How to let a coding agent use a website you are signed in to

Sooner or later you ask a coding agent to do something on the web that sits behind a sign-in. Check an order. Read a dashboard. File the form. The obvious answer - let it use your browser - is the wrong one, twice over.

It no longer works: Chrome and Edge refuse to be remote-controlled on your everyday profile, and they encrypt its saved logins so they cannot be copied out. And if it did work, you would not want it. Your browser holds your whole life. An agent driving it acts as you, everywhere, on every account you have ever stayed signed in to.

Give it a browser of its own

The answer in DevThrottle is a browser profile: a real Chrome, Edge, Brave or Opera running in a separate profile with its own folder on disk and its own sign-ins, starting completely empty. You sign it in once, by hand, to exactly the accounts you want an agent to reach. From then on an agent on that machine can drive it - click, read, fill forms - through Browser Harness, the browser-driving tool DevThrottle installs for you. What the profile can act as is precisely what you signed in to, and nothing else.

Setting one up

• Open Browser profiles. It is a pinned row in the Director's left rail. If a banner says Turn on browser control, click Install Browser Harness first.
• Name it after the identity, not the task. Click + Create browser profile. "Work", "Personal" or a client's name tells you, six weeks from now, what an agent pointed there can reach. "testing" tells you nothing. Pick the browser - only ones installed on the machine are listed. Your everyday browser is not touched: not its tabs, its bookmarks or its logins.
• Sign in yourself. A new window opens and you type the credentials into it. DevThrottle opens the page, never types, and never sees a password. Sign in to a whole Google or Microsoft account, or to just the one site this profile is for - which is how a client profile holds that client's portal and nothing else. Then click Done - I am signed in.
• Know what the card means. Ready says the browser is running and you once confirmed a sign-in. It does not re-check that the site still thinks so. If a site signs the profile out later, the card still reads Ready; the tell is an agent reporting a login page, and the fix is signing in again by hand.

The logins live in the profile's own folder, so they survive a browser restart, a Director restart and a reboot - for as long as the sites keep the session.

Teaching the agent to use it

An agent does not drive the profile because it exists. Three things have to be true: the profile is running, two attach variables are set, and the thing doing the clicking is Browser Harness. Each command an agent runs is its own process, so all of it has to happen in one shell, as one block:

cc-devthrottle browser start 'work'
eval "$(cc-devthrottle browser attach 'work')"
browser-harness <<'PY'
new_tab("https://example.com")
print(page_info())
PY

start launches the profile if it is down. attach prints the two variables Browser Harness reads. The last lines open a tab and read the page back - and that read-back is your proof the attach worked.

Those variables do not redirect an agent's own built-in web tools, and telling an agent a profile name does nothing on its own. Put the block, with the profile name to use, where your agent reads its standing instructions - the repository's agent instructions file or a skill. From there its browser work lands in the profile you signed in.

A signed-in profile is a credential

An agent driving it can do anything those accounts can do. Profiles do not make that risk disappear; they make it explicit and chosen. Which identity an agent holds becomes a decision you made once, on purpose, rather than something it inherits by borrowing the browser you live in. Make one profile per identity, sign each in to only what it needs, and remember that a profile belongs to one machine - only agents on that machine can drive it.

The full walk-through, including the PowerShell form of the attach step, is Give an agent its own browser.