Some 8000-10000 images at commons include words like "log scale", "logarithmic" or "semilog". This indicates that this is important. I would use it quite immediately in plots where numbers vary a lot.

Automatically fixing missing and trailing commas when the user saves the page is really simple. Please keep in mind that beginners edit the Data pages manually and can easily make mistakes. The error message "Syntax error" is not very informative.

In T375677#10984757, @bvibber wrote:

There is a tracking category for failed renderings; if there are any remaining cases where that logic isn't triggering correctly because something is failing where it's not caught, by all means we want to track those down. :)

https://commons.wikimedia.org/wiki/Category:Pages_using_the_Chart_extension_with_rendering_errors

Can it also be placed into a hidden maintenance category as well? For example, in https://commons.wikimedia.org/wiki/Category:MediaWiki_software_tracking_categories .

"Stackedbar" is mentioned in the .chart specification since a week ago: https://gitlab.wikimedia.org/repos/mediawiki/services/chart-renderer/-/blob/main/docs/schemas/definition/current.json?ref_type=heads .

There is currently an undocumented but simple workaround to hide the legend. See
https://commons.wikimedia.org/wiki/Data_talk:Percentage-share_of_renewables_on_the_gross_final_energy_consumption_in_the_European_Union_since_2004.chart#c-Prototyperspective-20250606121300-%22y1%22

Here are some box plots offered by Apache ECharts:
https://echarts.apache.org/examples/en/index.html#chart-type-boxplot

Just for reference, here are the most basic scatter plots that are offered by Apache echarts:
https://echarts.apache.org/handbook/en/how-to/chart-types/scatter/basic-scatter/
It allows varied dot sizes and colors.

A "step line chart" is a feature in Apache Echart, that is achieved with the parameter step: 'start':
https://echarts.apache.org/handbook/en/how-to/chart-types/line/step-line/

Two suggestions:

1. The label "Chart definition" (e.g. used for .chart link in [[:en:Template:Chart]], or "Definition" (in the corresponding German template), is misleading for regular readers, who aren’t interested in the JSON code. I suggest "Full view", "Full-resolution view" or "Details" to highlight the main user-facing function. Just like clicking a .PNG thumbnail opens a larger image, this link should be understood as a way to explore the chart more fully. It is of interest especially when the width is limited by a container. While it also exposes image info (usage metadata) and the editable .chart code, that’s not what most users care about and shouldn’t be highlighted. In the future, this view could link to the underlying .tab data and support features like zoom and interactive curve selection, which is not at all about "definition".

To specifically control height was discussed at T376845 and T375240. But this suggestion is about aspect ratio.