---
title: Built-in Packages
description: Versioned toolchains, commands, and task environment helpers provided by xx.
---

# Built-in Packages

Built-in packages provide dependencies and functions to build and run project tasks. Load symbols from a package with Starlark's `load` function.

## Go

[`go`](packages/go/go.md), [`go_binary`](packages/go/go_binary.md), [`go_install`](packages/go/go_install.md), [`go_run`](packages/go/go_run.md), [`go_test`](packages/go/go_test.md)

## Node.js

[`nodejs`](packages/nodejs/nodejs.md), [`npm_install`](packages/nodejs/npm_install.md), [`npm_run`](packages/nodejs/npm_run.md), [`npx_run`](packages/nodejs/npx_run.md)

## OS

[`env_append`](packages/os/env_append.md), [`env_get`](packages/os/env_get.md), [`env_prepend`](packages/os/env_prepend.md), [`env_set`](packages/os/env_set.md), [`env_unset`](packages/os/env_unset.md), [`run`](packages/os/run.md)

## Zig

[`zig`](packages/zig/zig.md), [`zig_cc`](packages/zig/zig_cc.md)

Package names include a version. Tool packages use an exact tool version, while the OS package uses API version `1`:

```python
load("@go@1.26.5", "go_test")
load("@os@1", "env_set")
```

<!--
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URL: https://withxx.dev/index.md
Title: xx
Description: Practical, reproducible builds without build-system ceremony

URL: https://withxx.dev/examples/commands.md
Title: Command Examples
Description: General command, environment, and entrypoint patterns.

URL: https://withxx.dev/examples/go.md
Title: Go Examples
Description: Common Go build patterns with managed SDKs.

URL: https://withxx.dev/examples/nodejs.md
Title: Node.js Examples
Description: Common Node.js task patterns with a managed distribution.

URL: https://withxx.dev/examples/zig.md
Title: Zig Examples
Description: Direct Zig commands and Go CGO builds with a managed Zig distribution.

URL: https://withxx.dev/load.md
Title: Loading Files
Description: Split xx configuration into local Starlark modules.

URL: https://withxx.dev/packages/go/go.md
Title: go
Description: Activate a managed Go SDK for dependent tasks.

URL: https://withxx.dev/packages/go/go_binary.md
Title: go_binary
Description: Build a Go command with a managed SDK.

URL: https://withxx.dev/packages/go/go_install.md
Title: go_install
Description: Install a versioned Go command for dependent tasks.

URL: https://withxx.dev/packages/go/go_run.md
Title: go_run
Description: Run a versioned Go command with a managed SDK.

URL: https://withxx.dev/packages/go/go_test.md
Title: go_test
Description: Test Go packages with a managed SDK.

URL: https://withxx.dev/packages/nodejs/nodejs.md
Title: nodejs
Description: Activate managed Node.js for dependent tasks.

URL: https://withxx.dev/packages/nodejs/npm_install.md
Title: npm_install
Description: Install project dependencies with managed npm.

URL: https://withxx.dev/packages/nodejs/npm_run.md
Title: npm_run
Description: Run a project package script with managed npm.

URL: https://withxx.dev/packages/nodejs/npx_run.md
Title: npx_run
Description: Run a versioned npm package command with managed npx.

URL: https://withxx.dev/packages/os/env_append.md
Title: env_append
Description: Append an item to a list-like environment variable.

URL: https://withxx.dev/packages/os/env_get.md
Title: env_get
Description: Read a value from a task environment while evaluating Starlark.

URL: https://withxx.dev/packages/os/env_prepend.md
Title: env_prepend
Description: Prepend an item to a list-like environment variable.

URL: https://withxx.dev/packages/os/env_set.md
Title: env_set
Description: Set an environment variable for dependent tasks.

URL: https://withxx.dev/packages/os/env_unset.md
Title: env_unset
Description: Remove an environment variable from dependent tasks.

URL: https://withxx.dev/packages/os/run.md
Title: run
Description: Run a command from the project root.

URL: https://withxx.dev/packages/zig/zig.md
Title: zig
Description: Activate managed Zig for dependent tasks.

URL: https://withxx.dev/packages/zig/zig_cc.md
Title: zig_cc
Description: Configure managed Zig as a C and C++ compiler.

URL: https://withxx.dev/packages.md
Title: Built-in Packages
Description: Versioned toolchains, commands, and task environment helpers provided by xx.
-->