads, and MCP
  tool arguments through the same `Weaver` codecs.

Focused libraries and ecosystems such as sttp, circe, ZIO, and MacWire are good
choices,
and if they already serve you well there is no need to switch. Uni fits best
when you want these pieces from one place, especially when targeting Scala.js
or Scala Native.

## Used by Wvlet

[Wvlet](https://github.com/wvlet/wvlet), a flow-style query language and its
CLI and server, is built on `uni`, `uni-test`, and `uni-netty`.

## For AI agents

* [`llms.txt`](https://wvlet.org/uni/llms.txt) (page index) and
  [`llms-full.txt`](https://wvlet.org/uni/llms-full.txt) (all docs in one file)
* [Uni for AI Agents](/guide/for-ai-agents): canonical imports, an Airframe
  migration table, and common mistakes
* [Context7](https://context7.com/wvlet/uni)
* Claude Code plugin: `/plugin marketplace add wvlet/uni`, then
  `/plugin install uni@uni`

## Modules

| Module | Contents | Platforms |
|--------|----------|-----------|
| `uni` | Design, logging, JSON/MessagePack, Rx, HTTP client, Node.js/Native HTTP servers, RPC, MCP, [CLI utilities](/cli/), [Web UI](/dom/) (Scala.js) | JVM, Scala.js, Scala Native |
| `uni-netty` | Netty HTTP server, annotation router, HTTP RPC server | JVM |
| `uni-test` | UniTest framework | JVM, Scala.js, Scala Native |