Plasmo is a development platform for browser extensions, small programs that add features to browsers such as Chrome, Firefox and Edge. Made by Plasmo Corp., its main product is the Plasmo Framework, an open-source SDK (software development kit) that its README compares to Next.js for browser extensions.
A developer starts a project with pnpm create plasmo and writes ordinary files: popup.tsx for the popup, options.tsx for the options page, content.ts for content scripts that run inside web pages, and background.ts for the background service worker. The framework bundles and mounts these files and takes care of the configuration files, so the developer writes little boilerplate. It supports React, TypeScript, Svelte and Vue, reloads the extension live during development, includes storage and messaging libraries, and builds one code base for several browsers and manifest versions. Plasmo BPP, an open-source GitHub Action, publishes the finished extension to the Chrome, Firefox and Edge stores, and Itero TestBed, a hosted service, pushes updates to beta testers without store review.
The Plasmo Framework is free and open source under the MIT license.