data-dashboard

Skill: Data dashboard

A dashboard is the hardest screen to keep honest: it is dense, it is mostly

non-text, and almost every default makes it worse. This is the recipe that

produced examples/showcase/ and examples/terminal/, both of which pass every

gate in both themes.

1. Decide the brief before drawing anything

Answer these in one line each, or /grill-me them out of the user:

• Who reads this, and what decision do they make from it? A revenue console

for an operator and a trading desk for a dealer look nothing alike.

• What is the one number that leads? A dashboard without a lead is a wall.
• What is the update cadence? Hourly figures get a "last run" line. Live

figures get a tape and a timestamp per row.

• How dense is honest? A terminal earns 12 panels. A weekly report does not.

2. Layout sequence, not a grid of equal cards

Four equal stat cards is the single loudest tell that nobody designed this.

Compose in bands, each a different shape:

| Band | Content | Why |

|---|---|---|

| 1 | Hero metric at 3x body size + its own chart, spanning most of the width | The eye lands once |

| 2 | Two or three secondary figures, stacked or narrow | Quiet by construction |

| 3 | Three different chart shapes side by side (donut, ranked bars, sparklines) | Variety reads as intent |

| 4 | A table that really sorts, plus a feed or log | Detail after summary |

| 5 | A footer line that ends the page | A page must end on purpose |

Use a 12-column grid with explicit spans (span 8 / span 4), collapsing to 6

then 1. Never repeat(auto-fit, …) for the primary bands - it produces exactly

the equal-card wall you are avoiding.

3. The chart inventory

All of these are plain inline SVG with viewBox, sized by CSS, filled from

--color-chart-*. No chart library, no runtime dependency.

| Chart | Geometry | Use it for |

|---|---|---|

| Bar / column | <rect> per bucket, rx for a soft corner | Discrete periods |

| Candlestick | <line> wick + <rect> body per period, class by up/down | OHLC price |

| Volume | Bars under the price chart, same x-scale, opacity:.45 | Conviction behind a move |

| Moving average | <polyline> over the candles, 2px, round joins | Trend through noise |

| Line / sparkline | <polyline>, pathLength="1" for a draw animation | Trend in a cell |

| Area / stacked area | <path> per band: forward along the top, reverse along the previous baseline, close | Composition over time |

| Depth | Two cumulative area paths mirrored around the mid | Book liquidity |

| Waterfall | Floating <rect> per step + dashed connectors between levels | Attribution |

| Donut | <circle> with stroke-dasharray and rotate() per segment | Share of a whole, 3-5 slices |

| Radial gauge | Same trick, stroke-linecap:round, 270-degree sweep | One value against a limit |

| Scatter / bubble | <circle>, radius = third dimension | Two measures plus weight |

| Correlation matrix | HTML table, cell tint via color-mix | Pairwise relationships |

| Heatmap | HTML table or <rect> grid, tint by value | Cohorts, calendars |

| Order book | HTML table with a depth bar per row | Bids and asks |

Generate the geometry, do not hand-place it. Write a small deterministic

script (a seeded walk) that emits the SVG elements, then paste the output in.

Hand-typed coordinates drift and cannot be regenerated.

4. Domain correctness is part of craft

Gates cannot catch a chart that is drawn beautifully and means nothing. Check by

hand:

• A correlation matrix is symmetric and its diagonal is exactly 1. Random

values in both triangles is an instant tell to anyone who reads one for a living.

• A stacked area sums to the total; bands must not cross or leave gaps. The

usual bug is reversing the baseline by index instead of by coordinate, which

shows as dark wedges between bands.

• A waterfall needs connectors, and the closing bar must equal opening plus

the steps.

• Depth rises away from the mid on both sides; it never falls.
• A donut whose segments do not total the whole is a pie chart lying.

5. Accessibility contract, per chart

• Every SVG gets role="img" plus either aria-label or <title>+<desc>

referenced by aria-labelledby. Say what the chart shows, not that it is a

chart: "Range 182.06 to 200.10, closing at 187.84" beats "price chart".

• Never encode meaning in colour alone. Green with a + and an arrow; red with a

-. Up and down also carry a word in the table cell.

• Tables get <caption> (use .sr-only when the panel header already says it),

scope="col" / scope="row", and aria-sort only if clicking really sorts.

• Sortable headers, range tabs and theme toggles all declare state - so they must

change it on a real click. verify_interactive.mjs clicks them and checks.

6. The traps that only appear when you measure

Every one of these was found on a screen that looked finished. The first group a

gate caught; the ones marked "no gate sees it" were caught by opening the

screenshot and looking, which is why that step is not optional:

• A chart palette is not a text palette. White initials on --color-chart-4

measured 2.65:1 in dark. Chart colours are tuned for large filled shapes.

• Success green as text on a raised surface measured 4.43:1 - four

hundredths short of AA. Put the colour on the icon and the sign; keep the text

neutral.

• axe must not run mid-transition. Disable transitions before flipping the

theme, or contrast is sampled while colours are still moving.

• Dense tables do not fit a phone. Drop the column a phone can lose - the

sparkline, the derived value - in a media query, and say so in a comment. Do

not shrink type below the scale.

• Stagger comes from a token: calc(var(--duration-fast) 0.6 n), never a

typed millisecond.

• A grid row stretches its items. Two fields side by side where only one has

a hint: the hint-less control grows to match the taller column and the two

inputs end up different heights. Set align-content: start on the field and an

explicit block-size on the control. Measure the heights in the render - the

difference is obvious in a screenshot and invisible in the markup.

• The same stretch hits whole panels, and no gate sees it. A row is as tall as

its tallest panel, and the short one packs its content to the top and ends in a

bordered void - a heatmap panel with 130px of nothing under the caption, a right

column that stops two panels short of the map beside it. Every panel in a row

has to say which it is: one child absorbs the slack

(grid-template-rows:auto minmax(0,1fr), and that child's own tracks go

minmax(<min>,1fr) so its rows grow too), or the rows share it out

(align-content:space-between), or the short column earns another panel.

Screenshot the row and look at the bottom edge of each panel; this never shows

up in the markup.

• auto-fit silently drops a column, and no gate sees it. Three gauges in a

panel about 340px wide with minmax(min(100%,7rem),1fr) resolved to two tracks

and orphaned the third beside an empty cell. When the count is fixed and

meaningful, write repeat(3,minmax(0,1fr)) and give narrow widths their own rule.

• A category chart needs its categories on the page, and no gate sees it. A

Pareto of five defect types whose names live only in the aria-label is a row

of anonymous bars to everyone looking at it. Put the labels under the bars -

lay the plot out on an even pitch inside its viewBox so a matching grid of

labels lines up without a second coordinate system.

• An .sr-only needs a positioned ancestor. Inside a scroller it otherwise

resolves against the initial containing block, lands outside the viewport, and

inflates the document's scroll width by hundreds of pixels.

• A zero-area element that only has area while it animates reads as content

lost under prefers-reduced-motion. Give a radar sweep a wedge, not a 1px line.

• Never reuse a class name across layout and colour. .c4 as both a

four-column span and the fourth chart colour painted an entire panel pink.

7. The loop

node scripts/measure_render.mjs <file> && node scripts/measure_render.mjs --dark <file>
node scripts/verify_states.mjs <file>  && node scripts/axe_audit.mjs --dark <file>
node scripts/verify_responsive.mjs <file> --scale=1.25
node scripts/verify_interactive.mjs <file>
node scripts/slop_tells.mjs --strict <file> && node scripts/taste_audit.mjs --strict <file>

Then screenshot it and look, in both themes, at 1600 and 390 wide. The gates

will pass a chart that is drawn wrong. A correlation matrix that is not

symmetric is 16/16 green and still embarrassing.

Worked references, both gate-verified: examples/showcase/index.html (revenue

console) and examples/terminal/index.html (trading desk, ten chart types).