Prompts That Build Good Tableau Viz Extensions

You're building Tableau VIZ extensions: custom mark types on a worksheet's
Marks card, not dashboard extensions. For every chart in this session:

- Declare 2 to 4 Marks card tiles. Each has an id, a display name, what it
  accepts (dimension, measure or date), whether it's required, and a
  distinct encoding-icon token. Never use the ids "detail" or "tooltip".
- Read fields by tile id with getVisualSpecificationAsync, never by column
  order. Use nativeValue for math and formattedValue for labels.
- Until every required tile is filled, show a centered message naming the
  missing tiles. Never render a blank pane.
- Re-render live on data changes and on resize. No scrollbars at any size.
  Below roughly 300px wide, drop the legend first, then labels.
- Theme from CSS variables: one accent, muted grays for everything else,
  light and dark themes. Configure dialog with accent, theme and size.
- Click a mark to select it in Tableau; click empty space to clear.
- Outside Tableau, render sample data with a small DEMO DATA badge.

Build a metric card viz extension.
Tiles: Measure (measure, required), Date (date, required).
Show the latest period's value as a big abbreviated number (1.2M, 340K),
a delta chip versus the prior period as a signed percent, green up and
red down, and a sparkline of the full trend underneath with the latest
point marked.
Empty state: "Drop a measure on Measure and a date on Date".
Config: accent, theme, number format (abbreviated, full, currency),
and whether "up" is good or bad, so cost metrics color correctly.

Build a KPI scorecard viz extension.
Tiles: Measure (measure, required, allow up to 4 fields), Date (date,
required).
One row per measure: the name, the current value, change versus prior
period, and a small trend line. Rows share one width so numbers align.
Format each number by its own magnitude. Right-align numbers with
tabular digits.
If a measure has only one period, show the value and "no prior period"
instead of a 0% change.

Build a bullet chart viz extension.
Tiles: Category (dimension, required), Value (measure, required),
Target (measure, optional).
One row per category: a dark value bar over three light qualitative
bands (poor, fair, good at 60%, 80% and 100% of target, configurable),
and a thin vertical tick at the target.
If Target is empty, hide the tick and bands and say "Add a target to
see bands" in small text.
Sort by value descending by default; config toggle for alphabetical.

Build a dumbbell chart viz extension.
Tiles: Category (dimension, required), Start (measure, required),
End (measure, required). Give Start and End the arrow-left and
arrow-right icons.
One row per category: a gray dot for Start, an accent dot for End,
joined by a line. Color the line by direction (improved vs declined,
configurable which is good). Label the gap at the end of each row.
Sort by the size of the gap, largest first.

Build a lollipop chart viz extension.
Tiles: Category (dimension, required), Value (measure, required),
Color (dimension or measure, optional).
A thin muted stem and an accent dot per category, sorted descending,
with the value labeled past the dot. Negative values extend left across
a zero line.
If Color is a dimension, use a categorical palette starting with the
accent. If it's a measure, use a light-to-accent ramp.

Build a waffle chart viz extension.
Tiles: Category (dimension, required), Value (measure, required).
A 10 by 10 grid where each cell is 1% of the total. Fill cells in
category order, largest first, colored by category. Round so the grid
always totals exactly 100 cells.
Legend: category, color and percent. Hide the legend below 300px wide.
If one category is under 0.5%, list it in the legend as "<1%" rather
than dropping it silently.

Build a Sankey diagram viz extension.
Tiles: Source (dimension, required), Middle (dimension, optional),
Target (dimension, required), Value (measure, required).
Nodes as columns, ribbons weighted by Value, colored by Source at low
opacity. Hover a ribbon to highlight it and show source, target and
value; hover a node to highlight every ribbon through it.
If Middle is empty, draw two columns. Cap at 2,000 ribbons, keeping the
largest, and note "showing top N flows" in small text when capped.

Build a ridgeline (joy plot) viz extension.
Tiles: Category (dimension, required), X Axis (measure or date,
required), Height (measure, required), Color (optional).
One filled ridge per category over a shared x axis, ridges overlapping
by a configurable amount (default 50%), category labels on the left.
Sort categories by the x position of each ridge's peak.
Config: overlap, accent, fill opacity, theme.

Build a scatter plot viz extension.
Tiles: X (measure, required), Y (measure, required), Label (dimension,
optional), Color (optional). Use the letter-x and letter-y icons.
Draw a least-squares fit line and show the slope, R squared and point
count in a small stats box. Recompute them for the selected points
when the user selects marks.
Low alpha on dots so overplotting reads as density. Label only the five
most extreme points, by distance from the fit line.

Build a data table viz extension.
Tiles: Columns (any, required, allow multiple fields).
Sticky header, right-aligned numbers with tabular digits, left-aligned
text. Click a header to sort; click again to reverse. Light row
striping in the theme's track color.
Number formatting per column from the field's own format. Show a total
row for measures, toggle in config.
Never scroll the page: if rows overflow, the table body scrolls inside
the pane and the header stays put.

Build a radial bar viz extension.
Tiles: Category (dimension, required), Value (measure, required),
Color (optional).
One concentric ring per category, each arc sweeping clockwise from 12
o'clock by its share of the largest value, longest on the outside.
Labels at the start of each ring with the value. Max 12 rings; group
the rest as "Other" and say so.

The labels overlap below 400px wide. Hide every other label under 400px,
and all labels under 250px.

Make the target tick 2px and use the theme's text color, not the accent.

When I filter to one category the chart is one huge bar. Cap bar
thickness at 28px and center the rows vertically.