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Use for lease-scoped visible browser navigation, semantic page interaction, diagnostics, emulation, performance, audits, memory analysis, screencasts, and browser artifacts.
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Based on SOC occupation classification
| name | visible-browser-lab |
| description | Use for lease-scoped visible browser navigation, semantic page interaction, diagnostics, emulation, performance, audits, memory analysis, screencasts, and browser artifacts. |
Use this workflow when the user needs browser automation and visual confirmation in the same Chrome window.
Visible Browser Lab exposes one MCP server, visible-browser-lab. It owns tab isolation through explicit sessions and leased tab IDs.
Start the browser workflow with an MCP tool call. With no CDP configuration, Visible Browser Lab starts or reuses its managed Chrome profile and creates tabs in a visible window without activating Chrome. The managed profile persists across broker and MCP server restarts so the user can inspect and interact with its tabs.
An explicit VISIBLE_BROWSER_CDP_ENDPOINT, VISIBLE_BROWSER_CDP_PORT, or --cdp-endpoint selects an existing Chrome instance. Use this external mode when the user or development environment already owns the browser lifecycle.
VISIBLE_BROWSER_LAB_STATE_DIR selects an isolated broker and managed profile. VISIBLE_BROWSER_LAB_CHROME_PATH selects a specific Chromium-family browser executable. Leave these unset for the installed default.
Call browser operations directly. Conversation-aware hosts select the session automatically. If a call returns session_required, call start_session, keep the returned agent_session_id for the full task, and pass it on every later tool call.
Use leased tab_id values as the browser-action handles. Conversation-aware hosts supply the ambient session out of band; include agent_session_id only when recovering through the explicit fallback workflow.
Use list_tabs with its default scope for normal work. The default list shows the caller's active and missing leases and hides released or closed leases. Use global_readonly only to understand the shared visible browser inventory; it groups foreign tabs by owner_display_id and withholds foreign agent_session_id and tab_id values.
Use new_tab to create an owned background tab. Set focus: true only when the user wants Chrome activated immediately. Use claim_tab to claim an unowned Chrome target by target_id. Use takeover only when the user explicitly asks to transfer ownership, with a non-empty user_instruction; takeover returns a new leased tab_id and invalidates the previous active lease.
Use every page-scoped tool only with an owned tab_id. release_tab makes the Chrome target visible and claimable, while VBL-created targets remain eligible for cleanup when the responsible session expires. Only when the user explicitly asks to keep a VBL-created target open after the session should you pass leave_visible: true together with their non-empty user_instruction. close_tab closes the Chrome target and marks the lease closed.
Inspect an unfamiliar page with snapshot. Its compact accessibility tree assigns short ref values to elements in the main document and frames. Pass those references to click and fill. A reference remains subordinate to its session, tab lease, frame, and document; after navigation or element_stale, call snapshot again. Use { "css": "..." } only when the accessibility snapshot does not represent the target.
fill replaces one ordinary editable control. Use fill_form for two or more controls, including combined text, select, and checkbox updates. Use type_text for contenteditable controls and insertion at an established caret. Use press_key with a target for named keys or shortcuts against a resolved element. Use targetless press_key and interact click_at only after focus_tab has focused the owned document.
Mutating semantic actions return an accessibility diff by default; request observe: "snapshot" for the complete resulting tree or observe: "none" when no page observation is needed. click also returns action evidence with the delivery mode, resolved element, center hit-test, URL change, and relevant network events so quiet submits can be verified from the tool result. Navigation, waits, snapshots, screenshots, evaluation, form updates, text insertion, element-targeted click, targeted key, referenced pointer, diagnostics, and analysis preserve the user's active application. Routine actions attach to the owned target and prepare the resolved element without target activation. focus_tab and focus: true are the explicit operations for bringing managed Chrome forward when the user asks for manual inspection or handoff.
Use wait_for for asynchronous text, element, URL, load, or expression state. Use screenshot for visual appearance. Use console and network for runtime diagnosis. Use help to select an operation in interact, emulation, performance, audit, memory, screencast, or artifacts. Use evaluate or a strict CSS target only when the accessibility snapshot and named semantic tools cannot represent the required state. Do not use them to verify a semantic action.
Screencasts are broker-owned silent VP8-in-WebM jobs. screencast start defaults to 1280×720, 10 fps, quality 70, and 30 seconds; supply max_width and max_height together as even integers when overriding the size. stop waits briefly and may return finalizing; poll status or repeat stop until the same job reaches ready or error. A caller timeout does not cancel finalization, and no internal encoder or artifact handle belongs in later calls.
If a leased target disappears, keep the missing lease visible in owned listings, create or claim another tab, and continue with the new tab_id.
Browser-visible startup, auth, permission, SSO, account, scope, or team-selection steps are normal handoff points.
When one appears:
visible-browser-lab MCP server for tab lifecycle, semantic snapshots, navigation, page actions, diagnostics, emulation, analysis, capture, and artifacts.tab_id values as bearer handles. In the explicit fallback workflow, treat agent_session_id as a bearer handle too and retain both for later calls; in ambient mode, never invent or request a session handle.target_id, title, URL, and owner display information for diagnosis and handoff, not as substitutes for an owned tab_id.help to inspect a domain operation before constructing specialized arguments.Target.activateTarget, is reserved for focus_tab and focus: true.http://localhost:3002/ unless the user chooses another local port.