📄 playwright-python/python/docs/api/class-clock

File: class-clock.md | Updated: 11/18/2025

Source: https://playwright.dev/python/docs/api/class-clock

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Accurately simulating time-dependent behavior is essential for verifying the correctness of applications. Learn more about clock emulation .

Note that clock is installed for the entire BrowserContext , so the time in all the pages and iframes is controlled by the same clock.

Methods​

fast_forward​

Added in: v1.45 clock.fast_forward

Advance the clock by jumping forward in time. Only fires due timers at most once. This is equivalent to user closing the laptop lid for a while and reopening it later, after given time.

Usage

  • Sync

  • Async

    page.clock.fast_forward(1000)page.clock.fast_forward("30:00")

    await page.clock.fast_forward(1000)await page.clock.fast_forward("30:00")

Arguments

  • ticks int | str #

    Time may be the number of milliseconds to advance the clock by or a human-readable string. Valid string formats are "08" for eight seconds, "01:00" for one minute and "02:34:10" for two hours, 34 minutes and ten seconds.

Returns

install​

Added in: v1.45 clock.install

Install fake implementations for the following time-related functions:

  • Date
  • setTimeout
  • clearTimeout
  • setInterval
  • clearInterval
  • requestAnimationFrame
  • cancelAnimationFrame
  • requestIdleCallback
  • cancelIdleCallback
  • performance

Fake timers are used to manually control the flow of time in tests. They allow you to advance time, fire timers, and control the behavior of time-dependent functions. See clock.run_for() and clock.fast_forward() for more information.

Usage

clock.install()clock.install(**kwargs)

Arguments

  • time float | str | datetime (optional)#

    Time to initialize with, current system time by default.

Returns

pause_at​

Added in: v1.45 clock.pause_at

Advance the clock by jumping forward in time and pause the time. Once this method is called, no timers are fired unless clock.run_for() , clock.fast_forward() , clock.pause_at() or clock.resume() is called.

Only fires due timers at most once. This is equivalent to user closing the laptop lid for a while and reopening it at the specified time and pausing.

Usage

  • Sync

  • Async

    page.clock.pause_at(datetime.datetime(2020, 2, 2))page.clock.pause_at("2020-02-02")

    await page.clock.pause_at(datetime.datetime(2020, 2, 2))await page.clock.pause_at("2020-02-02")

For best results, install the clock before navigating the page and set it to a time slightly before the intended test time. This ensures that all timers run normally during page loading, preventing the page from getting stuck. Once the page has fully loaded, you can safely use clock.pause_at() to pause the clock.

  • Sync

  • Async

    Initialize clock with some time before the test time and let the page load# naturally. Date.now will progress as the timers fire.page.clock.install(time=datetime.datetime(2024, 12, 10, 8, 0, 0))page.goto("http://localhost:3333")page.clock.pause_at(datetime.datetime(2024, 12, 10, 10, 0, 0))

    Initialize clock with some time before the test time and let the page load# naturally. Date.now will progress as the timers fire.await page.clock.install(time=datetime.datetime(2024, 12, 10, 8, 0, 0))await page.goto("http://localhost:3333")await page.clock.pause_at(datetime.datetime(2024, 12, 10, 10, 0, 0))

Arguments

Returns

resume​

Added in: v1.45 clock.resume

Resumes timers. Once this method is called, time resumes flowing, timers are fired as usual.

Usage

clock.resume()

Returns

run_for​

Added in: v1.45 clock.run_for

Advance the clock, firing all the time-related callbacks.

Usage

  • Sync

  • Async

    page.clock.run_for(1000);page.clock.run_for("30:00")

    await page.clock.run_for(1000);await page.clock.run_for("30:00")

Arguments

  • ticks int | str #

    Time may be the number of milliseconds to advance the clock by or a human-readable string. Valid string formats are "08" for eight seconds, "01:00" for one minute and "02:34:10" for two hours, 34 minutes and ten seconds.

Returns

set_fixed_time​

Added in: v1.45 clock.set_fixed_time

Makes Date.now and new Date() return fixed fake time at all times, keeps all the timers running.

Use this method for simple scenarios where you only need to test with a predefined time. For more advanced scenarios, use clock.install() instead. Read docs on clock emulation to learn more.

Usage

  • Sync

  • Async

    page.clock.set_fixed_time(datetime.datetime.now())page.clock.set_fixed_time(datetime.datetime(2020, 2, 2))page.clock.set_fixed_time("2020-02-02")

    await page.clock.set_fixed_time(datetime.datetime.now())await page.clock.set_fixed_time(datetime.datetime(2020, 2, 2))await page.clock.set_fixed_time("2020-02-02")

Arguments

Returns

set_system_time​

Added in: v1.45 clock.set_system_time

Sets system time, but does not trigger any timers. Use this to test how the web page reacts to a time shift, for example switching from summer to winter time, or changing time zones.

Usage

  • Sync

  • Async

    page.clock.set_system_time(datetime.datetime.now())page.clock.set_system_time(datetime.datetime(2020, 2, 2))page.clock.set_system_time("2020-02-02")

    await page.clock.set_system_time(datetime.datetime.now())await page.clock.set_system_time(datetime.datetime(2020, 2, 2))await page.clock.set_system_time("2020-02-02")

Arguments

Returns