Flint ThemeSpec authoring

Create a reusable visual system for Flint charts. Translate the user's reference materials into one valid ThemeSpec that can be pasted directly into Theme Lab.

Authoritative references

Read these before authoring. When prose and source disagree, the TypeScript contract is authoritative.

• Theme guide: https://github.com/microsoft/flint-chart/blob/main/docs/theme-spec.md
• Exhaustive ThemeSpec types and allowed values: https://github.com/microsoft/flint-chart/blob/main/packages/flint-js/src/core/theme/types.ts
• Real preset implementations: https://github.com/microsoft/flint-chart/tree/main/packages/flint-js/src/core/theme/presets
• Theme Lab: https://microsoft.github.io/flint-chart/#/theme-lab

Do not invent keys. If a requested decision cannot be represented by ThemeSpec, omit it and briefly identify the unsupported decision outside the JSON only when the user asked for an explanation.

Output contract

Unless the user asks for commentary, return exactly one valid JSON object:

• Return the bare ThemeSpec, not { "theme_spec": ... } and not a complete

ChartAssemblyInput.

• Do not wrap JSON in a Markdown fence.
• Do not include comments, placeholders, ellipses, or trailing commas.
• Include a stable kebab-case id and a human-readable label.
• Include only supported fields and only decisions justified by the references.
• Omit unspecified optional fields rather than guessing.

The top-level output schema is:

{
  "extends": "optional-preset-id",
  "id": "theme-id",
  "label": "Theme label",
  "ink": {},
  "type": {},
  "structure": {},
  "marks": {},
  "labels": {},
  "legend": {},
  "dataLabels": {},
  "annotation": {},
  "furniture": [],
  "facets": {},
  "layout": {},
  "chartDefaults": {},
  "compileDefaults": {},
  "interaction": {},
  "variants": []
}

Every block except id and label may be omitted. The skeleton shows the shape, not a requirement to emit empty blocks.

Theme boundary

A theme controls presentation and compiler behavior across many charts. It may decide color, typography, surfaces, grids, axes, mark geometry, labels, legends, annotations, density, spacing, facets, and reusable chart defaults.

A theme does not choose data fields, encodings, aggregation, filtering, sorting, chart titles, or data values. Never put those decisions in a ThemeSpec. Outside chartDefaults, authored policy must not name a chart type, positional channel, mark type, field, or backend property.

Workflow

1. Inspect the supplied references. Extract recurring decisions, not isolated

decoration from one screenshot.

1. Ask only for missing decisions that materially affect the theme:

identity, required colors, typography, surface/background, density, accessibility constraints, and whether an existing Flint preset is a useful base.

1. Separate evidence into system roles:

- surfaces and text hierarchy; - categorical, sequential, diverging, and status color; - typography roles; - axes, grids, baselines, frames, and structural ink; - mark weight, corners, points, separators, and spacing; - labels, legends, annotations, facets, and layout behavior.

1. Choose standalone authoring or inheritance.
2. Author the smallest coherent spec that expresses the system.
3. Check every key and enum against types.ts.
4. Return the bare JSON object.

Choosing inheritance

Use extends when a built-in preset already supplies the intended compiler behavior and the new theme is a focused variation. Available preset IDs are:

nyt, economist, swiss, nature, mckinsey, datawrapper, powerbi, powerbi-light, pop, and cartoon.

Nested objects merge. Arrays and scalar values replace the preset value. If you replace ink.series.categorical, also consider replacing categoricalExtended; otherwise high-cardinality charts may return to the base preset's extended palette.

Use a standalone theme when the reference system does not honestly inherit a preset's layout, typography, and presentation behavior.

Schema map

Use the source contract for exhaustive nested fields and enum values. These are the authored blocks and their jobs:

High-value nested shapes

{
  "ink": {
    "surface": { "source": "house", "canvas": "#ffffff", "plot": "#ffffff", "panel": "#f5f5f5" },
    "text": { "primary": "#111111", "secondary": "#444444", "muted": "#777777", "inverse": "#ffffff" },
    "structure": { "axis": "#222222", "grid": "#dddddd", "frame": "#cccccc", "rule": "#222222", "zero": "#222222", "connector": "#888888" },
    "series": {
      "single": "#0067b8",
      "categorical": ["#0067b8", "#d83b01", "#107c10"],
      "categoricalExtended": ["#0067b8", "#d83b01", "#107c10", "#5c2d91"],
      "overflow": "#777777",
      "sequential": { "stops": ["#e8f3fb", "#0067b8"], "space": "lab", "endpointsAgainstSurface": true },
      "diverging": { "stops": ["#0067b8", "#f5f5f5", "#d83b01"], "neutral": "#f5f5f5", "space": "lab", "endpointsAgainstSurface": true },
      "status": { "positive": "#107c10", "negative": "#d83b01", "neutral": "#777777" }
    },
    "accent": "#0067b8"
  }
}

This is a shape example, not a palette recommendation. Derive actual values from the user's references.

Typography roles accept family, size, weight, style, case, and color. Allowed weights are regular, medium, semibold, and bold. Use available font families or defensible fallback stacks; do not claim a font is available merely because it appears in an image.

Presence-driven policies use omit, hairline, quiet, full, or emphasised. Density uses compact, normal, or airy. Read types.ts before using less common enums.

Translation guidance

• Map brand neutrals to surfaces, text hierarchy, and structure before mapping

accent colors to data series.

• Treat categorical colors as an ordered identity set. Keep adjacent colors

distinguishable and ensure the palette remains legible on the plot surface.

• Build sequential ramps with ordered lightness. Build diverging ramps around a

meaningful neutral. Do not use categorical arrays as numeric ramps.

• Use status colors only for semantic positive, negative, and neutral meaning.
• Preserve readable contrast for primary text, axes, labels, and values.
• Translate recurring geometry into marks; do not encode a one-off shape from

a single chart as global policy.

• Prefer semantic structure (measure versus category) over physical x/y

assumptions.

• Keep the system coherent across line, bar, area, pie, matrix, distribution,

multiseries, and faceted charts.

• Use variants only for real conditional policy and include because to state

why the adaptation exists.

Validation checklist

Before returning the JSON, verify:

• It parses as strict JSON.
• It is a bare object with id and label.
• Every top-level and nested key exists in types.ts.
• Every enum value and value type matches the source contract.
• It contains no chart data, fields, encodings, titles, or backend JSON.
• Text and structural ink remain readable against their surfaces.
• Categorical colors are distinguishable; ramps have ordered lightness and

usable endpoints.

• Inherited arrays are intentionally replaced.
• The theme expresses reusable rules rather than one chart's decoration.
• The result can be pasted directly into Flint Theme Lab.