design-token-bridge-mcp

Instructions

Implementation Reference

• src/tools/extract-figma.ts:37-119 (handler)

  Main handler function that extracts design tokens from Figma Variables JSON. Parses the input, resolves aliases, categorizes variables by type (COLOR, FLOAT), normalizes names, and returns a DesignTokens object with colors, spacing, and radii.

  export function extractTokensFromFigmaVariables(jsonString: string): DesignTokens {
    let data: FigmaVariablesExport;
    try {
      data = JSON.parse(jsonString);
    } catch {
      throw new Error("Invalid JSON: could not parse Figma variables export.");
    }
  
    // Handle both direct format and nested under meta.variables
    const raw = data as any;
    const variables: Record<string, FigmaVariable> =
      data.variables ?? raw.meta?.variables ?? {};
    const collections: Record<string, FigmaVariableCollection> =
      data.variableCollections ?? raw.meta?.variableCollections ?? {};
  
    if (Object.keys(variables).length === 0) {
      throw new Error("No variables found in the Figma export.");
    }
  
    // Find the default mode ID (first collection's default, or first mode)
    let defaultModeId: string | undefined;
    for (const collection of Object.values(collections)) {
      defaultModeId = collection.defaultModeId;
      break;
    }
  
    const tokens: DesignTokens = {};
    const colors: Record<string, ColorToken> = {};
    const spacing: Record<string, number> = {};
    const radii: Record<string, number> = {};
  
    for (const variable of Object.values(variables)) {
      // Resolve the value for the default mode
      const modeId =
        defaultModeId ?? Object.keys(variable.valuesByMode)[0];
      let value = variable.valuesByMode[modeId];
  
      // Resolve aliases
      value = resolveAlias(value, variables, modeId, 10);
  
      // Clean up variable name: "Colors/Primary" → "primary", "Spacing/xs" → "xs"
      const name = normalizeVariableName(variable.name);
  
      switch (variable.resolvedType) {
        case "COLOR": {
          if (isColorValue(value)) {
            const hex = figmaColorToHex(value as { r: number; g: number; b: number; a: number });
            const category = inferColorCategory(variable.name);
            colors[name] = {
              value: hex,
              ...(variable.description ? { description: variable.description } : {}),
              ...(category ? { category } : {}),
            };
          }
          break;
        }
        case "FLOAT": {
          if (typeof value === "number") {
            const lowerName = variable.name.toLowerCase();
            if (lowerName.includes("radius") || lowerName.includes("corner")) {
              radii[name] = value;
            } else {
              // Default FLOAT to spacing
              spacing[name] = value;
            }
          }
          break;
        }
        // STRING and BOOLEAN are not directly mappable to our token schema
      }
    }
  
    if (Object.keys(colors).length > 0) tokens.colors = colors;
    if (Object.keys(spacing).length > 0) tokens.spacing = spacing;
    if (Object.keys(radii).length > 0) tokens.radii = radii;
  
    const hasContent = Object.values(tokens).some((v) => v !== undefined);
    if (!hasContent) {
      throw new Error("Figma variables found but none could be mapped to design tokens.");
    }
  
    return tokens;
  }

• src/types/tokens.ts:41-48 (schema)

  Output schema defining the universal DesignTokens interface structure with colors, typography, spacing, radii, elevation, and motion properties.

  export interface DesignTokens {
    colors?: Record<string, ColorToken>;
    typography?: Record<string, TypographyToken>;
    spacing?: Record<string, number>; // px values
    radii?: Record<string, number>; // px values
    elevation?: Record<string, ElevationToken>;
    motion?: Record<string, MotionToken>;
  }

• src/tools/extract-figma.ts:7-32 (schema)

  Input schema defining Figma Variables API response shape including FigmaVariablesExport, FigmaVariable, FigmaVariableCollection, and FigmaValue types for parsing Figma's JSON format.

  interface FigmaVariablesExport {
    variables?: Record<string, FigmaVariable>;
    variableCollections?: Record<string, FigmaVariableCollection>;
  }
  
  interface FigmaVariable {
    id: string;
    name: string;
    resolvedType: "COLOR" | "FLOAT" | "STRING" | "BOOLEAN";
    valuesByMode: Record<string, FigmaValue>;
    description?: string;
  }
  
  interface FigmaVariableCollection {
    id: string;
    name: string;
    modes: { modeId: string; name: string }[];
    defaultModeId: string;
  }
  
  type FigmaValue =
    | { r: number; g: number; b: number; a: number } // COLOR
    | number // FLOAT
    | string // STRING
    | boolean // BOOLEAN
    | { type: "VARIABLE_ALIAS"; id: string }; // alias

• src/index.ts:75-94 (registration)

  Tool registration with MCP server. Defines the tool name 'extract_tokens_from_figma_variables', description, input schema (variables parameter as string), and async handler that calls extractTokensFromFigmaVariables.

  server.registerTool(
    "extract_tokens_from_figma_variables",
    {
      description:
        "Parse Figma variables export JSON and extract design tokens",
      inputSchema: {
        variables: z
          .string()
          .describe("Figma Variables REST API JSON export as a string"),
      },
    },
    async ({ variables }) => {
      try {
        const tokens = extractTokensFromFigmaVariables(variables);
        return toolResult(JSON.stringify(tokens, null, 2));
      } catch (e) {
        return errorResult(e);
      }
    }
  );

• src/tools/extract-figma.ts:121-191 (helper)

  Helper functions supporting the main handler: resolveAlias (resolves VARIABLE_ALIAS references), isColorValue (type guard for color values), figmaColorToHex (converts RGB to hex), normalizeVariableName (cleans variable names), and inferColorCategory (categorizes colors by name patterns).

  function resolveAlias(
    value: FigmaValue,
    variables: Record<string, FigmaVariable>,
    modeId: string,
    maxDepth: number
  ): FigmaValue {
    if (maxDepth <= 0) return value;
    if (
      typeof value === "object" &&
      value !== null &&
      "type" in value &&
      value.type === "VARIABLE_ALIAS"
    ) {
      const target = variables[value.id];
      if (target) {
        const targetValue =
          target.valuesByMode[modeId] ?? Object.values(target.valuesByMode)[0];
        return resolveAlias(targetValue, variables, modeId, maxDepth - 1);
      }
    }
    return value;
  }
  
  function isColorValue(value: unknown): boolean {
    return (
      typeof value === "object" &&
      value !== null &&
      "r" in value &&
      "g" in value &&
      "b" in value
    );
  }
  
  function figmaColorToHex(color: { r: number; g: number; b: number; a?: number }): string {
    // Figma colors are 0-1 float range
    const r = Math.round(color.r * 255)
      .toString(16)
      .padStart(2, "0");
    const g = Math.round(color.g * 255)
      .toString(16)
      .padStart(2, "0");
    const b = Math.round(color.b * 255)
      .toString(16)
      .padStart(2, "0");
    return `#${r}${g}${b}`.toUpperCase();
  }
  
  function normalizeVariableName(name: string): string {
    return name
      .split("/")
      .pop()! // Take last segment: "Colors/Primary" → "Primary"
      .replace(/\s+/g, "-") // Spaces to hyphens
      .replace(/([a-z])([A-Z])/g, "$1-$2") // camelCase to kebab
      .toLowerCase();
  }
  
  function inferColorCategory(
    name: string
  ): ColorToken["category"] | undefined {
    const lower = name.toLowerCase();
    if (lower.includes("primary")) return "primary";
    if (lower.includes("secondary")) return "secondary";
    if (lower.includes("tertiary")) return "tertiary";
    if (lower.includes("neutral") || lower.includes("gray") || lower.includes("grey"))
      return "neutral";
    if (lower.includes("error") || lower.includes("danger") || lower.includes("destructive"))
      return "error";
    if (lower.includes("surface")) return "surface";
    if (lower.includes("background") || lower.includes("bg")) return "background";
    return undefined;
  }