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Debug tools

The debug tools available for panes contain a wide range of different features to check the quality of your page and the user experience.

You can find the debug tools for each pane by clicking the pen-and-ruler icon above it. If a debug tool is active for the current pane, a blue dot will be displayed.

When a debug tool is active, you can clear it with the "X [debug tool]" button at the top of the popup and reload it with the "re-apply" button

There are over 40 different debug tools available split into different categories, ranging from color blindness simulators to text contrast checkers to disabling CSS and JS. Do you have an idea for a useful Debug tool? Let us know.

Polypane is filled with accessibility features. We wrote a full overview on our blog: Find and fix accessibility issues with Polypane.

Quick Mouse interactions

  • Clicking the debug tool icon with your primary mouse icon will open the debug tool popup.
  • Right-clicking the debug tool icon will reload the currently selected debug tools, useful for debug tools like the color contrast checker (after changes to the page) or the chaos content debug tool to apply new random content.
  • Middle clicking the debug tool icon removes the current debug tool. Holding while middle clicking will remove the debug tools from all panes.

Hold while adding a debug tool will apply it to all panes.

Overview of all Debug tools

Polypane has over 40 Debug tools and Simulators. Below we list them all.

For more information on them inside Polypane you can hover the icon to the right of each overlay in the popup.

Debug tools

The debug tools tab contains tools that give you insight into how your page is built. It is split into four different categories: Layout, Accessibility, Content and Disable features.


Contains different tools to analyse the current layout of the page

Layout Debugging

Quickly find out if elements are where you expect them to be. This debug tool is also available as ⌘ d and you can read more about it on the Layout debugging page.

Elements that cause a horizontal scroll bar/horizontal overflow are highlighted in red, making it easy to spot them. Read more about detecting horizontal overflows.


Reachability overlays a color map to show how easy it is to reach parts of the screen. It's calibrated for the mobile device sizes in Polypane and comes in a right hand and left-hand version.

Unneeded scrollbars

Draws scrollbars on the page where they are shown on regular browsers on Windows and Linux (and Mac with an external mouse) but aren't needed.


These debug tools give you ways to assess the accessibility of a page.

Contrast checker

Polypane will go through all your text and background combinations and calculate the contrast ratio. All correct ratios are mentioned once, while failing ones are all highlighted everywhere they occur.

Hover over any of the failing ratios that have an arrow to see the suggested alternative color. You can hover over that suggested alternative color to preview it, or click it to apply the new styling and copy the suggested color to your clipboard.

Polypane uses a custom-made algorithm to determine the ratio that takes the text color, background colors, text shadow, opacities, filters and text-strokes into account when determining the contrast ratio.

Select AA or AAA to check against WCAG2 AA or WCAG2 AAA level contrast. The default is AA.

Track Focus

Get a visual highlight of the current focused element that follows the focus as you tab from element to element.

The focus order overlay shows you this information as well, but because the Track focus debug tool is dynamic it's better in handling things like focus traps and interactive pages.

While tabbing through your page you will find the role and computed name of the focused element in the bottom left corner of the pane. These are what screen readers use to determine what to read out loud so it's important to check if they are correct.

Show z-index

Show the z-indices of all visible elements, including if their ancestors have z-indices.

Target size cursor

Replaces your cursor with a square so you can measure if clickable elements are large enough and far enough apart. There are three sizes:

  • 48 by 48 pixels: uses the same dimensions and logic that Google uses for their mobile friendly test.
  • 44 by 44 pixels: uses the dimensions from WCAG 2.1 SC 2.5.5 and the Apple HIG.
  • 24 by 24 pixels: uses the dimensions and logic from WCAG 2.2 SC 2.5.8.

Elements that are too small and too close together (making tapping them hard) are detected and get a red area surrounding them indicating the space they need. Inline elements inside text content are exluded from this check, following the various specifications.

Detect small text

Detects elements that have small text: 12px for any content, and 16px for form elements (to prevent iOS from zooming in your page).

When small text is found, hover over the warning to show an explanation and click the button to increase the font size to 12 or 16 pixels (depending on the type of element) so you can preview its effects.

Text Spacing (WCAG 1.4.12)

Applies the minimum text spacing requirements from the WCAG criterion 1.4.12. Use this to check if any content is lost with these extra settings. Here are the changes it applies:

  • Line height (line spacing) to at least 1.5 times the font size;
  • Spacing following paragraphs to at least 2 times the font size;
  • Letter spacing (tracking) to at least 0.12 times the font size;
  • Word spacing to at least 0.16 times the font size.

Show roles

Highlights all elements that have a role attribute, showing both the role and the element it's applied to. This helps you verify that the used role is appropriate and applicable for a given element

Show ARIA attributes

Highlights all elements that have aria attributes and lists the attributes and their values.

A11y.css third party

A11y.css will highlight any accessibility mistakes and possible risks on your page.


Asses the content itself and the way it influences the page.

Edit content

Edit content makes the entire page editable so you can quickly try out new content and see how it looks.

Polypane automatically turns on spell checking when you're in edit content mode.


The readability debug tool will calculate how difficult each sentence on your page is. Darker, redder sentences are harder to understand while lighter, greener sentences are easier to read. We calculate this using the Automated Readability Index (ARI), which works well for most western, European languages. For pages in Arabic it uses the Automatic Arabic Readability Index (AARI).

If you know of Readability Index formulas for other languages, please contact us.

Content chaos test

Content chaos test will randomly increase or decrease text content so you can check how well your layout handles these situations. Can be used to check if you layout can handle different languages or longer and shorter content.

This debug tool has three variant: Less, More and Both. Less only shortens text (to test for languages that need less characters per word), More only lengtens text (to test for languages that need more characters per word). Both is a combination of the two with less extremes.

When active a warning icon is shown next to the pane title, and the entire pane has a red border.

Learn how to use this feature with our tutorial: How to check your site in different languages and writing modes.

Hostile CSS

Hostile CSS will set ugly styles for all your default elements so you can see how well your component styles are isolated.

Placeholdifier third party

Placeholdifier replaces all your content (text, images and videos) with placeholders, so the content of a design doesn't distract from the design itself. inbetween a wireframe and a finished site.

Audible changes

With audible changes, Polypane will sounds a beep whenever the page changes. A nice way to figure out when your page is too busy, or making changes when it does not have to.

Disable features

Turn off different features to test the resilience of your page.

Disable CSS

Disable CSS will remove all CSS from stylesheets and style attributes on your page. When active a warning icon is shown next to the pane title, and the entire pane has a red border.

Disable JS

Disable JS will disable all JavaScript on a page. This will also prevent much of Polypane's tooling from running, so when this is active a warning icon is shown next to the pane title, and the entire pane has a red border.

Disable Images

Disable Images will hide all images and background images on your page. You can use this to test your email rendering for email clients that block images or to check if your layout doesn't break when images are missing.

Hide Cursor

Hide the cursor in this pane to test keyboard accessibility without cheating.


Polypane simulates different types of impairments, permanent or situational, that lets you test your pages in different scenarios.

A note on color blindness

We simulate all 8 types of color blindness. Together they affect roughly 1 in 12 men (8%) and one in 200 women in the world.

Between the simulators ending in "*omaly" and "*opia", the "*opia" ones count as "full" color blindness for that type, while "*omaly" is a milder version.

The chosen values for the "*omaly" options are averages but people with "*omaly" color blindness can be at any place on the spectrum between no color blindness and full color blindness, so be aware of that. Additionally, it's important to realise that these simulators only simulate, and will actually differ from what any individual with a color deficiency will see. Use these simulators to make broad changes for things clearly broken, rather than making small tweaks to something you find aestetically pleasing.

For more info about the color blindness simulators, read our article Developing for color blindness with Polypane.

Red-green color blindness

The most common forms or color blindness all fall under Red-Green color blindness:





Blue-yellow color blindness

Less prevalent are Blue-yellow colorblindness. 0.02% of the worldwide population has this.



Full color blindness

Full, or near-full loss of color is incredibly rare and affects less than 0.0001% of worldwide population.



Achromatopsia (cerebral)

Visual impairments

Other visual impairments usually blur or dull someone's vision. As people get older, these become more prevalent.

Cataracts Blurs and clouds vision

Glaucoma (interactive) Blurs vision, especially around the peripheral vision. Use your cursor to bring different parts of the page into focus. The page remains interactive.

Farsightedness Makes it difficult to see details up close.

Astigmatism Blurring and ghosting of the vision in a single direction. Polypane has emulation for horizontal and vertical astigmatism.

Tunnel vision Tunnel vision is the loss of peripheral vision, leaving just the center of your vision. It has a wide range of causes, from permanent (advanced Glaucoma) to temporary (altitude sickness) to situatonal (wearing goggles). This simulation will follow your mouse cursor as a way to simulate the loss of peripheral vision.

Macular degeneration The macula is the part of the retina that is responsible for central vision. Macular degeneration is the loss of that central vision. This simulation will follow your mouse cursor as a way to simulate the loss of central vision.

CMV Retinitis causes specks in your vision and is caused by the cytomegalovirus in immunocompromised people.

Three panes in Polypane showing a website, all are covered in light specks.

Photophobia A sensitivity to light.

Bright sunshine

Colors get washed out and low contrast parts of your page become invisible when watching a screen in bright sunlight.

Dimmed Screen

Emulates a desktop screen at 40% brightness or a mobile phone with brightness turned all the way down.

Night mode

Many devices have a night mode, that lowers the blue colors and increases the red colors for a more pleasant display when there is less light.


Dyslexia affects 5 to 10% of the population worldwide, but it might be as high as 17% as not all dyslexia is diagnosed.

There is no single way to simulate dyslexia as it affects different people in different ways. Our simulator makes you aware of the reading difficulty it brings.

Add your own

Do you have an idea for a useful Debug tool? Let us know.


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