Show HN: hmr-serve, hot-loading web app for any folder (MIT)

HMR-serve, a new open-source tool by an unnamed developer, turns any folder into a hot-loading web app with instant updates via Vite's HMR, supporting Markdown, HTML, code, CSV, and images. Released under MIT license, it aims to simplify previewing files locally, including AI agent output, without a build step.

HMR-serve is inspired by npm run dev and by serve https://www.npmjs.com/package/serve . It turns any folder into a hot-loading web app, because sometimes it's nice to preview HTML, Markdown, images and other files in the browser. Point hmr-serve at any folder and review it live in the browser: a VSCode-style file tree on the left, a content pane on the right and instant updates as files change on disk , powered by Vite's real dev server and HMR https://vitejs.dev/guide/features.html hot-module-replacement client. 🔥 HMR Hot Module Replacement is the mechanism that pushes file changes into the browser over a WebSocket so the page updates without a full refresh. This project uses Vite's HMR https://vitejs.dev/guide/features.html hot-module-replacement rather than inventing its own. Tip:Helpful for reviewing AI agent output markdown/HTML docs as it iterates. npx hmr-serve ./some-folder → opens http://localhost:5183 with a live tree + content pane Or run it like serve without the nav, which serves a directory listing or index.html if present, plus rendered Markdown, CSV/TSV, all with HMR: npx hmr-serve ./some-folder --no-nav For a permanent setup, install globally and use the short hmr command: npm install -g hmr-serve hmr ./some-folder hmr ./some-folder --no-nav CLI: hmr dir Folder to serve default: current directory --port <port Port to listen on default: 5183 --open Open the browser on start --no-nav Like serve, without the tree UI Default nav mode shows a VS Code-style file tree and content pane. Supported types: Markdown rendered , HTML sandboxed iframe , code .css , .js , .ts , .json , … syntax-highlighted , text , CSV/TSV tables , images and video . A gear menu toggles which categories show in the tree, plus an Other files option. Choices are remembered per folder localStorage . --no-nav skips the tree UI: if the folder has index.html or index.htm , that is the root page; otherwise you get a directory listing. Markdown, CSV and TSV are still rendered to HTML, and edits hot-reload via Vite. No build step for your content. Runs in Vite dev-server mode only. The app shell a tiny Vue UI is Vite's root; your folder is mounted alongside it via middleware + server.fs.allow . Your files are the content — nothing is compiled. Live search index. Built at startup with MiniSearch https://github.com/lucaong/minisearch no native deps and kept current incrementally off file-watch events — no rebuild step. Plain HTTP + WebSocket, cross-browser. The browser only talks to the Node server over HTTP and Vite's HMR socket. No File System Access API, no Chromium-only APIs — works in Safari and Firefox. Extensible renderer registry. .md → markdown-it ; .html → sandboxed iframe; .css / .txt → server-side highlight.js ; .csv / .tsv → HTML tables styled with GitHub markdown CSS. New types register in src/server/renderers/ without touching routing. Lightweight CLI via: cac <path , --port , --open , --no-nav . Live content updates ride Vite's HMR channel: the server pushes a custom hmr-serve:update event and the content pane re-fetches — so Vite's client handles transport and reconnection for us. Links & URLs. Raw HTML is served at mirror paths / hmrserve/raw/<file , so relative links and assets inside a framed doc href="contact.html" , <img src="logo.png" resolve against the real folder layout. The selected file is reflected in a clean, bookmarkable URL under the served folder's name — e.g. serving ./aurora-notes gives /aurora-notes/docs/intro.md . These are real History-API paths no : shareable, reload-safe and back/forward works. Unknown paths 404 rather than rendering the app, so a stray absolute link can't nest the shell inside the content pane. src/ cli/ arg parsing + entry server/ Vite plugin, middleware, search index, watcher, renderers client/ Vue app shell tree + content pane shared/ types shared across server and client fixtures/ versioned sample files used by tests tests/ unit · component · e2e See CONTRIBUTING.md /floodtide/hmr-serve/blob/main/CONTRIBUTING.md for local setup and test expectations.