What TanStack Charts does for radial bar charts and gauges 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 ring. 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 ring.
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. "Seats used on the Team plan" works. "Radial 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="Seats used on the Team plan"
ariaDescription="18 of 25 seats are in use."
/>
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
Write each ring's value as text, in the center or at the start of the ring, so the reading never depends on the arc.
Name each ring with a label beside it, not only with its color.
In a gauge, name the bands ("Below 8%", "Above 15%") and mark their limits with ticks, rather than red and green alone.
Marks need enough contrast with the background. Check light colors from a palette against the page in light and dark mode.
Say the goal
A ring only means something against its full turn. Put the goal or the capacity in the label or the description, such as "18 of 25 seats", and in the tooltip.
Keep the track out of the tooltip
A track drawn with a second bar mark also gets focus. In the tooltip's content, pick the point of the value mark by its markId, so the keyboard user hears the value and not the track.
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 ring 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.