Browser CLI

@msw-dev-tool/browser-cli lets an AI agent control an in-browser MSW Dev Tool session through Chrome DevTools Protocol (CDP). It uses the same handler commands and JSON output conventions as the Node CLI, but requires an explicit browser tab.

Install

pnpm add -D @msw-dev-tool/browser-cli @msw-dev-tool/core msw

Start the Chrome instance controlled by your AI with a remote-debugging port. Use a separate profile: this port gives local processes full browser-debugging access.

/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome \
  --remote-debugging-port=9222 \
  --user-data-dir=/tmp/msw-dev-tool-chrome

Configure your AI agent’s Chrome DevTools MCP server to connect to the same endpoint. For example, in Codex add the following to .codex/config.toml and restart the MCP session:

[mcp_servers.chrome-devtools]
command = "npx"
args = ["-y", "chrome-devtools-mcp@latest", "--browser-url=http://127.0.0.1:9222"]

Your MCP client and msw-dev-tool-browser can then inspect the same Chrome tabs. See the Chrome DevTools MCP guide for connecting to a running Chrome instance  for other operating systems and remote-debugging details.

Your application must call setupDevToolWorker(...handlers) in the target tab. That registers the in-page control endpoint used by the CLI.

Choose a tab

sessionStorage is scoped to a tab, even for pages on the same origin. List the available page targets and copy the intended id:

msw-dev-tool-browser tabs --cdp-url http://127.0.0.1:9222

Every other command requires both --cdp-url and --target:

msw-dev-tool-browser list --cdp-url http://127.0.0.1:9222 --target <target-id>
msw-dev-tool-browser set-behavior '<handler-id>' delay --cdp-url http://127.0.0.1:9222 --target <target-id>

Commands

msw-dev-tool-browser session --cdp-url ... --target <target-id>
msw-dev-tool-browser list --cdp-url ... --target <target-id>
msw-dev-tool-browser get '<handler-id>' --cdp-url ... --target <target-id>
msw-dev-tool-browser set-behavior '<handler-id>' delay --cdp-url ... --target <target-id>
msw-dev-tool-browser add-temp --json '<temp-handler-json>' --cdp-url ... --target <target-id>
msw-dev-tool-browser remove-temp '<handler-id>' --cdp-url ... --target <target-id>
msw-dev-tool-browser reset --cdp-url ... --target <target-id>

All commands print JSON. Changes are applied immediately: the CLI calls the same in-memory handler store used by the Dev Tool UI and persists the resulting state to sessionStorage. A refresh is only needed to confirm persisted state survives page reload, not to apply a CLI mutation.

reset immediately restores handlers from the code supplied to setupDevToolWorker(). If a target reports that no browser session is initialized, open the tab where that setup function has run.