open_session

open_session

Start a browser session. Do this first.

MCP tool	open_session
HTTP	POST /browser/open

This is the only place a browser is created, and the only place its settings can be chosen, so it is never done implicitly for you.

Set width and height when layout matters — the headless default is narrow and varies between Grid nodes. page_load_timeout bounds how long a navigation may hang; without one a stuck page holds a scarce Grid slot until the Grid reaps it.

The returned session_id is what a stateless caller passes to every later call. If this server is holding the browser for you, it is returned for information and you should NOT pass it back — read the session://current resource if you are unsure which of the two you are.

Parameters

Name	Type	Required	Default
url	string	no	—
width	integer	no	—
height	integer	no	—
page_load_timeout	integer	no	—
script_timeout	integer	no	—

Returns

Field	Type	Notes
session_id	string	Pass this to every other call.
url	string	Current URL after the action.
title	string	Page title after the action.
width	integer	Window width in use.
height	integer	Window height in use.
settings	object	The settings this session actually opened with, after the server default / client default / explicit cascade.

Errors are 400 for a bad argument, 401 without a token, 500 when the Grid refuses. Over MCP the same failures arrive as a tool error.

Example

MCP

open_session()

HTTP

curl -X POST $SELENIUM_FLOW/browser/open \
  -H "Authorization: Bearer $TOKEN" \
  -H 'Content-Type: application/json' \
  -d '{
    "session_id": "…"
  }'

---

← All actions · Installing · Deployment