How to Use Transformers.js in a Chrome Extension

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Who this is for What we will build 1) Chrome extension architecture (MV3) 1.1 Runtime contexts and entry points 1.2 What runs where 1.3 Messaging contract 2) Transformers.js integration details 2.1 Models and responsibilities 2.2 Where inference runs 2.3 Download and cache lifecycle 3) Agent and tool execution loop 3.1 Tool-calling basics (why this layer exists) 3.2 Tool interface in this project 3.3 Loop design (Agent.runAgent) 4) Data boundaries and persistence 5) Build and packaging notes Final takeaway We recently released a Transformers.js demo browser extension powered by Gemma 4 E2B to help users navigate the web.

While building it, we ran into several practical observations about Manifest V3 runtimes, model loading, and messaging that are worth sharing.

Who this is for

This guide is for developers who want to run local AI features in a Chrome extension with Transformers.js under Manifest V3 constraints.