Design UX

design-ux — usability audit (heuristic evaluation)

When to Use

Use this skill when you need uX / usability audit — heuristic evaluation of INTERACTIVE UIs (not just visual polish). Load with design when a UI "feels off", "sucks to use", is hard to learn, needs an instruction wall, or before shipping an interactive tool/editor/app. Scores the RENDERED UI against Nielsen's 10 +...

Usability ≠ aesthetics. design-system/design-spatial make it look right; this checks whether a first-timer can do the task without being told how. Use it whenever a UI "sucks to use," needs a paragraph of instructions, or before shipping anything interactive.

Rule 0 — fresh eyes, on the rendered artifact (inherited from design-spatial §1)

Never self-grade. The builder rationalizes its own UI. Render the live UI in its default first-load state (not a hand-arranged screenshot), capture an interaction trace of the primary task, and have a separate judge (a subagent/VLM that did NOT build it) score it. A described list of changes is not an audit — the audit is a fresh judge hunting for what's wrong on the real screen.

The procedure

1. Name the primary task(s) the UI exists for (e.g. "trim a clip and set its speed, then export"). The audit is relative to these, not to abstract prettiness.
2. Render default state + trace the task. Screenshot the first-load UI (wide AND narrow — overflow gate from design-spatial §2). Then actually perform the primary task and screenshot each step.
3. Score every heuristic (table below) on the artifact: pass / violation, severity (blocker / major / minor), a specifically located finding, and a concrete fix. Separate judge does this.
4. Prioritize: blockers → majors → minors; cluster fixes that touch the same surface.
5. Fix, then RE-RENDER and RE-SCORE. Do not claim fixed without re-auditing the new artifact (verify-outputs-rule).

Heuristics — score each (Nielsen's 10, 1994) + interaction add-ons

Interaction add-ons (compose, don't restate):

• Don't-make-me-think (Krug): affordances self-evident; the UI teaches itself. Instruction paragraph ⇒ affordance debt (ties to #6).
• Fitts / transit time (design-spatial §3): controls sit near where the task leaves the cursor. A selected object's properties belong adjacent to the object (dock/popover), not in a far panel — every edit shouldn't be a round-trip.
• Discoverability of gestures: any non-obvious gesture (wheel, edge-drag, dbl-click) needs a visible affordance (handle, hover cue, icon) or it doesn't exist for most users.
• Visual-weight match (design-spatial): the surface the user operates (timeline, canvas, editor) should be the visual hero — not a thin strip under a big passive preview.
• Progressive disclosure (design-thinking UX): essentials first; advanced on demand. But disclosure ≠ hiding the primary tool.
• Tooltip timing: delay the first tooltip in a group (~300–700ms hover-intent) so sweeping the cursor over controls doesn't flash tips; once one is open, peers show instantly (no per-tooltip re-delay) while the user scans the row. Fires-on-every-hover is noise; re-delays-on-each-neighbor is sluggish.
• Scroll-position restore: Back/Forward returns the user to where they were, not the top — losing place after a detail→back trip is a silent, repeated tax. Browsers do this by default; the bug is breaking it with manual scroll resets or client routing that forgets.
• Idempotency on submit: mutating actions carry an idempotency key so a double-click, retry, or flaky-network resend can't duplicate the effect (a second charge, a duplicate post). Pairs with "disable submit during the in-flight request + spinner" — the key is the server-side guarantee, the disable is the client-side courtesy.

(Tooltip / scroll-restore / idempotency from the Web Interface Guidelines, vercel-labs/web-interface-guidelines @ 4e799d4, 2026-04-06.)

Output format

A scored table — Heuristic | Finding (located) | Severity | Fix — then a prioritized fix list (blockers first). Severity: blocker = can't complete the task / actively misleading; major = slows or confuses; minor = polish.

Relation to the rest of design

• design-spatial owns the render-then-critique mechanism + Fitts/transit + overflow gate; this skill applies that lens to usability specifically and adds the heuristic scorecard.
• design-thinking owns the UX principles (goals/tasks, IA, feedback, accessibility, progressive disclosure); this skill turns them into a scored audit + fix loop.
• Run a usability audit before declaring an interactive UI "done" — alongside the visual critique, not instead of it.

Limitations

• Use this skill only when the task clearly matches its upstream source and local project context.
• Verify commands, generated code, dependencies, credentials, and external service behavior before applying changes.
• Do not treat examples as a substitute for environment-specific tests, security review, or user approval for destructive or costly actions.