Performance features reference

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

See Get Started With Analyzing Runtime Performance for a guided tutorial on how to analyze a page's performance using Chrome DevTools.

# Record performance

# Record runtime performance

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

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

2. Click the Performance tab in DevTools.

3. Click Record .

   

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's loading, as opposed to running.

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

2. Open the Performance panel of DevTools.

3. Click Start profiling and reload page . DevTools first navigates to about:blank to clear any remaining screenshots and traces. Then DevTools records performance metrics while the page reloads 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.

In the example above, the Performance panel shows the activity during a page load.

# Capture screenshots while recording

Enable the Screenshots checkbox to capture a screenshot of every frame while recording.

See View a screenshot to learn how to interact with screenshots.

# 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. Enable the Disable JavaScript Samples checkbox.
3. Take a recording of the page.

The following screenshots 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.

The example above shows a recording with disabled JS samples.

The example above shows a recording with enabled JS samples.

# 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 your computer's capabilities. For example, the 2x slowdown option makes your CPU operate 2 times slower than its usual ability. DevTools can't truly simulate the CPUs of mobile devices, because the architecture of mobile devices is very different from that of desktops and laptops.

# Enable 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 checkbox.

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

# Emulate hardware concurrency

To test application performance with different numbers of processor cores, you can configure the value reported by the navigator.hardwareConcurrency property. Some applications use this property to control the degree of parallelism of their application, for example, to control Emscripten pthread pool size.

To emulate hardware concurrency:

1. Open the Capture settings menu. See Show recording settings.
2. Check Hardware concurrency and set the number of cores in the text box.

DevTools displays a warning icon next to the Performance tab to remind you that hardware concurrency emulation is enabled.

To revert to the default value of 10, click the Revert button.

# Save a recording

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

# Load a recording

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

# Clear the previous recording

After making a recording, press Clear recording to clear that recording from the Performance panel.

# Analyze a performance recording

After you record runtime performance or record load performance, the Performance panel 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. Click on 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 its 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 Command+F (Mac) or Control+F (Windows, Linux) to open the search box at the bottom of the Performance panel.

The example above shows a RegEx pattern in the search box at the bottom of the window that finds any activity that begins with E.

To navigate activities that match your query:

• Use the Previous and Next buttons.
• Press Shift+Enter to select the previous or Enter to select the next.

To modify query settings:

• Press Case sensitive to make the query case sensitive.
• Press Regex to use a regular expression in your query.

To hide the search box, press Cancel.

# View main thread activity

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

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

The example above shows more information about the Me function call event in the Summary tab.

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.

The example above shows a flame chart in the Main section.

A click event caused a function call in script_foot_closure.js on line 53. Below Function Call you see that an anonymous function was called. That anonymous function then called Me(), which then called Se(), and so on.

DevTools assigns scripts random colors. In the example above, function calls from one script are colored light green. Calls 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.

See Disable JavaScript samples if you want to hide the detailed flame chart of JavaScript calls. When JS samples are disabled, you only see high-level events such as Event (click) and Function Call (script_foot_closure.js:53).

# 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:

• When you want to view the root activities that cause the most work, use the Call Tree tab.
• When you want to view the activities where the most time was directly spent, use the Bottom-Up tab.
• When you want to view the activities in the order in which they occurred during the recording, use the Event Log tab.

Each tabular view in the Performance panel shows links for activities such as functions calls. To help you debug, DevTools finds the corresponding function declarations in source files. Additionally, if the appropriate source maps are present and enabled, DevTools automatically finds the original files.

Click a link to open a source file in the Sources panel.

# Root activities

Here's an explanation of the root activities concept that's mentioned in the Call Tree tab, Bottom-Up tab, and Event Log sections.

Root activities are those which cause the browser to do some work. For example, when you click a page, the browser fires an Event activity as the root activity. That Event might cause a handler to execute, and so on.

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

See The Call Tree tab for an example of root activities.

# The Call Tree 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 example above, the top-level of items in the Activity column, such as Event, Paint, and Composite Layers are root activities. The nesting represents the call stack. For example, in the example above, Event caused Function Call, which caused button.addEventListener, which caused b, and so on.

Self Time represents the time directly spent in that activity. Total Time represents the time spent in that activity or any of its 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 shows you which children of the selected activity took the longest time to execute.

# The Bottom-Up 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 example above, you can see that almost all of the time was spent executing the three calls to wait(). Accordingly, the top activity in the Bottom-Up tab is wait. In the flame chart, the yellow below the calls to wait are actually thousands of Minor GC calls. Accordingly, you can see that in the Bottom-Up tab, the next most expensive activity is Minor GC.

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

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

# 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 1573.0 ms for the selected item in the example above means that activity started 1573 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 its 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 interactions

View user interactions on the Interactions track to track down potential responsiveness issues.

To view interactions:

1. Open DevTools, for example, on this demo page.
2. Open the Performance panel and start a recording.
3. Click an element (coffee) and stop the recording.
4. Find the Interactions track in the timeline.

In the example above, the Interactions track shows two interactions. Both have the same IDs, indicating that the interactions are triggered by the same user action.

# View GPU activity

View GPU activity in the GPU section.

# View raster activity

View raster activity in the Raster section.

# 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 real time estimate of FPS as the page runs. See View frames per second in real time 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.

The example above shows a tooltip when you hover over a frame.

The Frames section can show four types of frames:

1. Idle frame (white). No changes.
2. Frame (green). Rendered as expected and in time.
3. Partially presented frame (yellow with a sparse wide dash-line pattern). Chrome did its best to render at least some visual updates in time. For example, in case the work of the main thread of the renderer process (canvas animation) is late but the compositor thread (scrolling) is in time.
4. Dropped frame (red with a dense solid-line pattern). Chrome can't render the frame in reasonable time.

The example above shows a tooltip when you hover over a partially presented frame.

Click on a frame to view even more information about the frame in the Summary tab. 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. In the example above, the Summary tab is displaying more information about the blue request that's 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. In the example above, the selected request is higher-priority, and the green one above it is lower-priority.

In the example above, the request for www.google.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 screenshot below shows the corresponding representation of the same request in the Timing tab of the Network panel. 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 is not represented in the Timing tab.

The example above shows the line-bar representation of the www.google.com request.

The example above shows the Timing tab representation of the www.google.com request.

# View memory metrics

Enable the Memory checkbox to view memory metrics from the last recording.

DevTools displays a new Memory chart, above the Summary tab. There's 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 example above shows memory metrics above the Summary tab.

The colored lines on the chart map to the colored checkboxes above the chart. Disable 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 example above, the Memory chart shows only the memory usage for the start of the recording, up to around the 1000ms 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.

In the example above, the 488.53ms timestamp at the bottom of the selected portion indicates how long that portion took.

# View a screenshot

See Capture screenshots while recording to learn how to enable 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 clicking a frame in the Frames section. DevTools displays a small version of the screenshot in the Summary tab.

The example above shows the screenshot for the 195.5ms frame in the Summary tab when you click on it in the Frames section.

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

The example above shows a zoomed-in screenshot after you click its thumbnail in the Summary tab.

# View layers information

To view advanced layers information about a frame:

1. Enable advanced paint instrumentation.
2. Select a frame in the Frames section. DevTools displays information about its layers in the new Layers tab, next to the Event Log tab.

Hover over a layer to highlight it in the diagram.

The example above shows the layer #39 highlighted as you hover over it.

To move the diagram:

• Click Pan Mode to move along the X and Y axes.
• Click Rotate Mode to rotate along the Z axis.
• Click Reset Transform to reset the diagram to its original position.

See layer analysis in action:

# View paint profiler

To view advanced information about a paint event:

1. Enable advanced paint instrumentation.
2. Select a Paint event in the Main section.

# Analyze rendering performance with the Rendering tab

Use the Rendering tab's features to help visualize your page's rendering performance.

Open the Rendering tab.

# View frames per second in real time with the FPS meter

The Frame rendering stats is an overlay that appears in the top-right corner of your viewport. It provides a real time estimate of FPS as the page runs.

See Frame rendering stats.

# View painting events in real time with Paint Flashing

Use Paint Flashing to get a real time view of all paint events on the page.

See Paint flashing.

# 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.

See Layer borders.

# Find scroll performance issues in real time

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.

See Scrolling performance issues.