> For the complete documentation index, see [llms.txt](https://docs.unbrowse.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.unbrowse.ai/for-agents/when-it-uses-a-browser.md).

# When It Uses a Browser

Unbrowse keeps a real browser in the loop only when the site genuinely depends on browser-bound state, and treats opening one as a cost to avoid, not a feature.

A browser session is used when the task needs things a bare request cannot carry:

* sign-in and session cookies
* cross-site request tokens
* redirect chains
* stricter authenticated single-page behaviour

For everything else, the reused route is cheaper and faster, so that path is preferred.

When live capture is unavoidable, Unbrowse opens a browse session, the agent drives it (navigate, snapshot, click, fill, submit), and the traffic is indexed passively so the next agent with the same intent does not have to repeat the session. The result is that browser use trends toward zero as the shared graph fills, rather than being paid on every run.

The operating principle: a browser open during normal operation is a multi-step event to be designed out, not relied on.

## Truth and capability boundaries

Browser driving supports Chrome/Chromium. Importing cookies from another browser does not mean that browser family can be driven. Results expose `static_unevaluated` or `javascript_evaluated`; static content cannot satisfy a task that requires evaluated JavaScript. Stealth is best-effort and `stealth_guaranteed` is always false.

Cookie presentation and successful navigation do not prove login. Auth-bearing flows report `auth_outcome` (`not_presented`, `presented_accepted`, `presented_rejected`, or `presented_unknown`) and may terminate with `auth_required` or `session_expired`.

Capability failures are explicit: `chromium_unavailable`, `chromium_cdp_unavailable`, and `kuri_sandbox_unavailable`. Cloudflare, PerimeterX, and `empty_capture` blockers are reported separately. Follow a `next_step` only when its required runtime is available; Unbrowse does not claim to bypass every challenge.