# Installing effects

Download optional source packs, pin versions and present offline.

Source: https://legend.so/slides/effects/installation/

Legend Slides: Preview.

Choose an effect in the [gallery](https://legend.so/slides/effects/) and click **Install in Slides**. Slides shows the requested pack and version before installing it. **Open example in Slides** installs the required pack and opens a self-contained sample deck. These links require a Slides build with the `legend-slides` URL scheme registered. Public app downloads are still in preview.

## [Opening an existing deck](https://legend.so/slides/effects/installation/#opening-an-existing-deck)

When a deck needs effects that are not installed, the presenter offers **Install Required Effects**. The installer includes declared dependencies. Failed downloads can be retried without activating a partial pack or replacing a deck's versions.

A file named `talk.mdx.effects.lock.json` beside `talk.mdx` records exact versions and source checksums. Commit it with the deck. Multiple installed versions coexist; updating a pack for a new deck does not update existing lockfiles. Finish installing before presenting; compiling and playback make no network requests.

## [Source development and the CLI](https://legend.so/slides/effects/installation/#source-development-and-the-cli)

From a Legend Apps checkout:

```sh
bun scripts/compile-slides.ts /path/to/talk.mdx --install-effects
```

`LEGEND_SLIDES_EFFECTS_CATALOG` can point at a local docs server for development. `LEGEND_SLIDES_EFFECT_PACKS` changes the installation directory. The default cache is `~/Library/Application Support/Legend Slides/effects/`. Local source packs remain available for development without downloading; installed decks use their lockfile.

Packs share the native capabilities already in Slides. Installing source does not add another native runtime or require rebuilding the app.

To contribute an effect or release a pack, follow [Publishing effect packs](https://legend.so/slides/effects/publishing/).

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