Wails

Wails: Desktop Apps in Go

Wails builds native desktop applications with a Go backend and a web frontend rendered in the platform webview (WebKit on macOS/Linux, WebView2 on Windows). No bundled Chromium — binaries are megabytes, not hundreds of megabytes.

Two major versions coexist, with incompatible APIs. v2 is stable. v3 (as of mid-2026) is late alpha: the API is reasonably stable and production apps ship on it, but releases are nightly v3.0.0-alpha2.x tags and details still move. The single most common failure mode — for LLMs especially — is mixing v2 and v3 code. Every response must be pure v2 or pure v3.

Step 0 — Detect the Version (Mandatory)

Before writing any code, determine the version from the project. Do not guess from the user's phrasing.

New project with no code yet: default to v2 if the user needs stability and zero churn; recommend v3 for a new long-lived app if they accept alpha status — the architecture is better (multi-window, services, transparent builds) and it's the future. State the trade-off in one sentence and pin the exact alpha version in go.mod. Never present v3 as stable.

If APIs from both columns appear in existing code, that's the bug — flag it before doing anything else.

Wails v2 (Stable)

Canonical main.go

//go:embed all:frontend/dist
var assets embed.FS

func main() {
    app := NewApp()

    err := wails.Run(&options.App{
        Title:  "myapp",
        Width:  1024,
        Height: 768,
        AssetServer: &assetserver.Options{Assets: assets},
        OnStartup:  app.startup,
        Bind: []interface{}{app},
    })
    if err != nil {
        log.Fatal(err)
    }
}

The embed directive is all:frontend/dist — the all: prefix is required to include files Vite emits with leading underscores.

The Context Capture Pattern

Everything in the v2 runtime requires the context handed to OnStartup. Store it; this is the load-bearing idiom of every v2 app:

type App struct {
    ctx context.Context
}

func (a *App) startup(ctx context.Context) {
    a.ctx = ctx // required for all runtime calls
}

func (a *App) OpenFile() (string, error) {
    return runtime.OpenFileDialog(a.ctx, runtime.OpenDialogOptions{})
}

• Never call runtime.* before OnStartup fires — the context doesn't exist yet. This is the classic v2 startup crash.
• runtime here is github.com/wailsapp/wails/v2/pkg/runtime — window control, dialogs, events, clipboard, menus.

Bindings and Events

• Exported methods on bound structs become async JS functions under wailsjs/go/main/App. A Go (value, error) return becomes a resolved/rejected Promise.
• Go→JS: runtime.EventsEmit(a.ctx, "name", data); JS side EventsOn("name", cb) from wailsjs/runtime.
• Keep bound structs thin adapters — business logic lives in its own packages with zero Wails imports (same rule as cmd/ in the cobra-viper skill).

v2 Common Mistakes

• Calling runtime functions before startup (nil/invalid context).
• Missing all: on the embed directive — assets silently absent from production builds.
• Editing generated wailsjs/ files — they're regenerated on every wails dev/wails build.
• Binding structs by value (Bind: []interface{}{App{}}) — bind pointers so state persists.

Wails v3 (Alpha)

Canonical main.go

//go:embed all:frontend/dist
var assets embed.FS

func main() {
    app := application.New(application.Options{
        Name: "myapp",
        Assets: application.AssetOptions{
            Handler: application.AssetFileServerFS(assets),
        },
        Services: []application.Service{
            application.NewService(NewGreetService()),
        },
    })

    app.Window.NewWithOptions(application.WebviewWindowOptions{
        Title: "myapp",
    })

    if err := app.Run(); err != nil { // blocks; must run on the main goroutine
        log.Fatal(err)
    }
}

Use the Manager API style — app.Window.NewWithOptions, app.Event.On, app.Menu.New(), app.SystemTray.New(). Earlier alphas used flat methods (app.NewWebviewWindowWithOptions, app.OnEvent); tutorials and LLM training data are full of them. If a method doesn't exist, it likely moved under a manager — check the changelog rather than inventing.

Services: the v3 Binding Model

Services replace v2's Bind. A service is a plain struct; exported methods are bound, and two optional lifecycle methods hook the app:

type NoteService struct {
    db *sql.DB
    mu sync.RWMutex
}

func (s *NoteService) ServiceStartup(ctx context.Context, opts application.ServiceOptions) error {
    // open resources, run migrations, start background goroutines governed by ctx
    return nil // returning error aborts app startup
}

func (s *NoteService) ServiceShutdown() error {
    return s.db.Close() // services shut down in reverse registration order
}

func (s *NoteService) Save(n Note) error { ... } // callable from JS

• Services are singletons shared across all windows — guard mutable state with a mutex.
• Dependencies go in via plain constructors (application.NewService(NewNoteService(db, logger))) — no DI framework.
• A service can serve HTTP by implementing http.Handler and registering with application.NewServiceWithOptions(svc, application.ServiceOptions{Route: "/files"}).
• Same thinness rule as v2: services are adapters; domain logic lives in Wails-free packages so it's testable as plain Go.

Bindings, Events, Windows

• Generate frontend bindings with wails3 generate bindings (run automatically by wails3 dev). Import from frontend/bindings/<full-go-import-path>/<service> — not wailsjs/.
• Events: app.Event.Emit("name", data) / app.Event.On("name", handler); OS-level via app.Event.OnApplicationEvent(events.Common.ApplicationStarted, ...). Cancellable hooks: window.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) { e.Cancel() }) — the standard "confirm before close" pattern.
• Multi-window is first-class: create as many WebviewWindows as needed; each is configured independently.

Build System

v3 builds are orchestrated by go-task via Taskfile.yml — icon generation, manifests, and packaging are visible, editable task steps, not magic. Customize by editing tasks, not by fighting the CLI. Platform packaging: wails3 package (.app/dmg on macOS, NSIS on Windows, AppImage/deb on Linux).

Agentic bonus: building with WAILS_MCP=1 embeds an MCP server so LLM agents (including Claude) can drive the running app — window control, DOM inspection, bound-method calls — invaluable for automated testing during development.

v3 Alpha Discipline

• Pin the alpha version in go.mod and upgrade deliberately, reading the changelog (v3.wails.io/changelog) — nightly alphas can rename APIs.
• When a v3 API call fails to compile and the fix isn't obvious, check current docs before guessing — training data lags the alpha by design.

Version-Mixing Tells (Reject on Sight)

• runtime.EventsEmit(ctx, ...) or pkg/runtime imports in a v3 project → v2 API; use app.Event.Emit.
• application.New(...) or pkg/application in a v2 project → v3 API; use wails.Run(&options.App{...}).
• Frontend importing wailsjs/go/... in v3 (should be frontend/bindings/...) or vice versa.
• Running wails dev against a v3 project or wails3 dev against v2.
• Bind: field inside application.Options, or Services: inside options.App — each belongs only to its own version.

Shared Principles (Both Versions)

• The frontend is untrusted input: validate arguments in bound methods exactly as you would HTTP handlers; never build shell commands or file paths from raw frontend strings.
• Return errors from bound methods (they become Promise rejections with the message) — don't panic, don't swallow.
• Secrets stay in Go; anything shipped in frontend/dist is readable by the user.
• Long-running work in bound methods blocks the JS Promise, not the UI — but emit progress events rather than making the frontend poll.