What TanStack Charts does for radar charts on its own, and what you add so that everyone can read them.
What you get
A named chart. ariaLabel is required, and the chart is exposed as an image with that name. ariaDescription adds a longer description.
Keyboard navigation, on by default. Tab moves into the chart and focuses the first spoke. Arrow keys move between them, and Home and End jump to the first and the last. Enter or Space pins a sticky tooltip, and Escape closes it.
The tooltip is announced to screen readers as it changes, so a keyboard user hears the values of the focused spoke.
A visible focus ring in the theme's focus color, shown for keyboard focus only.
Reduced motion. Animated charts skip their animation when the reader has asked for less motion.
An interactive legend made of real buttons, each with a pressed state, when you use interactiveColorLegend.
What you add
A label that says what the chart shows, its unit and its period. "Online and in-store revenue by month, first half" works. "Radar chart" does not.
A visible title, and a subtitle with the unit and the period, in HTML next to the chart.
The exact values another way, when they matter: a table under the chart, behind a toggle, or a download.
A second signal besides color for every series or part.
A keyboard path for every control you add yourself, such as a series filter or a period picker.
Name and describe the chart
Keep the label short and put the takeaway in the description. Do not put every value into the name: a screen reader reads it in one breath.
<Chart
definition={definition}
ariaLabel="Online and in-store revenue by month, first half"
ariaDescription="Online revenue is higher in every month except April."
/>
Give the values as a table
A table is the most reliable way to give exact values to everyone, including people who zoom far in or print the page. Render the same array the chart reads with the kit's Table, under the chart or behind a "Show as table" switch. When the values are only an illustration, a one sentence summary is enough.
Do not rely on color
Draw each profile with a different outline as well as a different fill: a wider strokeWidth, or a fill on one and an outline only on the other.
Keep fills translucent with fillOpacity, so a profile underneath stays visible.
Name the series in a legend under the chart and in the tooltip, so the colors do not have to carry the names.
Marks need enough contrast with the background. Check light colors from a palette against the page in light and dark mode.
Say what the scale means
When the spokes are rescaled, such as to a share of the best result, put that in the subtitle and the description. A reader who hears "0.8" needs to know what it is a share of.
One stop per spoke
With focusGroupAngle, the arrow keys visit one spoke at a time, and the tooltip lists every series on it. That matches how a radar is read: one measure, then the next.
Turning the keyboard off
A static chart with no tooltip can pass keyboard: false in the second argument of defineChart, so it does not add a tab stop. Keep it on for any chart that shows values on hover: otherwise keyboard users never see them.
Check it
Tab into the chart and read every spoke with the arrow keys.
Listen to it with a screen reader.
Zoom the page to 400% and confirm the values are still there.
View it in grayscale and confirm the series are still apart.
The Accessibility guideline has the principles that apply to every chart.