> ## Documentation Index
> Fetch the complete documentation index at: https://docs.browseract.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Concurrency & Isolation

> Understand how browsers and sessions let agents run parallel work without state leaks.

Browser-act separates **identity** from **work**:

* A **browser** is an identity: cookies, profile, fingerprint, proxy, and description.
* A **session** is a workspace: one task's current page, tabs, state, and command flow.

This model lets agents run multiple tasks without mixing state.

## Concurrency models

<div style={{ display: "flex", justifyContent: "center" }}>
  ```mermaid theme={null}
  flowchart TD
    Task["Agent work"] --> Cross["Separate browsers"]
    Task --> Shared["Shared browser"]
    Task --> Private["Private sessions"]
  ```
</div>

| Model                            | Isolation level           | Shared state            | Best for                                  |
| -------------------------------- | ------------------------- | ----------------------- | ----------------------------------------- |
| Cross-browser parallelism        | Browser identity          | Nothing by default      | Multiple accounts, regions, or identities |
| Multiple sessions on one browser | Session workspace         | Cookies and login state | Parallel tasks on the same account        |
| Stealth privacy sessions         | Fresh profile per session | Nothing persistent      | One-off public data collection            |

## Cross-browser parallelism

Each browser has independent cookies, fingerprints, and proxy settings.

```bash theme={null}
browser-act --session account-a browser open <browser_a_id> https://example.com
browser-act --session account-b browser open <browser_b_id> https://example.com
```

Session names must be globally unique. Use names that describe the task and identity.

## Multiple sessions on one browser

Use multiple sessions when tasks should share the same login state but run independently:

```bash theme={null}
browser-act --session inbox-check browser open <browser_id> https://example.com/inbox
browser-act --session report-export browser open <browser_id> https://example.com/reports
```

Both sessions share the browser's cookies and profile, but navigation and current page state are separate.

## Privacy mode sessions

For stealth browsers with `--private true`, each session starts with a fresh fingerprint and empty profile:

```bash theme={null}
browser-act browser create \
  --type stealth \
  --name "private-runner" \
  --desc "Fresh identity for one-off collection" \
  --private true
```

This avoids residue between jobs. The trade-off is that login state is not kept.

## Session lifecycle

<div style={{ display: "flex", justifyContent: "center" }}>
  ```mermaid theme={null}
  flowchart TD
    Open["Open"] --> State1["State"]
    State1 --> Act["Act"]
    Act --> State2["State again"]
    State2 --> Repeat{"More?"}
    Repeat -->|Yes| Act
    Repeat -->|No| Close["Close"]
  ```
</div>

Rules:

* A session belongs to the agent or task that created it.
* A session is tied to one browser.
* One browser can have multiple sessions.
* Session names must be unique.
* Idle sessions may be reclaimed automatically after a period of inactivity.

List and close sessions:

```bash theme={null}
browser-act session list
browser-act session close <session_name>
```

## Commands that do not need a session

These commands operate outside a browser workspace:

* `browser list`
* `browser create`
* `browser update`
* `browser delete`
* `browser regions`
* `browser list-profiles`
* `session list`
* `auth login`, `auth poll`, `auth set`, `auth clear`
* `get-skills`
* `report-log`
* `feedback`
* `stealth-extract`

## Best practices

> \[!TIP]
> Use descriptive session names such as `pricing-us`, `login-check`, or `report-export`. Close sessions when the task is complete.

<Columns cols={2}>
  <Card title="Shared account work" icon="copy">
    Use multiple sessions when tasks should share one browser identity and login state.
  </Card>

  <Card title="Separate identities" icon="fingerprint">
    Use separate browsers when tasks need separate accounts, regions, cookies, or proxies.
  </Card>

  <Card title="One-off jobs" icon="shield">
    Use privacy mode for work that should leave no persistent profile state.
  </Card>

  <Card title="Readable ownership" icon="tag">
    Name sessions by task and identity so agents and humans can understand what each session is doing.
  </Card>
</Columns>

## Learn more

<Columns cols={3}>
  <Card title="Browser Modes" icon="panel-top" href="/agent-cli/browser-modes" cta="Choose identity">
    Choose the right browser identity before running parallel work.
  </Card>

  <Card title="Designed for Agents" icon="brain-circuit" href="/agent-cli/designed-for-agents" cta="Understand rules">
    See how naming, selection, and safety rules help agents operate cleanly.
  </Card>

  <Card title="Command Reference" icon="terminal" href="/agent-cli/command-reference" cta="Find commands">
    Look up browser and session management commands.
  </Card>
</Columns>