🍋 Limoni
A terminal UI engine for Go that tests can click, AI agents can drive,
and the garbage collector never sees.
English • Türkçe
▶ Try it in your browser — the same engine compiled to WebAssembly, no install.
Only what changed is sent: go run ./examples/xray lights up every cell the diff writes.
---
## Quick start
```bash
go get github.com/thebanri/limoni
```
```go
package main
import "github.com/thebanri/limoni"
func main() {
limoni.Run(func(f *limoni.Frame, ev *limoni.Event) bool {
if ev != nil && ev.Type == limoni.EventKey && ev.Key.Type == limoni.KeyEsc {
return false // quit
}
f.RenderWidget(limoni.Border(
limoni.Center(limoni.Label("Hello from Limoni 🍋 (Esc quits)", limoni.Bold())),
limoni.SymbolsRounded,
limoni.Fg(limoni.Hex("#FFCC00")),
), f.Area())
return true
})
}
```
Or generate a project that runs straight away, with a test already written:
```bash
go run github.com/thebanri/limoni/cmd/limoni@latest new myapp # -template counter|dashboard|form|chat|ssh
cd myapp && go mod tidy && go run .
go test ./... # a uitest test comes with every template
```
**Next:** [Getting started](docs/getting-started.md) · [Widget gallery](docs/widget-gallery.md) · [Examples](#examples)
---
## Why Limoni
### 1. Your TUI has a semantic tree, so tests and agents address widgets by name
Most terminal automation, such as [termwright](https://github.com/fcoury/termwright) or
[mcp-tui-test](https://github.com/GeorgePearse/mcp-tui-test), parses the rendered character
grid, so a test breaks when the layout moves by one column. A Limoni app builds a
semantic tree every frame (the same tree a screen reader uses), and the tools below
work on that tree instead.
**`uitest`: Playwright-style tests.** Checks wait instead of sleeping, and a failure
prints the whole tree of the last frame.
```go
page := uitest.Run(t, 80, 24, app.draw) // in process: no terminal needed
page.GetByRole("input", "New task").Type("Tag v1.0")
page.GetByRole("button", "Add task").Click()
page.Expect(page.GetByRole("list-item", "").Within(page.GetByRole("list", "Tasks"))).ToHaveCount(3)
page.Expect(page.GetByID("status")).ToContainLabel("Added")
```
**`limoni-mcp`: let an AI agent drive the app.** It gives Claude Code, Cursor or any
MCP client eight tools (`tree`, `click`, `type_text`, `wait_for`…) that work on the
same tree. In one recorded run, Claude Code completed a release checklist in 17 tool
calls. That run included typing a deploy token the agent could not read back.
```bash
go run -tags limoni_debug ./examples/agent_checklist
claude mcp add limoni -- limoni-mcp -socket "$XDG_RUNTIME_DIR/limoni-checklist.sock"
```
The automation socket only exists in `-tags limoni_debug` builds. It is closed by
default, only the same user can connect, and secret fields are never exposed.
→ [Semantic automation, MCP and uitest](docs/automation.md)
### 2. Fast where you can feel it
- **Zero heap allocations per frame** for the renderer, every widget's drawing, and the click handling of the common input widgets, enforced in CI, so animations don't stutter from GC pauses. That includes widgets that drag or call your code — Table, Slider, Dialog, TreeView, CommandPalette — once their state is attached. [The details](docs/architecture.md#5-allocation-free-interactive-frames).
- **Few bytes per frame.** Blank runs become `ECH`/`EL` and repeats become `REP`: a full-screen redraw is **377 bytes**, and an idle app sends **nothing**. Bytes, not CPU, are what you feel over SSH.
- **Virtual tables and lists.** One million rows scroll at ~2.7 ms a frame, because only visible rows are touched.
| Measured on a Ryzen 5 5600, Go 1.27.1 | Latency | Allocations |
| :--- | ---: | ---: |
| Full-screen diff, 120×40, every cell changed | ~50 µs | 0 |
| 10% of the screen changed | ~11 µs | 0 |
| Nothing changed | ~2 ns | 0 |
| 100 layered blocks, drawn and diffed | ~68 µs | 0 |
Absolute numbers depend on the machine. The comparisons against Ratatui 0.30.2,
Ultraviolet and Bubble Tea v1.3.10, including which ratios are *not* meaningful, are in
[docs/benchmarks.md](docs/benchmarks.md) and the [methodology](docs/benchmark-methodology.md).
One earlier run showed a 4,700× lead; it came from a bug in the benchmark harness,
and the [methodology](docs/benchmark-methodology.md#the-4700-that-was-a-harness-bug) explains how it was caught.
### 3. Batteries that other TUI libraries leave to you
| | |
| :--- | :--- |
| 🕶️ **3D** | A software rasteriser for OBJ/STL/PLY/GLB with Lambert and Gouraud shading, drawn in terminal cells |
| 🖼️ **Images** | Kitty, Sixel, iTerm2 and half-block fallback |
| 📊 **Charts** | Braille line charts, bar charts, pie charts, sparklines |
| 📝 **Markdown** | Headings, lists (nested, numbered, tasks), quotes, tables, links, and fenced code highlighted by language — including a block still streaming in |
| ♿ **Accessibility** | A semantic tree, a screen-reader line mode, `NO_COLOR`, high contrast, reduced motion |
| 🧬 **Unicode** | UAX #29 grapheme clusters (Unicode 17.0, all 766 conformance tests), so flags and emoji families take one cell |
| 🔗 **Hyperlinks** | OSC 8 links, in markdown or any style — and where the terminal cannot show them, the address is printed instead |
| 📃 **Inline mode** | Render in a band of the normal screen, like `gum`, with scrollback intact |
| ⏺️ **Session replay** | Record a session, replay it as a regression test ([docs](docs/session-recording.md)) |
| 🌐 **Everywhere** | Linux, macOS, BSD, Windows, WebAssembly in the browser, SSH sessions |
The only dependencies are `golang.org/x/sys` and `golang.org/x/crypto`.
 |
 |
go run ./examples/treeview |
go run ./examples/charts |
### Is Limoni the right choice?
**Pick Limoni if** you are writing a terminal app in Go and any of these matter:
- **You want to test the UI, or let an AI agent use it**, by widget role and label
rather than by screen coordinates (`uitest`, `limoni-mcp`).
- **It redraws a lot**: dashboards, log viewers, monitoring, games, animation,
anything over SSH. The draw path makes no garbage and sends few bytes.
- **It needs things other libraries leave to you**: 3D models, images, charts,
markdown, a million-row table, screen-reader support, WebAssembly in the browser.
- **You want both styles in one library**: immediate mode (`limoni.Run`) for
dashboards, the Elm architecture (`limoni.RunProgram`) for forms and wizards.
- **You want a small dependency tree**: `golang.org/x/sys` and `golang.org/x/crypto`.
**Pick something else if:**
- You need a **stable 1.0 API** today. Limoni is pre-1.0 (see [Status](#status)).
- You rely on the **Charm ecosystem** (Bubbles, Huh, Glamour, Wish) and its
community. Bubble Tea is the larger and older project. If you already have a
Bubble Tea app, `compat/bubbletea` runs your models on Limoni
([migration guide](docs/bubbletea-migration.md)), so you can try it without a rewrite.
- You are writing **Rust**: use Ratatui.
- The app is a **one-shot prompt** (a single question, a spinner): a small prompt
library is less to learn.
A feature-by-feature table against Bubble Tea v1/v2 and Ratatui 0.30 is in
[docs/comparison.md](docs/comparison.md).
---
## Built with Limoni: zest
[**zest**](cmd/zest) is a log viewer and Limoni's flagship app. It follows files and pipes, colours by
level, and filters a million lines without stalling. A 67 MiB, 1,000,000-line log is on screen in about half
a second.
```bash
go install github.com/thebanri/limoni/cmd/zest@latest
zest -demo 1000000 # or: zest app.log, kubectl logs -f pod | zest
```
Or [try it in the browser](https://thebanri.github.io/limoni/): the "Logs · zest" scene.
### And: globe
[**globe**](apps/globe) is a world you can turn, search, zoom into and pin — and what a Limoni
application looks like from the outside, since it is a module of its own that depends on a
published Limoni and uses nothing but its public API.
```bash
go install github.com/thebanri/limoni/apps/globe@latest
globe -at Türkiye
```
`go install` puts the binary in `$(go env GOPATH)/bin` — `~/go/bin` unless you changed it —
which a fresh Go install does not add to your `PATH`. If `globe` is "command not found", add
that directory to `PATH` or run `~/go/bin/globe`.
Everything on it is in the semantic tree, so "find Turkey on the world map" is something an agent
can do over MCP: type into `search`, click the row, read `image#globe` back as
`value="39.3°N 34.5°E · zoom 2.6×"`. Nothing of it reaches you when you import Limoni — a
directory with its own `go.mod` is not part of the module around it.
### And your shell: backdrop-shell
[**backdrop-shell**](apps/backdrop-shell) puts a moving scene behind your shell, in any terminal —
an aurora, a night city, a starfield, a synthwave sunset, a picture, or ASCII art of your own that
blinks or drifts. The text in front stays sharp, selecting copies only what the shell wrote, a
narrower window keeps every line, and the opacity or the scene changes at once in every open
terminal. It costs about half a percent of one core, and nothing while the window is in the
background.
```bash
curl -fsSL https://raw.githubusercontent.com/thebanri/limoni/main/apps/backdrop-shell/install.sh | sh
backdrop-shell opacity 0.3 # quieter, in every open terminal
backdrop-shell enable -scene synthwave # or -image wall.jpg, or -art my-art.txt
```
Drawing and animating your own: [docs/backdrop-art.md](docs/backdrop-art.md). The same scenes go
behind any Limoni application with `limoni.WithBackdrop(backdrop.Aurora())`.
### And some games
[**Lemon Drop**](apps/lemondrop) is falling blocks where a piece that lands crumbles into sand of its colour.
A run of one colour that reaches from wall to wall is the line: it flashes and goes, and what rested on it
falls, sometimes into the next one.
```bash
go install github.com/thebanri/limoni/apps/lemondrop@latest
lemondrop
```
Or [play it in the browser](https://thebanri.github.io/limoni/?app=lemondrop), with sound and a
world leaderboard.
[**Lemon Snake**](apps/lemonsnake) is a snake that eats lemons. Every five, a monster climbs out of the far
corner and hunts the head; spit the seeds your lemons bring at it, and where it steps on
the body it bites the rest off. Every level is faster, and so is its monster; fill the board to win. `t` switches between five
colour themes at any time. It glides in half-block pixels, plays soft synthesised sounds, and
sends finished runs to the same shared leaderboard as Lemon Drop.
```bash
go install github.com/thebanri/limoni/apps/lemonsnake@latest
lemonsnake
```
Or [play it in the browser](https://thebanri.github.io/limoni/?app=lemonsnake), with its sound and the
world leaderboard.
[**Lemon Sweep**](apps/lemonsweep) is a first-person roguelite in a terminal made of terminals: the walls
are a shell, a log viewer, some Go and htop. You are the garbage collector, and Bubble Tea, Ratatui, tview,
Ink and ncurses have come for the heap, each drawn the way its own apps look: pink rounded boxes and
spinners, Ferris, double-lined modals that split into their buttons, `` that splits in two. Aim with
the mouse (an empty heap reloads by itself), and take an augment card every level; once every card held
is at its last rank, a level is a random stat. Shots that split, bounce, explode and arc multiply each
other into something broken, and the RECIPES book says which cards do.
Pick one of four maps on the title: a mini-boss comes every two minutes, a boss every two and a half, and
the map's warden at ten; if it stands, the pressure builds (armour, insulation, speed), and no build holds
it for long. Experience hangs in the air until you walk over it, and a corner is no place to hide. There is
no leaderboard: records stay on the machine, or in the browser.
```bash
go install github.com/thebanri/limoni/apps/lemonsweep@latest
lemonsweep
```
`command not found`? `go install` puts programs in `$(go env GOPATH)/bin`, usually `~/go/bin`, which
macOS does not put on the `PATH`. Run `~/go/bin/lemonsweep`, or add
`export PATH="$PATH:$(go env GOPATH)/bin"` to `~/.zshrc` and open a new terminal.
Or [play it in the browser](https://thebanri.github.io/limoni/?app=lemonsweep), where the pointer is locked
for mouse look. A frame allocates nothing, the most broken build's full pools included.
[**pikap**](apps/pikap) is a record player drawn in half blocks (or ASCII). It follows whatever the computer is playing
(Spotify, a browser tab, mpv, anything on MPRIS): the cover turns on the record and the tonearm moves
across it. Dragging the record or the arm moves the song back and forth. Given files, it plays them
itself, and then pausing slows the music down with the platter and dragging the record scratches.
```bash
go install github.com/thebanri/limoni/apps/pikap@latest
pikap # follow what is playing
pikap ~/Music # or play files
```
### Used by
- [**residual**](https://git.merith.xyz/residual/) — a work-in-progress Alpine-based OS with a
from-scratch Go userspace.
---
## Two ways to write an app
| | Immediate mode | Declarative (Elm architecture) |
| :--- | :--- | :--- |
| **Entry point** | `limoni.Run(func(f, ev) bool)` | `limoni.RunProgram(ctx, model)` |
| **State lives in** | your closure | a `limoni.Model` with `Init` / `Update` / `View` |
| **Best for** | dashboards, 3D, games, animation | forms, wizards, CRUD tools, async work |
| **Runtime gives you** | a redraw on every event | commands, cancellation, panic recovery, session recording |
Both use the same renderer and widgets and are available from the root package.
[`examples/counter`](examples/counter) is a complete declarative app in under 80 lines.
Coming from Bubble Tea? See the [migration guide](docs/bubbletea-migration.md).
---
## Widgets
| Category | Widgets |
| :--- | :--- |
| **Layout** | `VStack` / `HStack` / `ZStack`, `Flex`, `Border`, grid layout (`layout.GridLayout`), `Block` (with border merging), `SplitPane` (draggable), `Viewport`, `Dialog`, `Popup`, `StatusBar` |
| **Data** | `Table` (virtual), `List` (virtual), `TreeView`, `FilePicker`, `Calendar`, `Sparkline`, `ProgressBar`, `Gauge`, `LineGauge`, `RichText` |
| **Charts** | `LineChart`, `BarChart`, `PieChart` — Braille, sextant or quadrant markers |
| **Input** | `TextInput`, `Autocomplete`, `TextArea`, `Checkbox`, `RadioGroup`, `Select`, `Slider`, `ColorPicker` |
| **Navigation** | `Tabs`, `Scrollbar`, `CommandPalette`, fuzzy search, keybinding manager |
| **Feedback** | `Spinner`, `Toast`, desktop notifications (OSC 9 / OSC 99) |
| **Graphics** | `Canvas` (Braille, sextant, quadrant, block), 3D meshes as dots or as a picture over kitty/iTerm2/Sixel, `Image` |
| **Text** | `Markdown`, `CodeView` (syntax highlighting), `BigText`, `Label`, `Paragraph` |
| **Tooling** | `DevTools` HUD (`F12`), themes, validation |
→ [Widget gallery](docs/widget-gallery.md) · [Widget reference](docs/widgets-reference.md)
---
## Examples
| Example | What it shows |
| :--- | :--- |
| [`demo`](examples/demo) | The feature trailer: a 3D lemon in ASCII, Braille and half-blocks |
| [`xray`](examples/xray) | A night city under an X-ray: every cell the diff sends lights up, with measured bytes against a full repaint (`-film` for recording) |
| [`showcase`](examples/showcase) | Tabs, forms, matrix rain, 3D, command palette, DevTools (`F12`) |
| [`3d_viewer`](examples/3d_viewer) | OBJ/STL/PLY viewer with shading and orbit controls (`-fps 240`) |
| [`dashboard`](examples/dashboard) | Live CPU and memory sparklines, a process table, streaming logs |
| [`table_virtual`](examples/table_virtual) | A one-million-row table |
| [`agent_checklist`](examples/agent_checklist) | An app built to be driven by an AI agent, and tested with `uitest` |
| [`todo`](examples/todo) | A declarative todo app with tags, filters and fuzzy search |
| [`counter`](examples/counter) | The smallest declarative app |
| [`composable`](examples/composable) | Layout with `VStack`, `HStack`, `Border`, `Flex` |
| [`forms`](examples/forms) · [`layer_demo`](examples/layer_demo) · [`treeview`](examples/treeview) · [`charts`](examples/charts) | Inputs, modals, file tree, charts |
| [`ssh_server`](examples/ssh_server) · [`wasm`](examples/wasm) | Serving over SSH, running in the browser |
Run any of them with `go run ./examples/`, or without cloning:
`go run github.com/thebanri/limoni/examples/3d_viewer@latest`.
All examples: [docs/examples.md](docs/examples.md).
---
## Documentation
| | |
| :--- | :--- |
| [Getting started](docs/getting-started.md) | Install, first app, both application models |
| [Architecture](docs/architecture.md) | The flat cell grid, the diff, why the draw path doesn't allocate |
| [Layout](docs/layout-guide.md) · [Widgets](docs/widgets-reference.md) · [Core API](docs/core-api.md) | Reference |
| [Semantic automation](docs/automation.md) | The automation socket, `limoni-mcp`, `uitest` and the security model |
| [Session recording](docs/session-recording.md) | Record and replay sessions as regression tests |
| [Graphics](docs/graphics-and-canvas.md) · [Animation](docs/animation-and-physics.md) · [Accessibility](docs/accessibility-and-theming.md) | Feature guides |
| [Drivers and platforms](docs/drivers-and-platforms.md) | Unix, Windows, WebAssembly, SSH |
| [How it compares](docs/comparison.md) | Against Bubble Tea v1/v2, Lip Gloss and Ratatui, with the caveats |
| [Benchmarks](docs/benchmarks.md) | Every measured number and how to reproduce it |
| [Rendering FAQ](docs/faq.md) | Hairline gaps, recommended terminals, emoji |
| [Stability](docs/stability.md) · [Changelog](CHANGELOG.md) | What may change before 1.0 |
Turkish documentation: [docs/tr](docs/tr/README.md).
---
## Status
Limoni is **pre-1.0**. Patch releases don't break the API; minor releases may, and
every break is listed in the [changelog](CHANGELOG.md). The core renderer, layout and
widgets are settling; the automation, `uitest` and session packages are new and
experimental. See [docs/stability.md](docs/stability.md) for what has to happen
before v1.0.
## Community and contributing
- **Questions and ideas:** [GitHub Discussions](https://github.com/thebanri/limoni/discussions)
- **Bugs:** [open an issue](https://github.com/thebanri/limoni/issues/new/choose). The template asks for your terminal emulator, since most rendering bugs depend on it.
- **First contribution:** issues labelled [`good first issue`](https://github.com/thebanri/limoni/labels/good%20first%20issue) are scoped to one file and say how to verify the change. Start with [CONTRIBUTING.md](CONTRIBUTING.md).
- **Built something?** Add it to [AWESOME.md](AWESOME.md).
- **Like it?** A ⭐ helps others find it, and you can [buy me a coffee](https://buymeacoffee.com/thebanri).
AI assistants (Claude, Gemini) were used during development for scaffolding, tests
and documentation drafts. The architecture was designed, profiled and benchmarked
by the author, and the benchmark harness exists to check claims, from people or tools.
[Security policy](SECURITY.md) · [Code of Conduct](CODE_OF_CONDUCT.md) · Apache License 2.0