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