---
title: Library Modules
description: Experimental cross-crate Slint library modules.
---

A Slint *library module* lets one Rust crate publish a set of `.slint` components and another crate import them through Cargo's dependency system.
The consumer writes `import { Foo } from "@libname";` and Cargo's build metadata tells the Slint compiler where to find the library source.

> **Note**: Library modules are experimental.
> The publishing side requires the `experimental-module-builds` feature of `slint-build`, and the consumer side requires the `experimental-library-module` feature of the Slint compiler.
> Tracking issue: [slint-ui/slint#154](https://github.com/slint-ui/slint/issues/154).

## Publishing a library

A crate that provides a library compiles its `.slint` entry point in its `build.rs` and marks it as a library.
This causes Cargo to emit `DEP_*` environment variables that downstream crates can read.

```rust
// build.rs of the publishing crate
fn main() {
    let config = slint_build::CompilerConfiguration::new()
        .as_library("mywidgets");
    slint_build::compile_with_config("ui/lib.slint", config).unwrap();
}
```

The crate's `Cargo.toml` must declare `links = "mywidgets"` so that Cargo forwards the metadata to dependent crates.

```toml
[package]
name = "mywidgets"
links = "mywidgets"
```

## Consuming a library

A crate that depends on the publishing crate imports its components with the `@` prefix followed by the library name:

```slint no-test
import { FancyButton } from "@mywidgets";

export component App inherits Window {
    FancyButton { text: "Click me"; }
}
```

No extra build.rs configuration is needed on the consumer side: the Slint compiler discovers the library through the `DEP_MYWIDGETS_SLINT_LIBRARY_*` environment variables that Cargo forwards automatically for `links` dependencies.

## Environment variables

When the publishing crate uses `as_library("name")`, its build script emits the following metadata, which Cargo exposes to dependents as `DEP_NAME_*`:

| Variable                     | Meaning                                       |
| ---------------------------- | --------------------------------------------- |
| `SLINT_LIBRARY_NAME`         | The library name used in the `@name` import.  |
| `SLINT_LIBRARY_SOURCE`       | Absolute path to the library's entry `.slint` file. |
| `SLINT_LIBRARY_PACKAGE`      | The publishing crate's package name.          |
| `SLINT_LIBRARY_MODULE`       | Optional Rust module path where the generated code lives. |

Ad-hoc local libraries that do not need to travel across crates can still be registered directly with `slint_build::CompilerConfiguration::with_library_paths`.
That API is stable and does not require the experimental feature.
