Build GPUI Apps

Build native GPUI software that is correct before it is glossy, genuinely platform-aware before it is Apple-styled, and verified in the running app before it is called complete.

This is a routed umbrella skill. Read only the reference layers needed for the task, but always follow the core contract and workflow below.

Core contract

1. Inspect the target checkout before changing it: branch, dirty state,

manifests, lockfile, pinned GPUI source, app entrypoint, root view, theme, components, assets, tests, and platform code.

1. Treat the target checkout as the API authority. GPUI is pre-1.0; examples

from gpui.rs, Zed main, crates.io, or this skill can differ from the pinned revision.

1. Preserve working state ownership, commands, shortcuts, persistence, window

behavior, and platform integration. A visual request is not permission to replace the app architecture.

1. Keep render work deterministic and cheap. Move blocking I/O and CPU-heavy

work off the application thread, then update a live entity through the appropriate async context.

1. Give interactive elements stable IDs, semantic roles, keyboard access,

visible focus, disabled behavior, and immediate input feedback.

1. Use glass as a functional navigation or control layer, not as decoration on

every surface. Never describe a flat translucent rectangle as native Liquid Glass.

1. Respect reduced motion, reduced transparency, increased contrast, and

differentiate-without-color. Provide an opaque fallback.

1. Validate compilation, behavior, launch, and visuals. cargo check alone

does not prove focus, fonts, window chrome, scale factor, clipping, motion, or material behavior.

1. Do not rasterize text, controls, panels, or whole screens to fake fidelity.
2. Preserve unrelated changes and report every unverified platform or runtime

path plainly.

1. Treat text input, clipboard, menus, drag/drop, and window lifecycle as OS

contracts. Preserve Unicode range units, composition, focus, command state, and stable ownership.

1. For a new application, establish product identity, a pinned toolchain and

GPUI revision, observable startup, storage policy, CI, and packaging gates before calling the starter production-ready.

Route the task

Workflow

1. Establish scope and current truth

Run the read-only inspector:

scripts/inspect_gpui_project.sh /path/to/project

Then inspect directly:

• Read repository instructions and determine whether the request authorizes

edits or only diagnosis/review.

• Confirm the owning crate and the smallest surface that can satisfy the task.
• Record the GPUI declaration and exact lockfile version or Git revision.
• Find a similar component that compiles in this checkout.
• Identify current theme access, asset loading, focus conventions, actions,

overlay system, async patterns, and test support.

• Note the platform and minimum OS versions. Do not silently make a

cross-platform component macOS-only.

Read [project-versioning.md](references/project-versioning.md) before creating a new app, changing startup, changing GPUI versions, or copying an upstream API.

For a greenfield or starter-hardening request, read [production-starter.md](references/production-starter.md) before choosing the crate layout. It uses lassejlv/gpui-starter as a concrete minimal example, then adds the missing production contracts without pretending every app needs every subsystem.

2. Write the behavioral contract

Before implementation, state:

• source of truth for state;
• user actions and resulting events/state transitions;
• loading, empty, disabled, error, and cancellation states;
• focus owner, tab order, shortcuts, pointer and touch behavior;
• text index units, composition, clipboard, menu, and window ownership when in

scope;

• resize and scrolling behavior;
• material tier and fallbacks;
• reduced-motion, opaque, and high-contrast behavior;
• target platforms and what must be verified on each.

For a visual translation, add the exact source frame, viewport, theme, fonts, assets, and screenshot evidence.

3. Choose the smallest correct GPUI register

Use:

• an ordinary element tree for normal layout and styling;
• RenderOnce for stateless, value-like reusable components;
• an Entity<T> implementing Render for independently changing state;
• a project model entity for shared domain state;
• canvas or a custom Element only when ordinary layout or painting cannot

meet the requirement;

• a narrow platform bridge only for behavior GPUI cannot supply.

Do not create an entity for every wrapper. Do not keep meaningful state in ephemeral render-local values. Read [architecture-state.md](references/architecture-state.md) and [components-layout.md](references/components-layout.md).

4. Implement one vertical slice

Build one end-to-end path before broad extraction:

1. Domain state or model operation
2. Typed action or event
3. Entity update
4. cx.notify() or emitted event
5. Rendered default state
6. Pointer, keyboard, focus, and accessibility behavior
7. Error/cancellation state
8. Targeted test

Only extract a reusable component or token after a repeated semantic or visual pattern is proven. Keep public APIs narrow and predictable.

5. Apply Apple design without lying about capability

Select the material tier in this order:

1. Existing system or project component
2. Native macOS 26+ NSGlassEffectView behind an availability boundary
3. NSVisualEffectView or GPUI whole-window blur when that is the actual need
4. Cross-platform GPUI approximation using semantic tint, border, highlight,

shadow, and opacity

1. Opaque/high-contrast fallback

Do not stack glass on glass. Keep content surfaces mostly solid. Use concentric geometry, restrained tint, adaptive light/dark tokens, and clear elevation. Read [apple-glass.md](references/apple-glass.md).

6. Make interaction physical and interruptible

• Respond on press/down, then commit on release/click.
• Keep direct manipulation 1:1 and preserve the grab offset.
• Carry velocity from gesture to settling motion.
• Retarget from current presentation state and velocity.
• Keep input active while motion runs.
• Use symmetric enter/exit paths and anchor presentations to their source.
• Prefer AnimationExt::with_animation for decorative finite motion when the

pinned version supports it; it integrates with GPUI reduced-motion state.

• Use explicit state plus frame requests for interactive springs. The bundled

[spring.rs](assets/spring.rs) is a pure-Rust starting point, not a substitute for target-version integration.

Read [motion-input.md](references/motion-input.md) before implementing custom animation or gestures.

For editable text, native command surfaces, drag/drop, or more than one window, read [input-windows.md](references/input-windows.md). Prefer a maintained editor component over implementing the platform input contract from scratch.

7. Protect lifecycle and performance

• Hold a returned Task when dropping it should cancel work; detach only when

app-lifetime completion is deliberate and errors are observed.

• Hold a Subscription when the observer has an owner; detach only when entity

lifetime semantics are correct.

• Capture WeakEntity in long-running work.
• Use background_spawn for blocking/CPU work and cx.spawn or

cx.spawn_in for application-thread orchestration.

• Virtualize large collections with list or uniform_list.
• Avoid filesystem, network, sleep, parsing, and unbounded allocation in

render.

• Request animation frames only while something is changing.

Read [async-performance.md](references/async-performance.md).

8. Validate in widening rings

Run repository-native checks first, then adapt this baseline:

cargo fmt --check
cargo check -p <owning-crate>
cargo test -p <owning-crate>
cargo clippy -p <owning-crate> --all-targets -- -D warnings

Also:

• launch the real app;
• exercise mouse, keyboard, focus, resize, scroll, and relevant touch paths;
• verify light, dark, inactive-window, reduced-motion, opaque, and

high-contrast states where supported;

• capture matching screenshots for visual work;
• check at 1x and a high-DPI scale;
• inspect logs and task/error states;
• run at least one targeted #[gpui::test] when behavior uses GPUI input,

focus, actions, timing, or windows.

Read [testing-qa.md](references/testing-qa.md) and [visual-validation.md](references/visual-validation.md).

This skill includes a compile-checked, exact-revision fixture at assets/reference-app. It demonstrates startup, actions, entity events, owned async work, accessibility, menus, multiple windows, virtualization, preference-aware material fallbacks, and spring orchestration. It is a pattern fixture, not a production component framework. Validate it with:

scripts/validate_reference_app.sh

Production starter path

For “create a GPUI app,” “set up a starter,” or “make this starter production-ready”:

1. Gather the product name, package/binary slug, owned application ID,

supported platforms, minimum OS versions, distribution route, durable data, and update owner.

1. Inspect the target and the exact starter/example commit. Never copy over an

existing checkout or delete its Git history without authorization.

1. Keep the minimal desktop/ui split until domain code proves a separate

headless crate.

1. Pin the Rust toolchain and GPUI Git revision, commit Cargo.lock, and make

the first clean CI baseline reproducible.

1. Rename identity across crates, binary, action namespace, app ID, menus,

storage, icons, packaging, and update metadata.

1. Add observable startup, configuration/migrations, secret storage,

lifecycle-owned async work, accessible controls, diagnostics, and recovery only where the product requires them.

1. Replace the demo with one real vertical slice and test it from domain state

through action, GPUI update, persistence/error state, restart, and release launch.

1. Build, sign, install, upgrade, and exercise real artifacts on every claimed

platform. Report cross-compilation separately.

Do not call a raw release binary, a green cargo check, or the unmodified minimal example production-ready. Use the complete acceptance matrix in [production-starter.md](references/production-starter.md).

Paper.design path

Use this path when Paper is one input to broader GPUI app, architecture, or production work. When faithful translation of a selected Paper frame is the primary task, route to the standalone paper-to-gpui skill instead.

For Paper input within broader work:

1. Require a live Paper MCP connection and one exact selected frame or node ID.
2. Verify the open file with getbasicinfo and intent with get_selection.
3. Capture a 2x screenshot, hierarchy, JSX as structural evidence, computed

styles, fonts, tokens, and actual exportable assets.

1. Preserve the GPUI app architecture and translate layout semantics, not DOM

wrapper count.

1. Implement geometry, typography, paint, assets, and interactions in that

order.

1. Compare Paper and native screenshots at matching logical bounds.

If Paper is unavailable, stop the design extraction path and explain how to connect it. Do not recreate the design from memory. Read [paper-to-gpui.md](references/paper-to-gpui.md) and [paper-mcp.md](references/paper-mcp.md).

Review standard

Rank findings by user impact and confidence. Require evidence for claims about:

• stale or dropped tasks/subscriptions;
• missed cx.notify() calls;
• unstable or duplicate element IDs;
• focus traps or pointer-only controls;
• blocking application-thread work;
• unbounded render allocation;
• incorrect fixed sizing or clipping;
• unsupported blur/material claims;
• missing accessibility role, label, state, or action;
• animation that ignores reduced motion;
• platform API use without availability guards;
• green compilation presented as visual or runtime proof.

Do not turn style preferences into correctness findings.

Completion report

Report:

• GPUI version/revision and target platforms;
• files and architectural boundaries changed;
• material tier and fallback behavior;
• interaction, focus, accessibility, async, and performance behavior;
• text/IME, command, window lifecycle, and restoration behavior when relevant;
• tests, builds, launch, and visual comparisons actually performed;
• remaining deltas, unverified platforms, and version-sensitive assumptions.

For the research snapshot behind this skill, read [sources.md](references/sources.md). Refresh upstream APIs when the target revision differs or the snapshot is no longer current.

After substantial suite changes, run the realistic prompts and reviewer-only rubrics in [forward-tests.md](tests/forward-tests.md) with fresh agents. Fix routing or instruction gaps before publishing.