Init Scripts & Extensions#

Init scripts run before page JavaScript. Use them to install hooks, polyfills, instrumentation, or test helpers before the first navigation.

Launch-time scripts#

agent-browser --init-script ./instrumentation.js open https://example.com
agent-browser --init-script ./a.js --init-script ./b.js open https://example.com

You can also configure scripts with an environment variable:

export AGENT_BROWSER_INIT_SCRIPTS="./a.js,./b.js"
agent-browser open https://example.com

Launch-time scripts are applied when the browser starts. If the daemon is already running, close it before changing launch-time script options.

Built-in scripts#

agent-browser --enable react-devtools open http://localhost:3000

react-devtools is the built-in feature currently available. It installs the React DevTools hook before application code runs and is required for react tree, react inspect, react renders, and react suspense.

Runtime scripts#

agent-browser addinitscript "window.__testMode = true"
# Returns an identifier

agent-browser removeinitscript <identifier>

Runtime init scripts are useful after a session has started. They are still init scripts, so they affect future documents and navigations rather than rewriting already-executed page code.

For flows that need routes, cookies, or scripts installed before the first real navigation, start the browser without a URL:

agent-browser batch \
  '["open"]' \
  '["network","route","*","--abort","--resource-type","script"]' \
  '["cookies","set","--curl","cookies.curl","--domain","localhost"]' \
  '["navigate","http://localhost:3000/target"]'

open with no URL launches the browser on about:blank, leaving room to stage state before the target page loads.

Extensions#

agent-browser --extension ./extension open https://example.com
agent-browser --extension ./a --extension ./b open https://example.com

Extensions are launch-time options. They require a local Chromium-based browser and are not supported with CDP connections, cloud providers, or Lightpanda.

Safety#