Eval Graphics — the chart room

Internal tooling, not a product skill. This lives in eval/design-system/ and is used by maintainers to publish eval studies. It is not a Newsjack user skill, must never be installed into skills/, and is never loaded at product runtime. Do not confuse it with the main skills folder.

You produce figures for an eval study: standalone HTML that renders the Newsjack house chart style, validated by Playwright and screenshotted to PNGs you drop into a writeup. One grammar — newsprint paper, ink, a single vermilion mark — across every figure, so a study reads like one publication.

Files you work with

• assets/colors_and_type.css — design tokens (palette, type, spacing). Never edit; always link.
• charts.css — the chart primitives (.bar-primary, .line-base, .fig, .stat, heatmap classes, masthead/section/colophon scaffold). Never edit; always link.
• chart-room.html — the specimen gallery of all 9 figure types with placeholder data. This is your copy-paste source: find the figure that fits your data, lift its block, swap the geometry and labels.
• scripts/validate.mjs — Playwright validator + screenshotter.

The grammar (non-negotiable brand rules)

These come straight from the design system. Breaking one means the figure is off-brand:

• One chroma. Vermilion #E05A47 is the only colour. The highlighted / winning series is accent; every other series is quiet grey (--c-base, #E4E0D8) or an ink wash. If you reach for a second colour, you've gone wrong. No gradients. No emoji. Ever.
• Paper, not white. Background is --nj-page #F9F8F6. Borders are the hairline rgba(26,26,26,0.10). Cards are 0-radius with a faint editorial shadow.
• Type roles. Figure titles: Newsreader italic. Axis ticks, value labels, legends, eyebrows: IBM Plex Mono, ALL CAPS, ≥0.12em tracking. Descriptive captions: DM Sans.
• Value labels float above the bar (mono, centered over the column).
• Headline figures are one consistent colour — the whole numeral and its symbol in the accent (e.g. +38%, 4.2× fully vermilion), via <span class="accent">.
• Section pattern: top hairline → mono number + lowercase-italic title (left)
  • mono subtitle (right) → content.

Accent strategy — set on <body>

data-accent	Use
winner (default)	best/highlighted series = accent, others grey. The standard comparison look.
single	comparisons go all-grey; accent is reserved for one hero mark (a donut, one bar).
mono	everything ink, no chroma — for a sober, neutral data study.

Also data-grid="on|off" (gridlines) and data-barstyle="solid|outline".

Pick the figure to fit the data

Data shape	Figure (block in chart-room.html)
Two series across a few benchmarks	FIG.01 grouped bars — the flagship
One series, ranked by category	FIG.02 single-series bars
Before → after on sparse metrics	FIG.03 dumbbell / lollipop
A value over time / scale / versions	FIG.04 line / scaling curve
Two-axis tradeoff, one point highlighted	FIG.05 scatter / quadrant
Composition / share across rows	FIG.06 100% stacked bars
One number that deserves the frame	FIG.07 donut
Model × task (or any) matrix	FIG.08 heatmap (data-driven JS)
2–4 punchy single numbers, no axes	FIG.09 big-stat callouts

How to compute geometry (filling an SVG template)

The SVGs use plain coordinates inside a viewBox. The mapping math you need:

Vertical bars (FIG.01/02). Choose a baseline yBase (value 0) and a top yTop (max value). scale = (yBase - yTop) / maxVal. For a value v: barHeight = v * scale, barY = yBase - barHeight, value label at y = barY - 12. (Specimen FIG.01: yBase=500, 100→y=120, so scale=3.8.)

Dumbbell (FIG.03). Horizontal axis from xMin (value 0) to xMax (value 100). x(v) = xMin + (v/ (maxVal)) * (xMax - xMin). Draw a .stem line from x(before) to x(after), a .dot-base at before, a .dot-primary at after.

Line (FIG.04). y(v) = yBase - v*scale; evenly space x across the points; .line-primary for focal, .line-base (dashed) for baseline; optional .area-primary polygon closes down to yBase.

Donut (FIG.07). C = 2 * π * r (specimen r=104 → C≈653.45). For percent p: dash = (p/100) * C; set stroke-dasharray="{dash} {C}" on the accent ring, transform="rotate(-90 cx cy)" so it starts at 12 o'clock.

Heatmap (FIG.08). Don't hand-place cells — edit the data, tasks, models arrays in the inline <script>. Cell alpha = 0.12 + clamp((v-min)/(max-min)) * 0.88; text flips to white above alpha 0.55. Already handles any grid size.

Big-stat (FIG.09). Pure markup: <span class="fig-num"><span class="accent"> +38</span>%</span> — wrap the whole figure (or the part that should be coloured) in .accent. Keep the numeral and its symbol the same colour.

Build process

1. Read the study's numbers (e.g. an aggregate.py printout or results.json). Decide which 1–4 figures tell the story; don't over-chart.
2. Scaffold an HTML file in the study's run folder, e.g. eval/<study>/runs/<run>/figures/<name>.html. Link the design system by relative path: <link rel="stylesheet" href="../../../../design-system/assets/colors_and_type.css"> and .../design-system/charts.css. (Count the ../ from the figure file to eval/design-system/.) Set <body data-accent="…">.
3. Lift the matching figure block(s) from chart-room.html. Recompute every coordinate from the real data using the math above. Replace category labels, value labels, series names, captions, the masthead/section text. Delete the figures you don't use.
4. Keep it honest. Label sample sizes (n=), say what the score is, don't round a tie into a win, and don't invent a series the data doesn't have. The angle-generator/meanest-editor anti-slop ethos applies to charts too.
5. Validate with Playwright (required):

   cd eval/design-system/scripts
   node validate.mjs ../../<study>/runs/<run>/figures/<name>.html --out ../../<study>/runs/<run>/figures/png
   

   All checks must pass (no JS errors, accent painted, serif applied, every figure has geometry, no empty SVGs). It writes a full-page PNG plus one crop per figure — those are your embeddable assets.
6. Eyeball the screenshot before publishing. Read the full-page PNG; confirm bars/labels line up and nothing overflows.

Worked example

For the Fable-5-vs-Opus-4.8 study (eval/fable-vs-opus/), the headline numbers (overall dim mean 4.60 vs 4.36; 67/33 head-to-head; 24 vs 7 robust wins; per- dimension deltas) map cleanly to: a FIG.01 grouped-bars of the 7 dimensions (Fable accent, Opus grey), a FIG.07 donut for the win rate, and a row of FIG.09 big-stat callouts (overall mean, robust wins, publishable rate). See eval/fable-vs-opus/runs/2026-06-09-full/figures/ for the built, validated set.

Guardrails

• Never edit assets/colors_and_type.css or charts.css to force a one-off look — if a figure needs something the system lacks, that's a design-system change, raise it, don't hack the study.
• Never add a second colour, a gradient, a drop shadow on a chart, or emoji.
• Never ship a figure that hasn't passed validate.mjs.
• Placeholder data stays clearly labelled until real numbers replace it.