# Fossui > The Fresh, Minimal Flutter UI kit. Inspired by coss.com/ui, Cal.com's design system. - **Type:** MCP server - **Install:** `agentstack add mcp-fossui-fossui` - **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior - **Seller:** [fossui](https://agentstack.voostack.com/s/fossui) - **Installs:** 0 - **Category:** [Integrations](https://agentstack.voostack.com/c/integrations) - **Latest version:** 0.1.0 - **License:** MIT - **Upstream author:** [fossui](https://github.com/fossui) - **Source:** https://github.com/fossui/fossui - **Website:** https://fossui.org ## Install ```sh agentstack add mcp-fossui-fossui ``` Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent. ## About **The Fresh, Minimal Flutter UI kit. Themed from one source. Inspired by [coss.com/ui](https://coss.com/ui), Cal.com's design system.** [](https://pub.dev/packages/fossui) [](https://pub.dev/packages/fossui) [](https://github.com/fossui/fossui) [](https://coverage.fossui.org) fossui is a set of 30+ components for developers tired of every Flutter app looking like Material. It drops into any app (`MaterialApp`, `CupertinoApp`, or a bare `WidgetsApp`) and reads its own theme first, not replacing yours. The look comes from [coss.com/ui](https://coss.com/ui), Cal.com's design system: clean, neutral, superellipse corners. One import, one theme, light and dark out of the box. > [!IMPORTANT] > Unofficial and independent. Not affiliated with or endorsed by Cal.com, Inc. > or coss.com. See [NOTICE](NOTICE) for attribution. ## Why fossui - **A look that isn't Material.** A neutral, understated aesthetic with superellipse corners, drawn from the coss/Cal.com design language. - **Framework-agnostic.** Built on `package:flutter/widgets.dart`, with no platform channels and no `FossApp` wrapper. The widgets work under any app shell. - **Reads your theme, not the other way around.** Components resolve `context.fossTheme` before falling back to Material, so they keep their look inside an existing app. - **Themed from one source.** A single `FossThemeData` holds every semantic token: color, type, radius, spacing, shadow, motion. Reskin the whole app, light and dark, in one call. - **Light on dependencies.** One runtime dependency and no bundled icon package. A worst-case app that imports nearly every component adds about 384 KB: roughly 310 KB of Dart code, which tree-shakes down to what you actually use, plus the Geist font (74 KB installed, ~35 KB over the wire). Pass your own icons through plain `Widget` slots. - **Preview-rich docs.** Every component's API doc renders a live light and dark preview, not just text, and the same preview shows on hover in your IDE. Each one states plainly what it does and does not do. - **Accessible by default.** Semantics, focus, and touch targets are built into each component. ## Install ```yaml dependencies: fossui: ^0.1.1 ``` Or from the command line: ```bash flutter pub add fossui ``` Browse the package on [pub.dev/packages/fossui](https://pub.dev/packages/fossui). ## Quick start Register the theme once, then use the widgets anywhere. ```dart import 'package:flutter/material.dart'; import 'package:fossui/fossui.dart'; void main() => runApp( MaterialApp( theme: FossThemeData.light.toThemeData(), darkTheme: FossThemeData.dark.toThemeData(), home: Scaffold( body: Center( child: FossButton( onPressed: () {}, child: const Text('Get started'), ), ), ), ), ); ``` No wrapper lock-in. `FossTheme` drops into any app, and `context.fossTheme` resolves identically under `MaterialApp`, `CupertinoApp`, or a bare `WidgetsApp`. See [`example/`](https://pub.dev/packages/fossui/example) for a runnable app. ## Theming The defaults give fossui its look, but nothing is locked. Read tokens through one accessor: ```dart final theme = context.fossTheme; final color = theme.colors.primary; final radius = theme.radii.md; ``` To reskin the app, layer a `FossThemeSpec` over a base theme. Every field is optional, and anything you leave unset keeps the default. ```dart MaterialApp( theme: FossThemeData.light.retheme( const FossThemeSpec(primary: Color(0xFF16A34A), radius: 22), ).toThemeData(), darkTheme: FossThemeData.dark.retheme( const FossThemeSpec(primary: Color(0xFF51F0A8), radius: 22), ).toThemeData(), ); ``` ## Components The library covers input, feedback, overlays, and layout: | Group | Components | | --- | --- | | Actions and input | Button, TextField, NumberField, OtpField, Select, Combobox, Checkbox, Radio, Switch, Toggle, ToggleGroup, Slider, DatePicker | | Feedback | Alert, Badge, Meter, Progress, Skeleton, Spinner, Toast, Tooltip | | Overlays | Dialog, Drawer (sheet and bottom sheet), Popover | | Layout and media | Accordion, Card, Tabs, Separator, Text, Calendar, Avatar | See the [components roadmap](https://github.com/fossui/fossui/blob/main/doc/components/roadmap.md) for what is shipped and what is planned, and the [component checklist](https://github.com/fossui/fossui/blob/main/doc/components/checklist.md) for the bar each one clears. ## Icons Icon slots accept a plain `Widget`, so any icon set works: Lucide, Material Icons, Cupertino, SVGs, or your own. The package pulls in no icon dependency of its own. Examples and docs use [Lucide](https://pub.dev/packages/lucide_icons) as the documented companion. ## Platforms With no platform channels, fossui runs anywhere Flutter does: Android, iOS, web, macOS, Windows, and Linux are all supported. ## AI-native fossui runs an MCP server so your AI coding assistant writes fossui code against the real component API instead of guessing prop names and enum values. It works with any MCP client (Claude Code, Cursor, VS Code, and more) over one endpoint: ``` https://mcp.fossui.org ``` Per-client setup and the full tool list are in the [AI-native docs](https://fossui.org/docs/ai-native). ## Blog - [Introducing fossui: a minimal Flutter UI kit](https://fossui.org/blogs/introducing-fossui) - [Migrating from Material to fossui](https://fossui.org/blogs/migrating-from-material-to-fossui) - [Minimal Flutter UI kits compared: fossui vs Material (2026)](https://fossui.org/blogs/minimal-flutter-ui-kits-compared-2026) More at [fossui.org/blogs](https://fossui.org/blogs). ## Ecosystem - Documentation: [fossui.org](https://fossui.org) - Blog: [fossui.org/blogs](https://fossui.org/blogs) - Live gallery: [play.fossui.org](https://play.fossui.org) - AI-native (MCP): [fossui.org/docs/ai-native](https://fossui.org/docs/ai-native) - Package: [pub.dev/packages/fossui](https://pub.dev/packages/fossui) ## Development This package pins its Flutter SDK with [fvm](https://fvm.app): ```bash fvm install # uses .fvmrc (Flutter 3.41.9) fvm flutter pub get fvm flutter test ``` The test suite runs on every change and holds full line coverage; browse the live report at [coverage.fossui.org](https://coverage.fossui.org). Contributions are welcome. Start with [CONTRIBUTING.md](CONTRIBUTING.md) and the [Code of Conduct](CODE_OF_CONDUCT.md). ## Acknowledgements The look and component API are drawn from [coss.com/ui](https://coss.com/ui), the Cal.com design system, with ideas from [Base UI](https://github.com/mui/base-ui) and [shadcn/ui](https://github.com/shadcn-ui/ui). Full attribution is in [NOTICE](NOTICE). ## Support If fossui is useful to you, two clicks go a long way: - ⭐ [Star fossui on GitHub](https://github.com/fossui/fossui) - 👍 [Like fossui on pub.dev](https://pub.dev/packages/fossui) - ✉️ Questions or feedback: [support@fossui.org](mailto:support@fossui.org) ## Star History [](https://star-history.com/#fossui/fossui&Date) ## Source & license This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code. - **Author:** [fossui](https://github.com/fossui) - **Source:** [fossui/fossui](https://github.com/fossui/fossui) - **License:** MIT - **Homepage:** https://fossui.org Install and usage instructions live in the source repository linked above. ## Pricing - **Free** — Free ## Security capabilities Automated source analysis of v0.1.0 — what this tool can access: - **Network access:** no - **Filesystem access:** no - **Shell / process execution:** no - **Environment & secrets:** no - **Dynamic code execution:** no *"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.* ## Versions - **0.1.0** — security scan: passed — Imported from the upstream source. ## Links - Listing page: https://agentstack.voostack.com/l/mcp-fossui-fossui - Seller: https://agentstack.voostack.com/s/fossui - Browse the marketplace: https://agentstack.voostack.com/browse --- Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.