Vega-Lite MCP Server

import { promises as fs } from "fs"; import path from "path"; import { fileURLToPath } from "url"; const __filename = fileURLToPath(import.meta.url); const __dirname = path.dirname(__filename); interface VegaLiteExample { name: string; description: string; category: string; spec: Record<string, unknown>; url: string; } interface ExampleResult { category: string; examples: VegaLiteExample[]; totalExamples: number; } /** * Get Vega-Lite examples by category */ export async function getExample( category: string, search?: string ): Promise<ExampleResult> { const dataPath = path.join(__dirname, "..", "data", "examples.json"); try { // Try to load examples data const data = await fs.readFile(dataPath, "utf-8"); const allExamples: VegaLiteExample[] = JSON.parse(data); // Filter by category let examples = allExamples.filter( (ex) => ex.category.toLowerCase() === category.toLowerCase() ); // Apply search filter if provided if (search) { const lowerSearch = search.toLowerCase(); examples = examples.filter( (ex) => ex.name.toLowerCase().includes(lowerSearch) || ex.description.toLowerCase().includes(lowerSearch) ); } return { category, examples, totalExamples: examples.length, }; } catch (error) { // If examples data doesn't exist yet, return fallback examples if (error instanceof Error && "code" in error && (error as any).code === "ENOENT") { return getFallbackExamples(category); } throw error; } } /** * Fallback examples for common categories */ function getFallbackExamples(category: string): ExampleResult { const fallbackExamples: Record<string, VegaLiteExample[]> = { bar: [ { name: "Simple Bar Chart", description: "A basic bar chart showing categorical data", category: "bar", url: "https://vega.github.io/vega-lite/examples/bar.html", spec: { $schema: "https://vega.github.io/schema/vega-lite/v5.json", description: "A simple bar chart with embedded data.", data: { values: [ { a: "A", b: 28 }, { a: "B", b: 55 }, { a: "C", b: 43 }, { a: "D", b: 91 }, { a: "E", b: 81 }, { a: "F", b: 53 }, { a: "G", b: 19 }, { a: "H", b: 87 }, { a: "I", b: 52 }, ], }, mark: "bar", encoding: { x: { field: "a", type: "nominal", axis: { labelAngle: 0 } }, y: { field: "b", type: "quantitative" }, }, }, }, ], line: [ { name: "Simple Line Chart", description: "A basic line chart showing a trend over time", category: "line", url: "https://vega.github.io/vega-lite/examples/line.html", spec: { $schema: "https://vega.github.io/schema/vega-lite/v5.json", description: "A simple line chart.", data: { values: [ { x: 0, y: 28 }, { x: 1, y: 55 }, { x: 2, y: 43 }, { x: 3, y: 91 }, { x: 4, y: 81 }, { x: 5, y: 53 }, ], }, mark: "line", encoding: { x: { field: "x", type: "quantitative" }, y: { field: "y", type: "quantitative" }, }, }, }, ], scatter: [ { name: "Simple Scatter Plot", description: "A basic scatter plot showing the relationship between two variables", category: "scatter", url: "https://vega.github.io/vega-lite/examples/point_2d.html", spec: { $schema: "https://vega.github.io/schema/vega-lite/v5.json", description: "A scatterplot showing body mass and flipper lengths of penguins.", data: { url: "https://vega.github.io/vega-lite/data/penguins.json", }, mark: "point", encoding: { x: { field: "Flipper Length (mm)", type: "quantitative", scale: { zero: false }, }, y: { field: "Body Mass (g)", type: "quantitative", scale: { zero: false }, }, color: { field: "Species", type: "nominal" }, }, }, }, ], }; const examples = fallbackExamples[category.toLowerCase()] || []; return { category, examples, totalExamples: examples.length, }; }