Overview

Pre-configure pools of reserved browsers

Browser pools let you maintain a set of reserved, identical browsers ready for immediate use. Use them to set your preferred browser configuration in advance (such as stealth, proxies, extensions, and profiles), allowing you to minimize browser start-up latency and scale your workloads in production.

Acquiring a browser from a pool is faster than creating a browser directly. Reserved browsers and on-demand browsers share the same concurrency limit, and reserved browsers aren’t billed until they’re used. See Scale for how pools fit into best practices for production architecture.

How browser pools work

Browser pools are a way to pre-configure a fixed set of browsers without being charged for them until they are used (i.e. acquired). All browsers in the pool share the same settings upon instantiation.

1. Declare a pool

   First, declare a pool of browsers with your specified configuration. The pool takes time to fill (see fill rate per minute), so declare your pool outside your browser automation / agent runtime logic.

   Pool declarations should be decoupled from browser runtime logic for the best performance.

2. Acquire a browser

   You can acquire a browser as soon as you’ve created a pool. The request returns immediately if a browser is available, or waits until one becomes available.

   The total number of browsers is fixed to the size specified upon browser pool creation. When you acquire a browser, the pool’s available count is decremented by one. When you release a browser, the pool’s available count is incremented by one.

   Put differently, the pool does not top up when you acquire a browser: browsers are “borrowed” from the pool and must be returned when you’re done with them, either by releasing them or allowing them to timeout.

3. Release a browser

   When you’re done with a browser, release it back to the pool. This step is important; otherwise, the browser will continue to be in an acquired state until it times out.

   Failing to release browsers may result in unexpected latency when acquiring future browsers.

Create a pool of reserved browsers

Create a browser pool with a specified size and configuration. All browsers in the pool share the same settings.

Typescript/Javascript

import Kernel from '@onkernel/sdk';

const kernel = new Kernel();

const pool = await kernel.browserPools.create({
  name: "my-pool",
  size: 10,
  stealth: true,
  headless: false,
  timeout_seconds: 600,
  start_url: "https://example.com",
  viewport: {
    width: 1280,
    height: 800
  }
});

console.log(pool.id);

from kernel import Kernel

kernel = Kernel()

pool = kernel.browser_pools.create(
    name="my-pool",
    size=10,
    stealth=True,
    headless=False,
    timeout_seconds=600,
    start_url="https://example.com",
    viewport={
        "width": 1280,
        "height": 800
    }
)

print(pool.id)

package main

import (
	"context"
	"fmt"

	"github.com/kernel/kernel-go-sdk"
	"github.com/kernel/kernel-go-sdk/shared"
)

func main() {
	ctx := context.Background()
	client := kernel.NewClient()

	pool, err := client.BrowserPools.New(ctx, kernel.BrowserPoolNewParams{
		Name:           kernel.String("my-pool"),
		Size:           10,
		Stealth:        kernel.Bool(true),
		Headless:       kernel.Bool(false),
		TimeoutSeconds: kernel.Int(600),
		StartURL:       kernel.String("https://example.com"),
		Viewport: shared.BrowserViewportParam{
			Width:  1280,
			Height: 800,
		},
	})
	if err != nil {
		panic(err)
	}

	fmt.Println(pool.ID)
}

Pool configuration options

Pools can be pre-configured with options like start url, custom extensions, supported viewports, residential proxies, profiles, and more. See the API reference for more details.

A profile attached to a pool is loaded read-only: pooled browsers never persist changes back to the profile, so save_changes does not apply to pools (it is silently ignored if sent). To capture profile state, use a single browser session with save_changes instead — see Profiles.

When a pool has a profile attached, refresh_on_profile_update is automatically enabled — the pool flushes idle browsers whenever the profile’s contents are updated, so it always picks up the latest profile data. See Refresh on profile update below.

Acquire a browser

Acquire a browser from the pool. The request returns immediately if a browser is available, or waits until one becomes available. The acquire_timeout_seconds parameter controls how long to wait; it defaults to the calculated time it would take to fill the pool at the pool’s configured fill rate.

Typescript/Javascript

const browser = await kernel.browserPools.acquire("my-pool", {
  acquire_timeout_seconds: 30,
});

console.log(browser.session_id);
console.log(browser.cdp_ws_url);

browser = kernel.browser_pools.acquire(
    "my-pool",
    acquire_timeout_seconds=30,
)

print(browser.session_id)
print(browser.cdp_ws_url)

browser, err := client.BrowserPools.Acquire(ctx, "my-pool", kernel.BrowserPoolAcquireParams{
	AcquireTimeoutSeconds: kernel.Int(30),
})
if err != nil {
	panic(err)
}

fmt.Println(browser.SessionID)
fmt.Println(browser.CdpWsURL)

The acquired browser includes all the same properties as a regular browser session, including cdp_ws_url for CDP connections and browser_live_view_url for live viewing.

Timeout behavior

Browsers remain in the pool indefinitely until acquired. Once acquired, the pool’s timeout_seconds applies just like a regular browser timeout—if the browser is idle (no CDP or live view connection) for longer than the timeout, it is destroyed and not returned to the pool. The pool will automatically create a replacement browser at the pool’s configured fill rate.

Release a browser

When you’re done with a browser, release it back to the pool. By default, the browser instance is reused. Set reuse: false to destroy it and create a fresh one.

Typescript/Javascript

await kernel.browserPools.release("my-pool", {
  session_id: browser.session_id,
  reuse: true,
});

kernel.browser_pools.release(
    "my-pool",
    session_id=browser.session_id,
    reuse=True,
)

if err := client.BrowserPools.Release(ctx, "my-pool", kernel.BrowserPoolReleaseParams{
	SessionID: browser.SessionID,
	Reuse:     kernel.Bool(true),
}); err != nil {
	panic(err)
}

Update a pool

Update the pool configuration. By default, existing idle browsers keep their current configuration and only newly created browsers use the new one. Pass discard_all_idle: true to discard all idle browsers and rebuild them immediately with the new configuration.

Typescript/Javascript

const updatedPool = await kernel.browserPools.update("my-pool", {
  size: 20,
  stealth: true,
});

updated_pool = kernel.browser_pools.update(
    "my-pool",
    size=20,
    stealth=True,
)

updatedPool, err := client.BrowserPools.Update(ctx, "my-pool", kernel.BrowserPoolUpdateParams{
	Size:    20,
	Stealth: kernel.Bool(true),
})
if err != nil {
	panic(err)
}
_ = updatedPool

The size parameter is always required when updating a pool, even if you only want to change other settings.

By default (discard_all_idle: false), updating a pool leaves existing idle browsers untouched — they keep their original configuration, and only browsers created after the update use the new configuration. Set discard_all_idle: true to discard all idle browsers and rebuild them immediately with the new configuration.

Refresh on profile update

When a pool is configured with a profile, the profile data is loaded into each browser when it’s created. Normally, updating the profile’s contents (for example, re-saving cookies or auth state to the same profile) does not propagate to already-warmed browsers — only newly-filled browsers use the updated profile.

refresh_on_profile_update is automatically set to true when a pool is created with a profile, or when an existing pool’s profile is changed. This ensures that acquired browsers always get the latest profile data without manual intervention. You can explicitly set it to false to opt out.

When a pool’s profile is removed (by passing { "id": "" }), refresh_on_profile_update is forced to false.

refresh_on_profile_update requires a profile to be set on the pool. Setting it explicitly to true on a pool without a profile returns a validation error. When created without a profile, it defaults to false.

How it works

When a profile is saved (for example, after a successful Managed Auth login or a save_changes browser session), Kernel checks whether any browser pools use that profile with refresh_on_profile_update enabled. If so, all idle browsers in each matching pool are flushed — they are replaced with fresh browsers that load the updated profile. Acquired browsers are not affected; they continue running with the profile data they were created with.

Reused browsers keep the configuration they were created with. A plain update() rebuilds nothing that already exists — it only changes the config used for future browsers. To rebuild the idle browsers too, pass discard_all_idle: true (or call flush()). Either way, browsers that are acquired during an update are never touched: an in-use browser keeps its original configuration, and if you then release it with reuse: true (the default) it re-enters the pool still carrying that stale configuration and keeps getting handed out that way.

You have three ways to get an in-use browser onto the new configuration:

• Prevent it on release: release with reuse: false. The browser is destroyed and rebuilt with the current pool configuration instead of the old one returning to the pool.
• Let it expire: don’t release the acquired browser for reuse. Let it reach its timeout_seconds while idle, at which point it’s destroyed and the pool refills automatically with the new configuration.
• Clean it up after the fact: flush() the pool, or run a later update() with discard_all_idle: true, once the in-use browsers have been released.

Flush idle browsers

Destroy all idle browsers in the pool. Acquired browsers are not affected. The pool will automatically refill with the pool’s specified configuration.

Typescript/Javascript

await kernel.browserPools.flush("my-pool");

kernel.browser_pools.flush("my-pool")

if err := client.BrowserPools.Flush(ctx, "my-pool"); err != nil {
	panic(err)
}

Get pool details

Retrieve the current status and configuration of a pool.

Typescript/Javascript

const pool = await kernel.browserPools.retrieve("my-pool");

console.log(pool.available_count);
console.log(pool.acquired_count);

pool = kernel.browser_pools.retrieve("my-pool")

print(pool.available_count)
print(pool.acquired_count)

pool, err := client.BrowserPools.Get(ctx, "my-pool")
if err != nil {
	panic(err)
}

fmt.Println(pool.AvailableCount)
fmt.Println(pool.AcquiredCount)

List pools

List all browser pools in your organization.

Typescript/Javascript

const pools = await kernel.browserPools.list();

for (const pool of pools) {
  console.log(pool.name, pool.available_count);
}

pools = kernel.browser_pools.list()

for pool in pools:
    print(pool.name, pool.available_count)

pools, err := client.BrowserPools.List(ctx)
if err != nil {
	panic(err)
}

for _, pool := range *pools {
	fmt.Println(pool.Name, pool.AvailableCount)
}

Delete a pool

Delete a browser pool and all browsers in it. By default, deletion is blocked if browsers are currently acquired. Use force: true to terminate acquired browsers and force deletion.

Typescript/Javascript

// Delete a pool (fails if browsers are acquired)
await kernel.browserPools.delete("my-pool");

// Force delete even if browsers are acquired
await kernel.browserPools.delete("my-pool", { force: true });

# Delete a pool (fails if browsers are acquired)
kernel.browser_pools.delete("my-pool")

# Force delete even if browsers are acquired
kernel.browser_pools.delete("my-pool", force=True)

// Delete a pool (fails if browsers are acquired)
if err := client.BrowserPools.Delete(ctx, "my-pool", kernel.BrowserPoolDeleteParams{}); err != nil {
	panic(err)
}

// Force delete even if browsers are acquired
if err := client.BrowserPools.Delete(ctx, "my-pool", kernel.BrowserPoolDeleteParams{
	Force: kernel.Bool(true),
}); err != nil {
	panic(err)
}

Full example

This example assumes you’ve already created a pool named “my-pool”. In practice, you’d create pools once (via the SDK, CLI, or dashboard) and then acquire from them repeatedly.

Typescript/Javascript

import Kernel from '@onkernel/sdk';
import { chromium } from 'playwright';

const kernel = new Kernel();

// Acquire a browser from an existing pool
const kernelBrowser = await kernel.browserPools.acquire("my-pool", {});

try {
  // Connect via CDP
  const browser = await chromium.connectOverCDP(kernelBrowser.cdp_ws_url);
  const context = browser.contexts()[0];
  const page = context.pages()[0];

  await page.goto('https://example.com');
  const title = await page.title();
  console.log(title);
} finally {
  // Release back to pool for reuse
  await kernel.browserPools.release("my-pool", {
    session_id: kernelBrowser.session_id,
  });
}

import asyncio
from kernel import Kernel
from playwright.async_api import async_playwright

kernel = Kernel()

async def main():
    # Acquire a browser from an existing pool
    kernel_browser = kernel.browser_pools.acquire("my-pool")

    async with async_playwright() as playwright:
        try:
            # Connect via CDP
            browser = await playwright.chromium.connect_over_cdp(kernel_browser.cdp_ws_url)
            context = browser.contexts[0]
            page = context.pages[0]

            await page.goto('https://example.com')
            title = await page.title()
            print(title)
        finally:
            # Release back to pool for reuse
            kernel.browser_pools.release(
                "my-pool",
                session_id=kernel_browser.session_id,
            )

asyncio.run(main())

package main

import (
	"context"
	"fmt"

	"github.com/kernel/kernel-go-sdk"
)

func main() {
	ctx := context.Background()
	client := kernel.NewClient()

	// Acquire a browser from an existing pool
	kernelBrowser, err := client.BrowserPools.Acquire(ctx, "my-pool", kernel.BrowserPoolAcquireParams{})
	if err != nil {
		panic(err)
	}

	defer func() {
		// Release back to pool for reuse
		if err := client.BrowserPools.Release(ctx, "my-pool", kernel.BrowserPoolReleaseParams{
			SessionID: kernelBrowser.SessionID,
		}); err != nil {
			panic(err)
		}
	}()

	response, err := client.Browsers.Playwright.Execute(ctx, kernelBrowser.SessionID, kernel.BrowserPlaywrightExecuteParams{
		Code: `
			await page.goto('https://example.com');
			return await page.title();
		`,
	})
	if err != nil {
		panic(err)
	}

	fmt.Println(response.Result)
}

API reference

For more details on all available endpoints and parameters, see the Browser Pools API reference.