Castlet

castlet is a free screen recorder that lives in a browser tab. Record your screen, camera and mic, trim the result, and save an MP4. No account, no install, and nothing is uploaded: every recording is made, stored and edited on your own computer.

I built it because the popular tools (Loom, Screencastify) push your videos to their cloud, cap free recordings, and ask you to sign up before you can record a 2 minute bug report.

What it does

• Records screen, webcam and mic, with system audio mixed in
• Floating webcam bubble and controls that stay on top of other windows (Document Picture-in-Picture)
• Markers while recording (Alt+Shift+M), shown on the timeline so you can jump back to them
• Trim and cut, remove audio, and copy any frame as an image
• Survives crashes and refreshes: an interrupted recording can be recovered
• Installs as an app and works offline

How it works

• Capture: getDisplayMedia and getUserMedia, with the Web Audio API mixing mic and system audio, and MediaRecorder writing 1 second chunks.
• Storage: chunks stream to the Origin Private File System (OPFS) while recording, so a long recording never sits in memory and a crash loses at most a second. The library (titles, dates, thumbnails) lives in IndexedDB through Dexie.
• Export: Mediabunny remuxes WebM to MP4 and handles trims and cuts in the browser, without ffmpeg.wasm. Files save with showSaveFilePicker, or a normal download as a fallback.
• Privacy: no server, no database, no login. The Content Security Policy only allows anonymous page counts (Umami), so the "never leaves your computer" promise is enforced by the browser, not just stated.
• Quality: Vitest for units, Playwright end-to-end tests that record with fake camera and screen devices in CI.

Built with React, TypeScript, Vite, Tailwind, shadcn/ui and Zustand, deployed as a static PWA on Cloudflare Pages.