What's New In DevTools (Chrome 65)

New features coming to DevTools in Chrome 65 include:

Local Overrides

Local Overrides let you make changes in DevTools, and keep those changes across page loads. Previously, any changes that you made in DevTools would be lost when you reloaded the page. Local Overrides work for most file types, with a couple of exceptions. See Limitations.

Persisting a CSS change across page loads with Local Overrides.
Figure 1. Persisting a CSS change across page loads with Local Overrides

How it works:

  • You specify a directory where DevTools should save changes.
  • When you make changes in DevTools, DevTools saves a copy of the modified file to your directory.
  • When you reload the page, DevTools serves the local, modified file, rather than the network resource.

To set up Local Overrides:

  1. Open the Sources panel.
  2. Open the Overrides tab.

    The Overrides tab
    Figure 2. The Overrides tab

  3. Click Setup Overrides.

  4. Select which directory you want to save your changes to.
  5. At the top of your viewport, click Allow to give DevTools read and write access to the directory.
  6. Make your changes.

Limitations

  • DevTools doesn't save changes made in the DOM Tree of the Elements panel. Edit HTML in the Sources panel instead.
  • If you edit CSS in the Styles pane, and the source of that CSS is an HTML file, DevTools won't save the change. Edit the HTML file in the Sources panel instead.
  • Workspaces. DevTools automatically maps network resources to a local repository. Whenever you make a change in DevTools, that change gets saved to your local repository, too.

The Changes tab

Track changes that you make locally in DevTools via the new Changes tab.

The Changes tab
Figure 3. The Changes tab

New accessibility tools

Use the new Accessibility pane to inspect the accessibility properties of an element, and inspect the contrast ratio of text elements in the Color Picker to ensure that they're accessible to users with low-vision impairments or color-vision deficiencies.

Accessibility pane

Use the Accessibility pane on the Elements panel to investigate the accessibility properties of the currently-selected element.

The Accessibility pane shows the ARIA attributes and computed
            properties for the element that's currently selected in the DOM Tree of
            the Elements panel, as well as its position in the accessibility tree.
Figure 4. The Accessibility pane shows the ARIA attributes and computed properties for the element that's currently selected in the DOM Tree on the Elements panel, as well as its position in the accessibility tree

Check out Rob Dodson's A11ycast on labeling below to see the Accessibility pane in action.

Contrast ratio in the Color Picker

The Color Picker now shows you the contrast ratio of text elements. Increasing the contrast ratio of text elements makes your site more accessible to users with low-vision impairments or color-vision deficiencies. See Color and contrast to learn more about how contrast ratio affects accessibility.

Improving the color contrast of your text elements makes your site more usable for all users. In other words, if your text is grey with a white background, that's hard for anyone to read.

Inspecting the contrast ratio of the highlighted H1 element.
Figure 5. Inspecting the contrast ratio of the highlighted h1 element

In Figure 5, the two checkmarks next to 4.61 means that this element meets the enhanced recommended contrast ratio (AAA). If it only had one checkmark, that would mean it met the minimum recommended contrast ratio (AA).

Click Show More Show More to expand the Contrast Ratio section. The white line in the Color Spectrum box represents the boundary between colors that meet the recommended contrast ratio, and those that don't. For example, since the grey color in Figure 6 meets recommendations, that means that all of the colors below the white line also meet recommendations.

The expanded Contrast Ratio section.
Figure 6. The expanded Contrast Ratio section

The Audits panel has an automated accessibility audit for ensuring that every text element on a page has a sufficient contrast ratio.

See Run Lighthouse in Chrome DevTools, or watch the A11ycast below, to learn how to use the Audits panel to test accessibility.

New audits

Chrome 65 ships with a whole new category of SEO audits, and many new performance audits.

New SEO audits

Ensuring that your pages pass each of the audits in the new SEO category may help improve your search engine rankings.

The new SEO category of audits.
Figure 7. The new SEO category of audits

New performance audits

Chrome 65 also ships with many new performance audits:

  • JavaScript boot-up time is high
  • Uses inefficient cache policy on static assets
  • Avoids page redirects
  • Document uses plugins
  • Minify CSS
  • Minify JavaScript

Other updates

Reliable code stepping with workers and asynchronous code

Chrome 65 brings updates to the Step Into Step Into button when stepping into code that passes messages between threads, and asynchronous code. If you want the previous stepping behavior, you can use the new Step Step button, instead.

Stepping into code that passes messages between threads

When you step into code that passes messages between threads, DevTools now shows you what happens in each thread.

For example, the app in Figure 8 passes a message between the main thread and the worker thread. After stepping into the postMessage() call on the main thread, DevTools pauses in the onmessage handler in the worker thread. The onmessage handler itself posts a message back to the main thread. Stepping into that call pauses DevTools back in the main thread.

Stepping into message-passing code in Chrome 65.
Figure 8. Stepping into message-passing code in Chrome 65

When you stepped into code like this in earlier versions of Chrome, Chrome only showed you the main-thread-side of the code, as you can see in Figure 9.

Stepping into message-passing code in Chrome 63.
Figure 9. Stepping into message-passing code in Chrome 63

Stepping into asynchronous code

When stepping into asynchronous code, DevTools now assumes that you want to pause in the the asynchronous code that eventually runs.

For example, in Figure 10 after stepping into setTimeout(), DevTools runs all of the code leading up to that point behind the scenes, and then pauses in the function that's passed to setTimeout().

Stepping into asynchronous code in Chrome 65.
Figure 10. Stepping into asynchronous code in Chrome 65

When you stepped into code like this in Chrome 63, DevTools paused in code as it chronologically ran, as you can see in Figure 11.

Stepping into asynchronous code in Chrome 63.
Figure 11. Stepping into asynchronous code in Chrome 63

Multiple recordings in the Performance panel

The Performance panel now lets you temporarily save up to 5 recordings. The recordings are deleted when you close your DevTools window. See Get Started with Analyzing Runtime Performance to get comfortable with the Performance panel.

Selecting between multiple recordings in the Performance panel.
Figure 12. Selecting between multiple recordings in the Performance panel

Bonus: Automate DevTools actions with Puppeteer 1.0

Version 1.0 of Puppeteer, a browser automation tool maintained by the Chrome DevTools team, is now out. You can use Puppeteer to automate many tasks that were previously only available via DevTools, such as capturing screenshots:

const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://example.com');
  await page.screenshot({path: 'example.png'});
  await browser.close();
})();

It also has APIs for lots of generally useful automation tasks, such as generating PDFs:

const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://news.ycombinator.com', {waitUntil: 'networkidle2'});
  await page.pdf({path: 'hn.pdf', format: 'A4'});
  await browser.close();
})();

See Quick Start to learn more.

You can also use Puppeteer to expose DevTools features while browsing without ever explicitly opening DevTools. See Using DevTools Features Without Opening DevTools for an example.

A request from the DevTools team: consider Canary

If you're on Mac or Windows, please consider using Chrome Canary as your default development browser. If you report a bug or a change that you don't like while it's still in Canary, the DevTools team can address your feedback significantly faster.

Feedback

The best place to discuss any of the features or changes you see here is the google-chrome-developer-tools@googlegroups.com mailing list. You can also tweet us at @ChromeDevTools if you're short on time. If you're sure that you've encountered a bug in DevTools, please open an issue.

See the devtools-whatsnew tag for links to all previous DevTools release notes.