Performance features reference

This page is a comprehensive reference of DevTools features that are related to analyzing performance.

For a step-by-step tutorial on how to analyze the performance of a page using the Performance tool, see Introduction to the Performance tool.

Record performance

Record runtime performance

Record runtime performance when you want to analyze the performance of a page as it is running, as opposed to loading.

1. Go to the page that you want to analyze.

2. Click the Performance tool in DevTools.

3. Click the Record () button.

   

4. Interact with the page. DevTools records all page activity that occurs as a result of your interactions.

5. Click Record again or click Stop to stop recording.

Record load performance

Record load performance when you want to analyze the performance of a page as it is loading, as opposed to running.

1. Go to the page that you want to analyze.

2. In DevTools, open the Performance tool.

3. Click the Refresh page () button. DevTools records performance metrics while the page refreshes and then automatically stops the recording a couple seconds after the load finishes.

DevTools automatically zooms in on the portion of the recording where most of the activity occurred.

Capture screenshots while recording

To capture a screenshot of every frame while recording, select the Screenshots checkbox.

To learn how to interact with screenshots, see View a screenshot.

Force garbage collection while recording

While you are recording a page, click Collect garbage () to force garbage collection.

Show recording settings

Click Capture settings () to expose more settings related to how DevTools captures performance recordings.

Disable JavaScript samples

By default, the Main section of a recording displays detailed call stacks of JavaScript functions that were called during the recording. To disable these call stacks:

1. Open the Capture settings menu. See Show recording settings.

2. Turn on the Disable JavaScript Samples checkbox.

3. Take a recording of the page.

The following two figures show the difference between disabling and enabling JavaScript samples. The Main section of the recording is much shorter when sampling is disabled, because it omits all of the JavaScript call stacks.

An example of a recording when JS samples are disabled:

An example of a recording when JS samples are turned on:

Throttle the network while recording

To throttle the network while recording:

1. Open the Capture settings menu. See Show recording settings.

2. Set Network to the desired level of throttling.

Throttle the CPU while recording

To throttle the CPU while recording:

1. Open the Capture settings menu. See Show recording settings.

2. Set CPU to the desired level of throttling.

Throttling is relative to the capabilities of your computer. For example, the 2x slowdown option makes your CPU operate 2 times slower than normal. DevTools don't truly simulate the CPUs of mobile devices, because the architecture of mobile devices is very different from that of desktops and laptops.

Turn on advanced paint instrumentation

To view detailed paint instrumentation:

1. Open the Capture settings menu. See Show recording settings.

2. Check the Enable advanced paint instrumentation (slow) checkbox.

To learn how to interact with the paint information, see View layers and View paint profiler.

Save a recording

To save a recording, right-click the recording and then select Save Profile.

Load a recording

To load a recording, right-click the recording and then select Load Profile.

Clear the previous recording

After making a recording, click Clear recording () to clear that recording from the Performance tool.

Analyze a performance recording

After you record runtime performance or record load performance, the Performance tool provides a lot of data for analyzing the performance of what just happened.

Select a portion of a recording

Drag your mouse left or right across the Overview to select a portion of a recording. The Overview is the section that contains the FPS, CPU, and NET charts.

To select a portion using the keyboard:

1. Select the background of the Main section, or any of the sections next to it, such as Interactions, Network, or GPU. This keyboard workflow only works when one of these sections is in focus.

2. Use the W, A, S, D keys to zoom in, move left, zoom out, and move right, respectively.

To select a portion using a trackpad:

1. Hover your mouse over the Overview section or the Details section. The Overview section is the area containing the FPS, CPU, and NET charts. The Details section is the area containing the Main section, the Interactions section, and so on.

2. Using two fingers, swipe up to zoom out, swipe left to move left, swipe down to zoom in, and swipe right to move right.

To scroll a long flame chart in the Main section or any of the neighbors, click and hold while dragging up and down. Drag left and right to move what portion of the recording is selected.

Search activities

Press Ctrl+F (Windows, Linux) or Command+F (macOS) to open the search box at the bottom of the Performance tool.

To navigate activities that match your query:

1. Click the Previous () and Next () buttons.

2. To select the next activity, press Enter. To select the previous activity, press Shift+Enter.

To modify query settings:

• To make the query case-sensitive, click the Case sensitive () button.

• To use a regular expression in your query, click the Regex () button.

To hide the search box, click Cancel.

View main thread activity

Use the Main section to view activity that occurred on the main thread of the page.

Select an event to view more information about it in the Summary tab. DevTools outlines the selected event.

DevTools represents main thread activity with a flame chart. The x-axis represents the recording over time. The y-axis represents the call stack. The events on top cause the events below it.

In the previous figure, a click event caused a Function Call in activitytabs.js on line 53. Below Function Call, review that an anonymous function was run. The anonymous function requested a, which requested wait, which requested Minor GC.

DevTools assigns scripts random colors. In the previous figure, function requests from one script are colored light green. Requests from another script are colored beige. The darker yellow represents scripting activity, and the purple event represents rendering activity. These darker yellow and purple events are consistent across all recordings.

If you want to hide the detailed flame chart of JavaScript requests, see Disable JavaScript samples, above. When JS samples are disabled, only high-level events such as Event: click and Function Call from the previous figure are displayed.

View activities in a table

After recording a page, you don't need to rely solely on the Main section to analyze activities. DevTools also provides three tabular views for analyzing activities. Each view gives you a different perspective on the activities:

• To view the activities where the most time was directly spent, use the Bottom-Up tab.

• To view the root activities that cause the most work, use the Call Tree tab.

• To view the activities in the order in which they occurred during the recording, use the Event Log tab.

Root activities

Open the Activity Tabs Demo webpage in a new window or tab. The activity tabs are the Bottom-Up, Call Tree, and Event Log tabs at the bottom of the Performance tool. These tabs display root activities.

Root activities are activities that cause the browser to do some work. For example, when you click a webpage, the browser runs an Event activity as the root activity. That Event activity may cause other activities to run, such as a handler.

In the flame chart of the Main section, root activities are at the top of the chart. In the Call Tree and Event Log tabs, root activities are the top-level items.

For an example of root activities, see The Call Tree tab, below.

The Bottom-Up tab

Open the Activity Tabs Demo webpage in a new window or tab.

Use the Bottom-Up tab to view which activities directly took up the most time in aggregate.

The Bottom-Up tab only displays activities during the selected portion of the recording. See Select a portion of a recording to learn how to select portions.

In the Main section flame chart of the previous figure, you can see that almost practically all of the time was spent running Parse HTML. The top activity in the Bottom-Up tab of the previous figure is Parse HTML. In the Bottom-Up tab, the next most expensive activity is Layout.

The Self Time column represents the aggregated time spent directly in that activity, across all of the occurrences.

The Total Time column represents aggregated time spent in that activity or any of the children.

The Call Tree tab

Open the Activity Tabs Demo webpage in a new window or tab.

Use the Call Tree tab to view which root activities cause the most work.

The Call Tree tab only displays activities during the selected portion of the recording. See Select a portion of a recording to learn how to select portions.

In the previous figure, the top-level of items in the Activity column, such as Evaluate Script and Parse HTML are root activities. The nesting represents the call stack. For example, in the previous figure, Parse HTML which caused Evaluate Script which caused Compile Script and (anonymous).

Self Time represents the time directly spent in that activity. Total Time represents the time spent in that activity or any of the children.

Click Self Time, Total Time, or Activity to sort the table by that column.

Use the Filter text box to filter events by activity name.

By default the Grouping menu is set to No Grouping. Use the Grouping menu to sort the activity table based on various criteria.

Click Show Heaviest Stack () to reveal another table to the right of the Activity table. Click on an activity to populate the Heaviest Stack table. The Heaviest Stack table displays which children of the selected activity took the longest time to run.

The Event Log tab

Use the Event Log tab to view activities in the order in which they occurred during the recording.

The Event Log tab only displays activities during the selected portion of the recording. See Select a portion of a recording to learn how to select portions.

The Start Time column represents the point at which that activity started, relative to the start of the recording. For example, the start time of 175.7 ms for the selected item in the previous figure means that activity started 175.7 ms after the recording started.

The Self Time column represents the time spent directly in that activity.

The Total Time columns represents time spent directly in that activity or in any of the children.

Click Start Time, Self Time, or Total Time to sort the table by that column.

Use the Filter text box to filter activities by name.

Use the Duration menu to filter out any activities that took less than 1 ms or 15 ms. By default the Duration menu is set to All, meaning all activities are shown.

Disable the Loading, Scripting, Rendering, or Painting checkboxes to filter out all activities from those categories.

View GPU activity

View GPU activity in the GPU section.

View raster activity

View raster activity in the Raster section.

View interactions

Use the Interactions section to find and analyze user interactions that happened during the recording.

A red line at the bottom of an interaction represents time spent waiting for the main thread.

Click an interaction to view more information about it in the Summary tab.

Analyze frames per second (FPS)

DevTools provides numerous ways to analyze frames per second:

• Use the FPS chart to get an overview of FPS over the duration of the recording.
• Use the Frames section to view how long a particular frame took.
• Use the FPS meter for a realtime estimate of FPS as the page runs. See View frames per second in realtime with the FPS meter.

The FPS chart

The FPS chart provides an overview of the frame rate across the duration of a recording. In general, the higher the green bar, the better the frame rate.

A red bar above the FPS chart is a warning that the frame rate dropped so low that it probably harmed the user's experience.

The Frames section

The Frames section tells you exactly how long a particular frame took.

Hover over a frame to view a tooltip with more information about it.

Select a frame to view more information about the frame in the Summary tab at the bottom of the Performance tool. DevTools outlines the selected frame in blue.

View network requests

Expand the Network section to view a waterfall of network requests that occurred during the recording.

Requests are color-coded as follows:

• HTML: Blue
• CSS: Purple
• JS: Yellow
• Images: Green

Click on a request to view more information about it in the Summary tab. For example, in the previous figure, the Summary tab is displaying more information about the blue request that is selected in the Network section.

A darker-blue square in the top-left of a request means it's a higher-priority request. A lighter-blue square means lower-priority. For example, in the previous figure, the blue, selected request is higher-priority, and the green one below it is lower-priority.

In the first figure below, the request for www.bing.com is represented by a line on the left, a bar in the middle with a dark portion and a light portion, and a line on the right. The second figure below shows the corresponding representation of the same request in the Timing tab of the Network tool.

Here's how these two representations map to each other:

• The left line is everything up to the Connection Start group of events, inclusive. In other words, it's everything before Request Sent, exclusive.

• The light portion of the bar is Request Sent and Waiting (TTFB).

• The dark portion of the bar is Content Download.

• The right line is essentially time spent waiting for the main thread. This isn't represented in the Timing tab.

The line-bar representation of the www.bing.com request:

The Network tool:

View memory metrics

Turn on the Memory checkbox to view memory metrics from the last recording.

DevTools displays a new Memory chart, above the Summary tab. There is also a new chart below the NET chart, called HEAP. The HEAP chart provides the same information as the JS Heap line in the Memory chart.

The colored lines on the chart map to the colored checkboxes above the chart. Clear a checkbox to hide that category from the chart.

The chart only displays the region of the recording that is currently selected. For example, in the previous figure, the Memory chart is only showing memory usage from around the 400 ms mark to the 1750 ms mark.

View the duration of a portion of a recording

When analyzing a section like Network or Main, sometimes you need a more precise estimate of how long certain events took. Hold Shift, click and hold, and drag left or right to select a portion of the recording. At the bottom of your selection, DevTools shows how long that portion took.

View a screenshot

See Capture screenshots while recording to learn how to turn on screenshots.

Hover over the Overview to view a screenshot of how the page looked during that moment of the recording. The Overview is the section that contains the CPU, FPS, and NET charts.

You can also view screenshots by selecting a frame in the Frames section. DevTools displays a small version of the screenshot in the Summary tab.

Click the thumbnail in the Summary tab to zoom in on the screenshot.

View layers information

To view advanced layers information about a frame:

1. Turn on advanced paint instrumentation.

2. Select a frame in the Frames section. DevTools displays information about the layers in the new Layers tab, next to the Event Log tab.

Hover over a layer to highlight it in the diagram.

To move the diagram:

• Select Pan Mode () to move along the X and Y axes.

• Select Rotate Mode () to rotate along the Z axis.

• Select Reset Transform () to reset the diagram to the original position.

View paint profiler

To view advanced information about a paint event:

1. Turn on.

2. Select a Paint event in the Main section.

The Paint Profiler tab:

Analyze rendering performance with the Rendering tool

Use the features of the Rendering tool to help visualize the rendering performance of your page.

To open the Rendering tool:

1. Open the Command Menu.

2. Start typing Rendering, and then select Show Rendering. DevTools displays the Rendering tool at the bottom of your DevTools window.

View frames per second in realtime with the FPS meter

The FPS meter is an overlay that appears in the top-right corner of your viewport. It provides a realtime estimate of FPS as the page runs. To open the FPS meter:

1. Open the Rendering tool. Analyze rendering performance with the Rendering tool.

2. Select the FPS Meter checkbox.

View painting events in realtime with Paint Flashing

Use Paint Flashing to get a realtime view of all paint events on the page. Whenever a part of the page gets re-painted, DevTools outlines that section in green.

To turn on Paint Flashing:

1. Open the Rendering tool. See Analyze rendering performance with the Rendering tool.

2. Select the Paint Flashing checkbox.

   

View an overlay of layers with Layer Borders

Use Layer Borders to view an overlay of layer borders and tiles on top of the page.

To turn on Layer Borders:

1. Open the Rendering tool. See Analyze rendering performance with the Rendering tool.

2. Select the Layer Borders checkbox.

See the comments in debug_colors.cc for an explanation of the color-codings.

Find scroll performance issues in realtime

Use Scrolling Performance Issues to identify elements of the page that have event listeners related to scrolling that may harm the performance of the page. DevTools outlines the potentially problematic elements in teal.

To view scroll performance issues:

1. Open the Rendering tool. See Analyze rendering performance with the Rendering tool.

2. Select the Scrolling Performance Issues checkbox.

See also:

• Slow scroll rects (checkbox) in Navigate webpage layers, z-index, and DOM using the 3D View tool.

Disable local fonts

In Rendering tool, use the Disable local fonts checkbox to emulate missing local() sources in @font-face rules.

For example, when the Rubik font is installed on your device and the @font-face src rule uses it as a local() font, Microsoft Edge uses the local font file from your device.

When Disable local fonts is selected, DevTools ignores the local() fonts and fetches each font from the network:

This feature is useful if you use two different copies of the same font during development, such as:

• A local font for your design tools.
• A web font for your code.

Use Disable local fonts to make it easier to:

• Debug and measure loading performance and optimization of web fonts.
• Verify accuracy of your CSS @font-face rules.
• Discover differences between local versions installed on your device and a web font.

Note

Portions of this page are modifications based on work created and shared by Google and used according to terms described in the Creative Commons Attribution 4.0 International License. The original page is found here and is authored by Kayce Basques (Technical Writer, Chrome DevTools & Lighthouse).

This work is licensed under a Creative Commons Attribution 4.0 International License.