gomukit

Prebuilt, parameterized, interactive HTML widgets for MCP Apps — in Go, out of the box.

gomukit lets an MCP server ship CRUD-style UI — data tables, card carousels,
forms — as fully self-contained HTML template resources: inline CSS, inline JavaScript,
zero external files, everything embedded in your single Go binary. Widgets
speak the official MCP Apps extension (io.modelcontextprotocol/ui, spec
2026-01-26) and render in any compliant host (Claude, ChatGPT, VS Code,
Cursor, Goose, Postman, …).

Status: pre-release. APIs are not stable yet.

_{Table and Form widgets rendered by the examples/harness fake host — light and host dark themes.}

_{CardList lays a collection out as a horizontally scrolling card carousel that fits a narrow chat pane (same filter/sort/pagination/selection as Table); Card renders a single record.}

Quickstart

package main

import (
    "context"
    "net/http"

    "github.com/modelcontextprotocol/go-sdk/mcp"
    "github.com/techthos/gomukit"
    "github.com/techthos/gomukit/gosdk"
)

func main() {
    table := &gomukit.Table{
        URI:   "ui://myapp/users",
        Title: "Users",
        Columns: []gomukit.Column{
            gomukit.Text("name", "Name"),
            gomukit.Number("balance", "Balance", "currency:EUR"),
            gomukit.Badge("status", "Status", map[string]gomukit.BadgeVariant{
                "active": gomukit.BadgeSuccess,
            }),
        },
        Filterable: true,
        PageSize:   10,
    }

    server := mcp.NewServer(&mcp.Implementation{Name: "myapp"}, gosdk.EnableUI(nil))

    type in struct{}
    type out struct {
        Rows []map[string]any `json:"rows"`
    }
    gosdk.AddWidgetToolFor(server, table,
        &mcp.Tool{Name: "list_users", Description: "List users in a table."},
        func(context.Context, *mcp.CallToolRequest, in) (*mcp.CallToolResult, out, error) {
            rows, _ := gomukit.RowsOf(loadUsers())
            return nil, out{Rows: rows}, nil
        })

    h := mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server { return server }, nil)
    http.ListenAndServe(":8080", h)
}

Ask a connected assistant to "list the users" and it renders an interactive,
host-themed table — sortable, filterable, paginated — inside the chat.

Features

• Table: typed columns (text/number/date/badge/link/actions), client-side
  sort/filter/pagination, row selection with bulk actions, per-row actions →
  MCP tool calls, inline destructive-action confirmation, empty/loading states.
• Form: 11 field types, native + inline client validation, submit as a
  tool call, server-side field errors mapped inline, prefill for edit flows.
• DatePicker: a date or a range, as a widget of its own or as a form field.
  One calendar either way: bounded windows, blocked days, quick-range presets,
  ISO week numbers, month/year travel, full keyboard control.
• Menu: a launcher grid of tiles, one per UI-backed tool — the app's front
  door. Choosing a tile calls that tool so the host opens its widget.
• Host-aware theming: --gomu-* design tokens defaulting to
  host-injected CSS variables (Claude/ChatGPT look automatic), Theme struct
  overrides, dark mode.
• Locale-aware: numbers/dates formatted via Intl with the host's
  locale and time zone.
• SDK-agnostic core + adapter for the official
  go-sdk; the core works
  with any Go MCP implementation.
• Self-contained by construction: documents satisfy the spec's default
  locked-down CSP; no CDN, no network, no files on disk.

Documentation

• Widget reference — Table, Form, Card, CardList, Menu, Confirm, Choice, DatePicker, actions, data contract
• Theming — tokens, host variables, dark mode
• Architecture — rendering model, runtime, security
• Preview server — every widget as real MCP tools, for inspectors

Examples

• examples/demo — complete MCP server (streamable HTTP or -stdio):
  list/edit/save/delete/archive users, and book a follow-up call on a date
  picker whose free days are computed per call. Point MCPJam or any MCP Apps
  host at http://localhost:8080/mcp.
• examples/preview — the widest MCP server: a small app with mutable state
  (customers, orders, forms, confirmations, choices) plus a gallery of every
  widget variant as its own tool. Built for driving from an MCP Apps capable
  inspector. make preview, then point the inspector at
  http://localhost:8081/mcp. See docs/preview.md.
• examples/harness — a fake MCP Apps host in one HTML page, with a story
  browser: pick a widget variant from the rail (table, cardlist, card, form,
  menu, plus empty and long-list states), see it rendered in a sandboxed
  iframe at any viewport width, and watch the JSON-RPC traffic. It answers the
  handshake, replies to tool calls, and simulates tool results/errors and
  theme changes. go run ./examples/harness, open http://localhost:8090.

Both of the last two run from one container image, so the widgets can be put
on a URL for other people to try in their own chat client:

curl -O https://raw.githubusercontent.com/Techthos/gomukit/main/examples/docker-compose.yml
docker compose up -d      # harness on :8090, preview MCP on :8081/mcp

The preview service runs with -sandbox, which gives every MCP session its
own copy of the scenario data: visitors can use every writing tool, and no
one's edits reach anyone else. See
docs/preview.md.

Development

The TypeScript/CSS runtime lives in ui/ and is bundled with esbuild into
internal/assets/dist/ (committed, go:embed-ed — consumers never need
Node).

make assets       # npm ci + build the runtime bundle
make test         # go test ./... + vitest
make verify-dist  # fail if committed dist doesn't match ui/ sources
make build        # build the example servers into ./bin

Golden-file tests: go test ./ -update regenerates testdata/golden/.

License

MIT