lemmy-ui is the official web app for Lemmy — the federated link aggregator and forum of the Fediverse — and it is built for the people who run and use Lemmy servers rather than for anyone seeking a centrally hosted social network.

What it is

lemmy-ui is the front-end web application for Lemmy, a self-hostable, decentralized link aggregator and discussion forum. It lives in the LemmyNet organisation alongside the backend it talks to, and it is written in CSS and built on the Inferno framework. A Lemmy instance is a server that hosts forums, called communities, where people subscribe to topics, post links and discussions, then vote and comment on them. Because Lemmy servers are federated in the manner of email, a user registered on one server can subscribe to communities on any other server and hold discussions with users registered elsewhere, all within a single connected universe.

The concrete problem it solves is the presentation layer of that federation. Lemmy splits into a backend service and this web interface, and lemmy-ui is the part that renders the site in the browser and connects to the backend. For an operator, that means the interface is a separately deployable component that can be pointed at any Lemmy backend, configured independently, and themed with custom CSS. It replaces the need for a hosted, advertising-driven link aggregator under corporate control: instead of a single company mediating every community, each Lemmy server sets its own moderation policy and appoints site-wide admins and community moderators to keep out trolls.

Key capabilities

• Runs as an isomorphic Node server, configured with LEMMY_UI_HOST (default 0.0.0.0:1234) for the IP and port it binds.
• Connects to a Lemmy backend through LEMMY_UI_BACKEND (default localhost:8536), with a separate LEMMY_UI_BACKEND_INTERNAL for server-to-server requests and LEMMY_UI_FRONTEND for the browser-facing base URL.
• Switches base URL protocol via the LEMMY_UI_HTTPS boolean, defaulting to false.
• Loads additional CSS themes from LEMMY_UI_EXTRA_THEMES_FOLDER, defaulting to ./extra_themes.
• Supports independent frontend development with LEMMY_UI_BACKEND=https://voyager.lemmy.ml pnpm dev, serving the app on http://localhost:1234.
• Publishes community translations through the Weblate instance at weblate.join-lemmy.org.
• Ships as a Docker image, dessalines/lemmy-ui, and is distributed under AGPL-3.0.

Who uses it and how

• Lemmy server operators who self-host the front end alongside the backend to run their own instance.
• Instance administrators who set site-wide moderation policy and appoint community moderators for the communities they host.
• Frontend contributors who work against the public test instance at https://voyager.lemmy.ml or against a locally compiled Lemmy backend.
• Translators who contribute through the project's Weblate instance.
• Members of federated instances who subscribe to communities on other servers and hold discussions across server boundaries.

Getting started

Development requires pnpm; the README flow is git clone https://github.com/LemmyNet/lemmy-ui.git --recursive, then pnpm install, then LEMMY_UI_BACKEND=https://voyager.lemmy.ml pnpm dev, opening http://localhost:1234. The README also references the Docker image dessalines/lemmy-ui for deployment.

How it compares

The README places Lemmy alongside Reddit, Lobste.rs, and Hacker News as the sites whose experience it resembles: subscribe to forums, post links and discussions, vote, and comment. The difference it draws is architectural rather than cosmetic — Lemmy runs on servers anyone can operate, and those servers federate, so the equivalent of a subreddit can live on any instance instead of inside one company's platform. Within this registry, lemmy-ui is the official front end for that model, not an alternative client for the sites named.

When to use it — and when not to

Choose lemmy-ui if there is already a Lemmy backend to point at, because the interface does nothing on its own and expects a backend at LEMMY_UI_BACKEND, defaulting to localhost:8536. A self-hoster must operate both the Node server for the interface and the Lemmy backend behind it, including whatever the backend requires. It is a poor fit for anyone wanting an all-in-one hosted product, or unwilling to carry the obligations of an AGPL-3.0 codebase. The README excerpt is developer-oriented and its configuration table is truncated, so prospective operators should read the full documentation at join-lemmy.org rather than relying on this page alone.

git clone https://github.com/LemmyNet/lemmy-ui.git --recursive
cd lemmy-ui
pnpm install
LEMMY_UI_BACKEND=https://voyager.lemmy.ml pnpm dev