Limoni

🍋 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.

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Quick start

go get github.com/thebanri/limoni

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:

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 · Widget gallery · Examples

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Why Limoni

1. Your TUI has a semantic tree, so tests and agents address widgets by name

Most terminal automation, such as termwright or 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.

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.

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

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.
• 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.

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 and the methodology. One earlier run showed a 4,700× lead; it came from a bug in the benchmark harness, and the methodology explains how it was caught.

3. Batteries that other TUI libraries leave to you

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).
• 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), 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.

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Built with Limoni: zest

**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.

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: the "Logs · zest" scene.

And: globe

**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.

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** 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.

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. The same scenes go behind any Limoni application with limoni.WithBackdrop(backdrop.Aurora()).

And some games

**Lemon Drop** 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.

go install github.com/thebanri/limoni/apps/lemondrop@latest
lemondrop

Or play it in the browser, with sound and a world leaderboard.

**Lemon Snake** 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.

go install github.com/thebanri/limoni/apps/lemonsnake@latest
lemonsnake

Or play it in the browser, with its sound and the world leaderboard.

**Lemon Sweep** 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.

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, where the pointer is locked for mouse look. A frame allocates nothing, the most broken build's full pools included.

**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.

go install github.com/thebanri/limoni/apps/pikap@latest
pikap            # follow what is playing
pikap ~/Music    # or play files

Used by

• **residual** — a work-in-progress Alpine-based OS with a from-scratch Go userspace.

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Two ways to write an app

Both use the same renderer and widgets and are available from the root package. examples/counter is a complete declarative app in under 80 lines. Coming from Bubble Tea? See the migration guide.

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Widgets

→ Widget gallery · Widget reference

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Examples

Run any of them with go run ./examples/<name>, or without cloning: go run github.com/thebanri/limoni/examples/3d_viewer@latest. All examples: docs/examples.md.

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Documentation

Turkish documentation: docs/tr.

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Status

Limoni is pre-1.0. Patch releases don't break the API; minor releases may, and every break is listed in the changelog. The core renderer, layout and widgets are settling; the automation, uitest and session packages are new and experimental. See docs/stability.md for what has to happen before v1.0.

Community and contributing

• Questions and ideas: GitHub Discussions
• Bugs: open an issue. The template asks for your terminal emulator, since most rendering bugs depend on it.
• First contribution: issues labelled good first issue are scoped to one file and say how to verify the change. Start with CONTRIBUTING.md.
• Built something? Add it to AWESOME.md.

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 · Code of Conduct · Apache License 2.0