# Flint Chart > Use when the user wants to visualize data — from 'which chart should I use?' to 'render this'. Helps pick the right chart from the analytical question (comparison / trend / distribution / relationship / proportion / flow / KPI), then authors a ChartAssemblyInput and renders via the flint-chart-mcp server (Vega-Lite / ECharts / Chart.js). Transform data before Flint; style tweaks after Flint. - Skill: `fabioc-aloha/flint-chart` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add fabioc-aloha/flint-chart` - Raw SKILL.md: https://api.skillmd.com/api/skills/fabioc-aloha/flint-chart/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: fabioc-aloha (https://skillmd.com/u/fabioc-aloha) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/fabioc-aloha/flint-chart --- # flint-chart: pick, author, and render a chart ## Load the version-matched Flint language first Read `flint://agent-skill` or invoke `author_flint_chart` before authoring. That source-owned resource carries the exact semantic types, chart templates, properties, and backend boundaries for the installed MCP version. This skill adds Alex-owned framing, creative treatment selection, configured-runtime setup, and `render-verify`; it does not replace Flint's language reference. For the conceptual grammar, compiler model, data-access boundary, backend contract, rendered-demo evidence, and tagged Microsoft links, read [`references/flint-language-reference.md`](references/flint-language-reference.md). It describes the published `0.5.1` contract that Illustrator pins. Use the MCP resource, `list_chart_types`, and `list_themes` as the final authority for the runtime actually installed in the host. ## What you produce (and what you do NOT) Your output is the **spec**: the `chart_spec` and `semantic_types` of a `ChartAssemblyInput`. You reference data columns **by name**. The host passes the resulting input to `assembleVegaLite`, `assembleECharts`, or `assembleChartjs` to get a backend spec. **You write the input spec, not the output spec.** And critically: - **DO** emit `chart_spec` (chart type, channel→field mapping, properties) and `semantic_types` (field → semantic type). - **Carry the claim into a standalone chart.** Set `chart_spec.title` to the Chart Brief's Big Idea, tightened only for display, and use `subtitle` for what is measured, of whom, when, and in which units. A chart may travel without its surrounding prose; its claim must travel with it. - **Reference columns by name.** How `data` itself gets bound depends on the situation — a URL, a host-side variable, or embedded rows (see "How data gets bound"). Embedding is fine for small tables; just don't re-serialize a _large_ dataset by hand, since that risks truncation and silent value corruption and wastes tokens. - **Transform data before Flint.** If the requested chart needs aggregation, filtering, joins, pivots, derived columns, or long/wide reshaping beyond Flint's built-in static-series fold, use a coding, notebook, SQL, or data tool first. Then author the Flint spec against the transformed table. - **Style after Flint, only when needed.** Author structure in Flint. For a presentation tweak Flint does not express (a reference line, annotation, or shaded band), use the Vega-Lite escape hatch — see "Post-Flint style customization". Never feed edited Vega-Lite JSON back to `render_chart`. - **Look at what you rendered.** A chart with a collapsed scale, a merged color scale, or an empty data binding renders as a valid image that tells the wrong story — `validate_chart` cannot catch that. Load the `render-verify` skill after rendering, and always after a post-Flint Vega-Lite edit. ## Verify Flint is available before rendering Before you promise to render a chart, confirm the tools exist. If they don't, install them (or ask the user to). Failing loudly early is cheaper than authoring a spec no one can render. ### For MCP rendering (default in this skill) 1. **Check for the `flint` MCP server.** Look in your available tool inventory for `render_chart`, `compile_chart`, `validate_chart`, `list_chart_types`, or `create_chart_view`. If any of them are present, the server is registered and reachable — skip to step 4. 2. **If the tools are missing, `flint-chart-mcp` is not registered.** Ask the user to add it, or add it yourself if you can edit their workspace config. **Put the file in the right place — this is the single most common failure.** | Host | Path | Top-level key | | ---------------------------- | ----------------------------- | ------------- | | **VS Code** (workspace) | `.vscode/mcp.json` | `servers` | | Claude Code / Claude Desktop | `.mcp.json` at workspace root | `servers` | | Cursor | `.cursor/mcp.json` | `servers` | | GitHub Copilot CLI | `~/.copilot/mcp-config.json` | `mcpServers` | The schema is identical across the first three, which is exactly why the wrong path looks like it should work. **VS Code never reads a workspace-root `.mcp.json`** — and it reports no error, because it isn't parsing a broken file, it's reading no file at all. If a user says "I added the config and nothing happened," check the path before anything else. **Copilot CLI differs twice over:** different path _and_ a different top-level key (`mcpServers`, not `servers`). A `servers` block pasted there fails just as silently. Prefer telling the user to run `/mcp add` inside a CLI session and let it write the file. The path is overridable via `$COPILOT_HOME`. Always **merge** into any existing config rather than overwriting it — clobbering the file destroys whatever other servers the user had. ```jsonc // .vscode/mcp.json (VS Code) — merge with any existing "servers" map { "servers": { "flint": { "type": "stdio", "command": "node", "args": ["skills/setup-dependencies/scripts/runtime-launcher.mjs", "flint"], }, }, } ``` - `"type": "stdio"` is optional in some hosts but always declare it — omitting it makes transport-related failures harder to diagnose. - Run `setup-dependencies` once after install or update. It previews npm's configured registry and exact package set before asking to apply. - Runtime calls `node /launch.mjs flint`; it starts no npm or npx process. Missing private state routes back to setup. - Do not run version-discovery commands, pass `--registry`, edit `.npmrc`, or install these binaries globally. npm configuration is the registry authority; missing packages route back to setup. - **Hardened deployment** (only inline `data.values` accepted, no local `data.url` files): append `"--disable-file-reference"` to `args`. 3. **After adding, the host must reload for MCP servers to spawn.** VS Code: `Ctrl+Shift+P` → "Developer: Reload Window". Claude Desktop / Cursor: restart the app. 4. **Verify.** Call `list_chart_types` with `{ "backend": "vegalite" }`. If it returns the chart catalog, the server is up. 5. **If the tools still do not appear, isolate which half is broken before guessing.** The server and the client fail identically from chat. If the user has the plugin repo checked out, `node scripts/verify-install.mjs` does this in one step; otherwise probe the server yourself — pipe a handshake plus a `tools/list` into the binary over stdio and read the response. A `serverInfo` block followed by a `tools` array proves the server is healthy and the fault is config, trust, or session staleness. Then work down this list: 1. **Trust prompt.** VS Code will not start a local stdio server until you approve it. `Ctrl+Shift+P` → **MCP: List Servers** → pick `flint` → **Start**, and watch for the approval dialog. 2. **Server output.** Same menu → **Show Output**. Startup crashes surface there and nowhere else. 3. **Restart the chat session.** A window reload is not always enough — the agent's tool inventory can stay stale until the session itself restarts. 4. **HTTP transport only:** an HTTP server needs OAuth authorization after starting, which is a separate step from trust. A server can be configured and started yet still unauthorized. 6. **For deeper MCP config** — HTTP transport, allowed-host lists, deployment patterns, full CLI reference — see the canonical MCP doc: . Point the user there for anything beyond the stdio install path documented above. ### For project code integration Only needed if the user asked you to write code that **imports** `flint-chart` directly (not to render via MCP). 1. **Check the project's `package.json`** for `flint-chart` in `dependencies` or `devDependencies`. If present, skip to step 3. 2. **If missing, use the project's approved dependency workflow.** Preserve its lockfile and configured registry; never probe another registry or select a newer package version automatically. The Flint library version must match the project's approved compatibility decision. ```bash npm install --save-exact flint-chart@0.5.1 ``` Add renderer peer dependencies only through the same project dependency policy; do not use this skill to discover or upgrade their versions. 3. **Import in code:** ```ts import { assembleChartjs, assembleECharts, assembleVegaLite, } from "flint-chart"; const spec = assembleVegaLite(input); // or assembleECharts / assembleChartjs ``` ### For Python Not yet published to PyPI (as of 2026-07-24). Use the npm package or MCP server for released workflows until the Python release lands. ## When the user wants more than a spec First decide which workflow the user is asking for: - **Spec authoring only:** return a `ChartAssemblyInput` or its `semantic_types` + `chart_spec` pieces. Do not install packages or write renderer code unless asked. - **MCP chart output:** if Flint MCP tools are available, **default to `create_chart_view`** only for a Vega-Lite chart when the host supports MCP App UIs — it opens an interactive, live-rendered SVG view with a customization panel. For ECharts or Chart.js, use `render_chart` for a static artifact or `compile_chart` for backend-native JSON. `render_chart` emits SVG or PNG for Vega-Lite/ECharts and PNG only for Chart.js. Use `validate_chart` to check a spec without rendering and `list_chart_types` when you need the supported chart catalog. - **Project integration, only when the user asks for code:** add Flint to an app, notebook, script, or agentic product, install/import the library, and call an assembler in code. Keep the same `ChartAssemblyInput` contract, then let the host render the backend result. For MCP clients, the server uses an exact cache-first package: ```bash node "skills/setup-dependencies/scripts/runtime-launcher.mjs" flint ``` For JavaScript or TypeScript projects, use the approved project dependency workflow and preserve the lockfile: ```bash npm install --save-exact flint-chart@0.5.1 ``` Do not add or upgrade renderer dependencies unless the user explicitly requests project integration and approves the project's dependency changes. Then compile with the requested backend: ```ts import { assembleChartjs, assembleECharts, assembleVegaLite, } from "flint-chart"; const vegaLiteSpec = assembleVegaLite(input); const echartsOption = assembleECharts(input); const chartjsConfig = assembleChartjs(input); ``` Python support is planned for a later release. Until the PyPI package is published, use the npm package or MCP server for released workflows. ```ts interface ChartAssemblyInput { // Bound by the HOST or by you, depending on the situation (see below). data: { values: any[] } | { url: string }; semantic_types?: Record; // field → semantic type ← you write this chart_spec: { // ← you write this chartType: string; // e.g. "Scatter Plot" title?: string; // claim-bearing headline for a standalone Vega-Lite chart subtitle?: string; // measure, population, period, and units encodings: Record; // channel → { field, ... } (or array) baseSize?: { width: number; height: number }; // target layout size, default 400×320 canvasSize?: { width: number; height: number }; // optional hard ceiling on stretch chartProperties?: Record; // per-chart tuning (optional) }; options?: Record; // global layout options (rarely needed) field_display_names?: Record; // readable axis / legend labels theme_spec?: string | { extends?: string; [key: string]: any }; } ``` ## Carry the Big Idea into the chart For a standalone chart, use the Chart Brief as the source of its presentation text: - `chart_spec.title` states the finding in a concise sentence. It is not a topic label or an axis title. - `chart_spec.subtitle` supplies the reading context: measure, population, period, and units. - Omit both only when a surrounding caption already supplies the same reading, such as a sparkline in a table or a dashboard tile beneath a titled panel. Flint `0.5.1` realizes the title and subtitle in the Vega-Lite backend. When ECharts or Chart.js is the delivery target, keep the authored text with the `ChartAssemblyInput` and make it visible in the surrounding artifact after inspecting the compiled result. Do not move the claim into `theme_spec`: themes govern presentation, while title and subtitle state what the reader is meant to understand. ## Calendar Heatmap in Flint 0.5.1 Use `"Calendar Heatmap"` when the question is about daily intensity, recurrence, or gaps over a long time span. Bind `x` to a date field and `color` to the daily measure; Flint sums multiple rows from the same day into one GitHub-style week-by-week cell. Calendar Heatmap is available on the `vegalite` and `echarts` backends in the reviewed `0.5.1` runtime. For an interactive MCP App use Vega-Lite with `create_chart_view`; use `render_chart` or `compile_chart` for ECharts. It is not listed for Chart.js, so choose a standard `Heatmap` or another supported alternative there. Always call `list_chart_types` when the runtime version is unknown or has changed. ## Choose a visual theme Call `list_themes` when the audience or tone calls for a coherent house style. Use a preset ID beside `chart_spec`, for example `theme_spec: "economist"`, or load `flint-theme` for a custom or inherited ThemeSpec. ThemeSpec controls presentation and compiler behavior; it does not choose fields, aggregation, filtering, sorting, titles, or values. Flint `0.5.1` themes apply to Vega-Lite. ECharts and Chart.js ignore ThemeSpec, so do not claim cross-backend parity. For a custom system, validate the bare ThemeSpec in Theme Lab and inspect a representative chart corpus before using it in a deliverable. ## How data gets bound Use the binding mode that matches the runtime. Do not mix them. 1. **Direct MCP rendering: embed rows.** When calling `render_chart`, `compile_chart`, or `validate_chart`, the tool arguments are JSON. If the data is small or already transformed by another tool, pass it as `data: { values: [...] }`. Do not pass runtime variable names in MCP tool calls — the MCP server cannot see your local variables. 2. **Direct MCP rendering: reference a local file.** The `flint-chart-mcp` server can load `data: { url: "..." }` from local `.json`, `.csv`, or `.tsv` files. By default any local file the agent can name is readable (relative paths resolve against the working directory); a hardened deployment may reject local file references entirely via `--disable-file-reference` (or `FLINT_MCP_DISABLE_FILE_REFERENCE`), in which case pass rows inline with `data.values`. Remote URL fetching is disabled. If the data must be transformed first, use a coding/data tool to write a small prepared file, then reference that file. 3. **Generated application or notebook code: bind runtime variables.** If the user asks you to add Flint to code, write normal data-loading code first and pass a real runtime value, e.g. `data: { values: rows }`, to `assembleVegaLite`, `assembleECharts`, or `assembleChartjs`. This variable pattern is for generated code, not for MCP tool calls. For spec-only answers, return the `semantic_types` and `chart_spec` pieces and state how the host should bind data. In the worked examples below, `data` is shown as `{ values: [] }` to signal "host binds this" — focus on `chart_spec` and `semantic_types`. ## Data transformation before charting Flint is a chart compiler, not a data-wrangling layer. If the chart needs grouped totals, time buckets, filters, joins, pivots, derived ratios, or a long-form table, transform the data first with a host tool, then bind the prepared table (see "How data gets bound"). Pick semantic types and channels for the transformed columns, not for columns that no longer exist. **Sanity-read the values first — don't chart blind.** Inspect the actual data with your data tool (distinct values per category column, min/max per measure), not just the column names, and watch for: - **Embedded totals.** A category column may mix an aggregate level with its parts (e.g. `all` alongside `cage-free`/`caged`, or a `Total` region). Charting the total with its parts double-counts and flattens the parts — keep one or the other on a stacked/grouped/colored channel, not both. - **Units.** Check whether a rate is a fraction (0–1) or already a percent (0–100) before tagging it `Percentage`; don't scale twice. - **One real entity.** If your breakdown column has a single distinct value, the per-group chart collapses to one mark — the intended breakdown is likely a different column. ## Post-Flint style customization Stay at the Flint level for structure (data, chart type, channels, transforms, sizing, properties) — Flint specs stay portable and regenerate safely. Drop to backend JSON only after a valid Flint chart exists, and only for a narrow presentation change Flint does not expose (exact axis/legend/mark styling, titles, annotations, reference lines, layout polish). Never use it to change the data, chart type, field mappings, or transforms — fix those upstream. For a Vega-Lite-specific style tweak: 1. Author and validate the Flint `ChartAssemblyInput`. 2. Render or inspect the Flint chart first, when possible. 3. Call `compile_chart` with `backend: "vegalite"`. 4. Make the smallest necessary style/presentation edit to the returned Vega-Lite spec. 5. Render the edited spec in the host environment with a Vega-Lite renderer. This edited Vega-Lite spec is no longer a portable Flint spec. Do not send it to `render_chart`; use `render_chart` only for Flint `ChartAssemblyInput`. **Verification is mandatory here.** Once you leave the Flint level, the MCP server's validation no longer protects you — an edited spec can render a plausible-looking chart that is silently wrong. Load the `render-verify` skill: open the result, read its console errors, and check it against the failure catalog before declaring it done. ## Publication config preset (books, reports, exec-facing) When the render target is a book chapter, a print report, or an exec-facing document, three settings routinely need to be pinned across every chart in the artifact so the visuals read as one voice. This is a Vega-Lite `config` block you can drop into the compiled spec (via Step 3 semantic types → `compile_chart` → backend edit as described above). > **Print variant of the brand palette.** The categorical range > below (blue-800 / amber-700 / green-700 / gray-500 / red-700) is the > **print-quality variant** of the Alex ACT `chart.categorical` palette. The > **screen variant** (`#10b981` / `#0ea5e9` / `#f59e0b` / `#8b5cf6` / `#ef4444`) > lives in your project's `.github/config/brand-palette.json`. Same 5-role > semantic categorical, deeper contrast for paper. Pin this once at the top of the artifact's chart set; regenerated charts inherit it without per-chart overrides. ```json { "config": { "background": "transparent", "font": "Inter, system-ui, sans-serif", "axis": { "labelColor": "#6b7280", "titleColor": "#1f2937", "gridColor": "#e5e7eb", "labelFontSize": 12, "titleFontSize": 13 }, "title": { "color": "#1f2937", "fontSize": 18, "fontWeight": 700, "anchor": "middle" }, "range": { "category": ["#1e40af", "#b45309", "#15803d", "#6b7280", "#b91c1c"] } } } ``` **Semantic discipline in the categorical range** — the palette carries meaning across the artifact, so use each color only for its assigned role: - `#1e40af` (blue-800) — correct / principled / primary emphasis - `#b45309` (amber-700) — Composition family / warning / footer takeaway - `#15803d` (green-700) — approval / correction - `#6b7280` (gray-500) — muted / de-emphasised - `#b91c1c` (red-700) — rejection / critique / target line **Report typography scale** for the HTML surrounding the chart (not the chart itself): | Role | Style | | -------------------------- | ----------------------------------------------------------------- | | Report title | 18pt / 700 / `#1f2937` | | Section header | 14pt / 700 / `#1f2937` | | Body copy | 15-16px / `#1f2937` (text) or `#6b7280` (asides) | | REJECTED / APPROVED badges | 12pt / 700 white on red-700 or green-700, `rx="3"` 80x20 pill | Print-legibility floor for figures embedded in the artifact: 12px at a 640 viewBox is 5.93pt — the instructional minimum. For the full print-legibility grammar (formula, `data-print-role` markers, text-fits ladder), the Tailwind semantic palette, and the composition idioms (BEFORE/AFTER paired panels, numbered critique callouts, family-band abstracts, 5-Visual Rule dashboards), see the [`print-svg-style-guide`](../print-svg-style-guide/SKILL.md) skill. For the engineering discipline that emits SVGs conforming to that guide (hand-authored `.mjs` generators, `data-sha256` audit hash, dataset-first with contract tests, dataset inversion), see the [`figure-generator`](../figure-generator/SKILL.md) skill. Adapted from a published decision-analysis book's figure-authoring practice. ## Attribution Chart-selection framework (§0 below) distilled from standard visualization literature — Cole Nussbaumer Knaflic (_Storytelling with Data_), Andy Kirk (_Data Visualisation_), Stephen Few (_Show Me the Numbers_, _Information Dashboard Design_), Wexler / Shaffer / Cotgreave (_Big Book of Dashboards_). For per-chart design tips and the full 48-chart catalog, see _The Defensible Decision_ chart gallery: . For live examples of every Flint `chartType` across all backends, organized by semantic category (Bar & Column / Line & Area / Scatter & Points / Distributions / Circular & Radial / Tables & Multi-Dimensional / Maps), see the canonical Flint gallery at (swap `/vegalite` for `/echarts` or `/chartjs` to view the other backends). flint-chart itself is a Microsoft Research + IDEAS Lab (Renmin University) project — canonical docs: (getting started, API reference, architecture, chart-template extension), (MCP server deployment + full CLI), and (project home + live editor). ## Step 0 — pick the chart (when the user hasn't said which one) **Skip this step** if the user already named the chart type (e.g. "scatter of weight vs mpg"). Jump to Step 1 and author the spec. Otherwise, work down this list before choosing a `chartType`. ### 0.1 One-sentence message — the Big Idea Before choosing a chart, establish the message it should carry. **Load the `chart-big-idea` skill and run it now** — look in `.github/skills/local/chart-big-idea/SKILL.md` first (heir-installed), then `skills/chart-big-idea/SKILL.md` (baseline). It does four things this step cannot do inline: - **Reads the surrounding context first** — the prose next to the insertion point, the ticket, the section heading, prior captions — so you do not ask the user to re-articulate a claim they already wrote. - **Questions the intent** — whether the chart should exist at all, and whether the stated purpose is the real one. If the intended message and the data disagree, that surfaces here rather than after rendering. - **Elicits the Big Idea** with a three-question ladder, one question at a time, when it is not written down anywhere. - **Asks the TRADITIONAL vs INNOVATIVE style stance**, which changes the chartType you pick in §0.2. The output is a compact Chart Brief. Treat it as the constraint on everything below: §0.2 selection, §0.4 coverage, and the spec you author in Steps 1-3. **If that skill is not available**, do the compact version inline (Knaflic — _Storytelling with Data_): - What is your unique point of view? - What is at stake? - Express it as a complete sentence, not a phrase. If you cannot write the sentence, ask the user for context before drawing. "Show sales" is a phrase; "Q4 sales dropped 18% in APAC — that's where our attention should go this quarter" is a sentence. The sentence shape drives the chart choice. ### 0.2 Question → family → chart > **Deeper reference**: the [`chart-vocabulary`](../chart-vocabulary/SKILL.md) skill carries the full 7-goal × ~30-chart catalog, CSAR evaluation loop, override decision table, and 5-visual rule. Reach for it when the 7 rows below aren't enough, when evaluating an AI-suggested chart, or when the artifact will be hand-authored (not rendered via Flint). | Analytical question | Family | Primary chart | Alternates | | ------------------------------ | ------------ | ----------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Rank or compare categories? | Comparison | `Bar Chart` (2-15 items; horizontal orientation for long labels) | `Grouped Bar Chart` (2-4 series), `Stacked Bar Chart` (composition + total; use `stackMode: normalize` for 100% stacked), `Slope Chart` (before/after 2 periods), `Bar Chart` with `row`/`column` facet (many items, aka Small Multiples), `Waterfall Chart` (sequential adds/subtracts) | | Change over continuous time? | Trend | `Line Chart` | `Area Chart` (volume emphasis), `Bar Chart` + `Line Chart` combo via multi-encoding `y: ["bars", "line"]` (dual metric with different scales), `Sparkline` (in-table trend) | | How are values distributed? | Distribution | `Histogram` (one variable) | `Boxplot` (compare groups + stats), `Violin Plot` (compare + shape, Vega-Lite), `Strip Plot` (every point matters), `Density Plot` (smooth shape), `ECDF Plot` (cumulative) | | Correlation between variables? | Relationship | `Scatter Plot` | `Scatter Plot` with `size` channel (3 vars, aka Bubble), `Regression` (with fit line), `Connected Scatter Plot` (trajectory over time), `Parallel Coordinates` (many vars, ECharts) | | Part of a whole? | Proportion | `Bar Chart` (most accurate) or `Stacked Bar Chart` with `stackMode: normalize` | `Pie Chart` (**only** if one slice dominates ≥60% OR comparing to 50%), donut (use the center for a KPI) — `Donut Chart` on Vega-Lite, `Doughnut Chart` on Chart.js, `Pie Chart` + `innerRadius` on ECharts, `Treemap` (many/hierarchy, ECharts), `Sunburst Chart` (interactive hierarchy, ECharts), `Funnel Chart` (sequential stages, ECharts) | | Flow between stages? | Flow | `Sankey Diagram` (linear flow, ECharts) | `Streamgraph` (aesthetic, precision sacrificed), `Heatmap` (matrix pattern), `Chord`-like flows → use `Sankey Diagram` instead | | Progress toward a target? | KPI | `Bullet Chart` (Few's superior alternative to gauges: actual + target + qualitative ranges in one horizontal bar) | `KPI Card` (single number with delta), `Sparkline` (in-table trend), `Gauge Chart` (ECharts — reserve for high-visibility single-KPI tiles only) | ### 0.3 Anti-patterns — don't recommend - **Pie with >5 slices** — humans can't compare angles; use `Bar Chart` or `Stacked Bar Chart` with `stackMode: normalize` - **Pie without a dominant slice** — if no category is ≥60% or the story isn't "X vs the rest", use a `Bar Chart` - **Word cloud for real analysis** — position and word length distort; use `Bar Chart` of top-N terms (not in Flint; export to another tool) - **Dual-axis combo without justification** — dual axes mislead by aligning unrelated scales; consider two separate charts - **Truncated Y-axis on bars** — exaggerates differences; always start `Bar Chart` at zero (Flint does this by default; don't override) - **Streamgraph when precise values matter** — the flowing baseline sacrifices readability; use `Area Chart` instead - **Gauge over Bullet** — `Bullet Chart` packs actual + target + qualitative bands in less space with more precision - **More than 5 series on a Line Chart** — becomes a spaghetti chart; use `row`/`column` facet (Small Multiples) or highlight one series and gray out the rest ### 0.4 Flint coverage — substitutes when the ideal chart isn't native Some charts from wider visualization literature aren't in Flint's registry. Recommend the substitute, not the missing chart: | Ideal chart | Flint substitute | How | | ----------------------------------------------------------------------- | -------------------------------------------------------------- | --------------------------------------------------------------------------------------- | | Waffle Chart (10×10 grid %) | `Bar Chart` or `Stacked Bar Chart` with `stackMode: normalize` | Labeled percentage bar communicates the same "N out of 100" | | Chord Diagram (circular flows) | `Sankey Diagram` (ECharts backend) | Linear flow is easier to read anyway | | Pareto Chart (bars + cumulative %) | `Bar Chart` + `Line Chart` via multi-encoding | Sort bars descending, overlay cumulative-% line | | Beeswarm Plot (every point) | `Strip Plot` with `stepWidth`, `pointSize`, `opacity` | Jittered points instead of packed; same "every dot is real" story | | Ridgeline Plot (many densities) | `Violin Plot` with `row` facet | Density curves stacked per group | | Small Multiples | any chart with `row` or `column` encoding | Native facet support | | Word Cloud / Sentiment / NPS Gauge / Likert / Mind Map | Not in Flint's scope | Export prepared data to Power BI / Tableau / dedicated tool | | Hierarchy visualization | `"Tree"` (ECharts only) | Use `detail` for node labels, `color` for parent grouping, and `size` for values; validate the installed catalog before authoring | | Control Chart / Run Chart / Pareto / Process Capability (SPC) | Not in Flint's scope | Use a dedicated SPC / Six Sigma tool; Flint isn't built for statistical process control | | Decomposition Tree / Key Influencers / Smart Narrative (AI-Powered) | Not in Flint's scope | These are Power BI features; Flint is a chart compiler, not an analytics engine | | Table / Matrix (precise value lookup) | Use a data table (not Flint) | Stephen Few's rule — tables for lookup, graphs for pattern | This table is a **catalog** boundary: Flint does not offer these chart types. [`ascii-chart`](../ascii-chart/SKILL.md) carries a separate **medium** boundary listing forms ASCII cannot carry at all, such as pie, donut, sunburst, violin, and streamgraph, because angle and smooth curves need resolution a character cell does not have. The two lists barely overlap and are not interchangeable: a chart absent here may render fine in ASCII, and a chart Flint renders well may be impossible in ASCII. ### 0.5 When to fetch a deep reference Four reference layers, ordered by cost. Fetch the cheapest one that answers the question. **Chart selection — "which chart for which analytical question?"** Fetch [The Defensible Decision — Complete Chart Gallery](https://www.thedefensibledecision.com/gallery/chart-gallery.html) when: - The user asks about a chart not in §0.2 or §0.4 - The user asks "what other charts could work here?" - The user needs per-chart design tips (axis handling, color, labeling, accessibility) - The compact table above is ambiguous for the case at hand The gallery has 48 charts across 10 families with per-chart 💡 tips, distilled from Knaflic / Kirk / Few / Wexler. **Chart capability and language — runtime (fastest, always matches the pinned server version)** Two runtime paths that need no fetch and always reflect the actual server the user has installed: - **`list_chart_types` MCP tool** — call with `{ backend: 'vegalite' | 'echarts' | 'chartjs' }` to get the current server's chart-type catalog and encoding channels. Zero-fetch; matches whatever `flint-chart-mcp` version is pinned. - **`flint://chart-types` MCP resource** — a browsable version of the same catalog, exposed as an MCP resource for hosts that surface resources in their UI (e.g., Claude Desktop). Same data, host-native display. - **`flint://agent-skill` MCP resource** — the complete version-matched chart language and authoring contract. Prefer it over copied type and property tables. - **`list_themes` + `flint://theme-skill`** — discover preset IDs and load the version-matched ThemeSpec grammar. Illustrator's `flint-theme` skill adds the Theme Lab and visual-QA loop. Prefer these over external references when the question is "does the server I'm actually talking to render `` on ``?" They cost nothing and cannot go stale. > **0.5.x note.** The underlying library's backend-neutral recommendations, > named views, and chart transformations surface through the interactive > Vega-Lite's `create_chart_view` MCP App rather than separate tools. Use it to > explore compatible arrangements without changing the data or semantic truth > layer. ECharts and Chart.js workflows use static rendering or compilation; > headless workflows keep using §0.2 plus `list_chart_types`. **Chart capability — gallery (canonical live examples)** Fetch the canonical [Flint gallery](https://microsoft.github.io/flint-chart/#/gallery/vegalite) (maintained by the microsoft/flint-chart team; always tracks the current release) when: - You need to confirm Flint actually renders a specific `chartType` on a specific backend. Swap the trailing `/vegalite` → `/echarts` or `/chartjs` to view the same catalog for other backends. - The user is deciding between Vega-Lite vs ECharts vs Chart.js and wants to see the same chart family rendered natively on each backend. - You need a live example of a chart variant (e.g. a _faceted_ boxplot, a _dodge = local_ grouped bar, a _sparse_ streamgraph) — the gallery shows multiple named variants per `chartType`. - You want the canonical semantic grouping (Bar & Column / Line & Area / Scatter & Points / Distributions / Circular & Radial / Tables & Multi-Dimensional / Maps) that Flint itself uses to organize its chart registry. This is the authoritative reference for **what Flint actually does**; §0.2–0.4 above is the compact map, but the gallery is the source of truth for edge cases and backend-specific behavior. **Chart capability — developer documentation** Use the official [Flint documentation](https://microsoft.github.io/flint-chart/#/documentation/overview) for language design, semantics, layout, APIs, and backend architecture. Runtime resources remain authoritative for the installed server's exact vocabulary. The library documents Plotly and Excel, but the `0.5.1` MCP tool schema exposes only Vega-Lite, ECharts, and Chart.js; treat other backends as project-code integration, not MCP capability. **Rule of thumb**: Defensible Decision answers "should I use a bar or a boxplot?"; `list_chart_types` and the Flint gallery answer "will Flint's `Bar Chart` on ECharts backend do what I need?"; the deep reference (`docs/reference-*.md`) answers "what exact channels and properties does that combination support?". ### 0.6 Design principles (invoke, don't substitute for reading) Short-form pointers to the underlying literature. Invoke these when justifying a choice; read the books themselves for depth. - **Trustworthy · Accessible · Elegant** (Kirk) — check the chart against all three before shipping - **Tables for lookup, graphs for pattern** (Few) — if the user wants exact values, a data table beats any chart; use `Bar Table` (Flint) only when you want compact bars with labels - **Explanatory vs exploratory** (Knaflic) — for stakeholder communication, show the pearl, not the oyster bed; strip clutter aggressively - **Bullet > Gauge Chart** (Few) — always prefer `Bullet Chart` for KPI-vs-target; reserve `Gauge Chart` for large single-KPI tiles - **Gestalt** (Knaflic Ch. 3) — group with proximity, distinguish with color/shape, connect with lines, enclose with backgrounds - **Dashboard = one screen, no scrolling, reduce to essence** (Few — _Information Dashboard Design_) — if it doesn't fit, cut, don't scroll --- ## Step 1 — pick `chartType` Use one of the registered names **exactly**. Vega-Lite is the default and broadest backend; the table below lists each Vega-Lite chart type, the channels it accepts, and its tuning properties (see …(truncated)