add_header

Chrome extension (MV3) that lets developers and QA add custom HTTP request headers on specific websites — without the DevTools ritual.

What it does

• Set headers per site (https://example.com or *.example.com)
• Toggle rules on/off globally or per site
• Headers apply via declarativeNetRequest (reliable, non-blocking)

Prerequisites

• Docker and Docker Compose
• Chrome on the host (for manual smoke only — extension runs in host browser)

All build, test, and lint commands run inside Docker. No local Node.js required.

First-time setup

make setup

Dev loop (Docker)

make check        # lint + typecheck + test
make build        # production bundle → dist/
make dev          # watch rebuild (foreground)
make test
make lint
make shell        # interactive container shell

After code changes: rebuild (or keep make dev running) and click Reload on the extension card in chrome://extensions.

Load unpacked (manual smoke)

1. make build
2. Open chrome://extensions
3. Enable Developer mode
4. Load unpacked → select the dist/ folder
5. Open Manage headers from the popup, add a rule for https://httpbin.org
6. Visit httpbin.org/headers and confirm your header appears

Isolation model

What	Where
Node, npm, dependencies	Docker volume node_modules (not on host)
Source code	Bind-mounted from host (edit locally)
Build output dist/	Written to host (Chrome loads unpacked from here)
Chrome / manual QA	Host browser only

Project docs

• Agent context: add_header_CONTEXT.md
• Agent routing: AGENTS.md
• Docker details: docs/engineering/docker.md
• Status & roadmap: docs/project/

MVP scope

In scope: per-origin header rules, popup + options UI, local storage, DNR apply.

Out of scope for now: cloud sync, Firefox/Safari, full API client, backend.