Imported from gilbarbara/color-lab (.claude/skills/validate-ui/SKILL.md). Install upstream with npx skills add gilbarbara/color-lab --skill validate-ui. Copyright stays with the author.

Validate the Color Lab UI

Drive the real app as a user and prove a feature works. Assert between actions — never chain two on an assumption; the loop below is why.

Read this file, then read exactly one references/<area>.md for the area you're validating. Don't load them all.

The loop

1. act      — one command
2. observe  — snapshot (or get the specific observable)
3. assert   — the thing you expected to change actually changed
4. repeat

You cannot see the page. You are working from a mental model, and the model is wrong the moment you act. So you re-read after every action — not when something looks broken, because it will not look broken.

`✓ Done` is not a result

agent-browser prints ✓ Done when the command ran. It says nothing about whether it did anything. Every trap in this file is an instance of that:

Command	Prints	Actually
`fill` on a slider	`✓ Done`	value jumped to the range's midpoint
`type` / `keyboard type` / `select` on a slider	`✓ Done`	nothing at all
`focus` on a control in a collapsed panel	`✓ Done`	focus went nowhere (`inert`) — every later `press` is swallowed
clicking a `[disabled]` button	`✓ Done`	nothing at all — and the unchanged state reads as a real result
`find role button click --name "Save"`	`✓ Done`	hit `Save palette`, not the modal's `Save`
clicking a toggle whose state was persisted open	`✓ Done`	you just closed it

None of these error. All of them produce a green, confident, wrong result. The only defence is to look.

So: never chain two actions on an assumption. After a click that opens something, assert it opened. After a click that toggles something, assert which way it went. Re-snapshot before reusing any @ref — refs die on every re-render.

A covered control is not one of these traps: any click on one errors and names the covering element (✗ covered by <header.fixed.top-0>). That's a signal, not a failure — read it and clear the coverer.

Prefer click @ref over find role … click anyway: find matches by substring, so a name that looks unique often isn't — --name "Save" hits Save palette, and a bare Select matches Select <Name>, Select variant and Select lock at once. A @ref names exactly one.

What the app is

An OKLCH color-scale generator. You pick base colors; it generates a tonal scale (3–20 steps) for each. Everything else — curves, groups, presets, export, contrast tools — feeds or renders that.

The palette IS the URL. Every structural edit rewrites the address bar; back/forward is undo/redo. This is why most assertions are URL assertions: if the URL didn't change, the edit didn't happen.

Routes: / redirects to /p. /p/<slug> is the entire generator. /palettes is the saved list (auth-gated). /about, /privacy, /terms, /oklch-vs-hsl, /custom-color-scales are static.

Boot

The dev server is https://color-lab.localhost (portless proxy) — not localhost:3000.

pnpm dev   # if it isn't already up

agent-browser open https://color-lab.localhost/p/Primary-73.0_0.23001_321
agent-browser set viewport 1440 900
agent-browser wait --load networkidle

Two seed palettes, from e2e/__setup__/constants.ts:

single — /p/Primary-73.0_0.23001_321
palette — /p/Primary-60_0.21_150/Secondary-60_0.139_227/Tertiary-60_0.266_304

Each area file names the seed it wants.

The single seed rewrites itself on load. That is expected. Plain precision rounding, in P3 and sRGB alike — formatOklchUrl (src/utils/color.ts) rounds L to 2 decimals and C to 3:

/p/Primary-73.0_0.23001_321   →   /p/Primary-73_0.23_321
        ^^^^ trailing zero          ^^^^^^^ 0.23001 → 0.23

Assert against Primary-73_0.23_321. The palette seed is canonical and stays put. Gamut has nothing to do with it — e2e/basic.spec.ts:56 asserts the rewritten form while forcing P3.

Step zero: read the opening state, don't assume it

appStore persists to localStorage (key color-lab). A pre-paint script in app/layout.tsx stamps some of it onto <html> before React mounts. The starting state is restorable, not fixed.

Persisted: gamut, showSidebar, showPreview, showColorOptionsPanel, showPaletteOptionsPanel, view, colorSpacing, exportFormatType, exportColorFormat.

view, colorSpacing and the two export settings are persisted but are not on <html>. A reload restores whatever you last left — not List view, not Wide spacing, not the default export tabs.

A toggle you click may already be on, so your click turns it off. Read the state first; if it isn't what the area file expects, set it explicitly or clear storage.

The three observables

Don't eyeball screenshots. Screenshots are for showing the human.

1. The URL — the palette state. Colors are path segments (/p/Name-L_C_H); options are short query keys. Per-color overrides ride on the segment after a -, comma-separated (Primary-60_0.21_150-f:1.2,k:400).

Key	Means	Key	Means
`i`	steps (3–20)	`s` / `o`	saturation / apply-to-all
`m`	mode `l`/`d`/`r`	`k`	locked step
`v`	variant	`f`	lightness curve
`c`	chroma curve	`h`	hue shift
`n` / `x`	min / max lightness	`g`	group: `b`/`n`/`s`/`d`

Defaults are dropped from the URL entirely — so "reset" is asserted as the param disappearing, not as it returning to a value.

2. <html> — the app's chrome state. Global layout flags with no accessible surface, so there is nothing in the tree to read instead:

agent-browser eval "JSON.stringify(document.documentElement.dataset)"
# {"gamut":"srgb","p3Supported":"false","sidebar":"open","preview":"open",
#  "colorOptions":"closed","paletteOptions":"closed"}

data-gamut (p3|srgb) · data-sidebar · data-preview · data-color-options · data-palette-options (each open|closed) · data-p3-supported. dataset camelCases them — dataset.colorOptions, not dataset['data-color-options']. Dark mode is class="dark", not a data attribute.

Three different surfaces say "color options" — keep them apart. data-color-options tracks only the global Advanced Options panel (showColorOptionsPanel). The per-color Change color options Collapse has no chrome flag — it's proven open by its inputs being mounted. Steps/variant/lock live under data-palette-options.

Headless Chrome reports p3Supported: "false", so the app opens in gamut: srgb — the environment, not a bug. It does mean you validate the sRGB path by default, which the e2e suite never exercises (it forces P3 on).

3. ARIA — element state. aria-current on the active ColorItem · aria-pressed on group chips · aria-selected on tabs · aria-checked on radios · aria-expanded on Toggle Bottom Bar.

agent-browser snapshot -i              # your default read
agent-browser get count '[data-testid=Scale]'
agent-browser get attr @e5 aria-pressed
agent-browser get url

The `eval` rule

Read state through the accessibility tree, not the DOM. eval has exactly three legitimate uses:

Reading <html>'s data-* chrome state (observable 2 — it has no ARIA surface by design).
Patching navigator.clipboard (clipboard reads are blocked).
setRange — setting a channel slider's value, because agent-browser genuinely cannot (see Sliders).

Everything else — element counts, aria-*, text, tab selection, panel contents — comes from snapshot / get.

Reaching for eval to prove a control's state — className, getComputedStyle, getBoundingClientRect, a bare data-* — means stop. That control has no accessible state, and that is an accessibility bug. Report it. Class-sniffing hides the defect and trains the next agent to hide it too.

The distinction that matters: eval is banned as a substitute for looking. It is correct as an implementation of an action agent-browser can't perform. setRange is the second; it is not a licence for the first.

eval reuses one JS context, so a bare const x = … throws Identifier 'x' has already been declared on the second call. Wrap every body in an IIFE.

Sliders

Every slider is an <input type="range">, but they come from two libraries that commit on different events. That, and only that, is why they differ.

Slider	Where	Commits on	Drive with
Channel — `Lightness`, `Chroma`, `Hue`	sidebar `ColorItem`	`input`	`setRange`
Option — steps, saturation, every curve	Palette Options, Advanced Options, per-color overrides	`onChangeEnd`	`focus` + `press`

Both land exactly, in one step. Never fill either.

Option sliders → `focus` + `press`

HeroUI/react-aria. They commit on onChangeEnd, which only real input fires — a synthetic value change does nothing, so setRange will not move the URL here. e2e drives them this way and explains why at e2e/scale.spec.ts:44-48.

agent-browser focus 'input[name="lightnessCurve"]'
agent-browser press PageDown          # 1.3 → 1.2, URL gains ?f=1.2

press takes a key, not a selector — it acts on whatever is focused, so every keyboard step is two commands. Focus persists across presses. One press = one tick: PageUp/PageDown = 0.1 on the curve sliders, 10 on hueShift; arrows = 1 on steps; Home/End = min/max.

Assert the panel is open before you focus. A collapsed panel's content is inert, and an inert input cannot take focus — focus still prints ✓ Done, and every press is silently swallowed. How you assert open depends on the panel: Advanced Options → data-color-options (it flips in lockstep with inert); Palette Options → data-palette-options; a per-color panel → its inputs being present (it unmounts them when closed — see scale.md). Don't read data-color-options for the per-color case; it reports the global panel.

Channel sliders → `setRange`

agent-browser cannot set a range input's value. fill is broken (below); type, keyboard type, keyboard inserttext and select are silent no-ops. Keyboard works but can't reach a target — the step is 0.001 on Lightness/Chroma and 0.01 on Hue (3,600 PageUps to cross 0–360). Don't.

So setRange is the tool. It is not a trick: it is precisely the branch Playwright's fill() takes for range inputs (kInputTypesToSetValue = {color, date, time, datetime-local, month, range, week} → set the value, dispatch input + change, never clear). Same operation e2e/basic.spec.ts performs.

cat <<'EOF' | agent-browser eval --stdin
(() => {
  const el = document.querySelector('input[type=range][aria-label="Hue"]');
  const set = Object.getOwnPropertyDescriptor(HTMLInputElement.prototype, 'value').set;
  set.call(el, '150');
  el.dispatchEvent(new Event('input',  { bubbles: true }));
  el.dispatchEvent(new Event('change', { bubbles: true }));
})()
EOF

The native setter is required: React patches the instance's value setter to track changes, so a plain el.value = … is swallowed and onChange never fires.

Assert on the URL, never on el.value. The picker commits through requestAnimationFrame while React synchronously restores the controlled value, so reading it back in the same eval returns the old value even though the edit landed. Use wait --url "**/*_150".

Channel sliders are 1px × 1px and clipped (the visible track is the parent div). So find role slider --name "Hue" fails to resolve them, even though they do appear as slider in a snapshot. Use @ref or input[type=range][aria-label="Hue"].

Never `fill` a slider

fill is "clear the field, then fill it" — and the clear alone destroys the value. Per the HTML spec, a range input set to '' resets to its default, min + (max-min)/2:

fill Hue            "150"   (min 0,   max 360)   →   180     ← midpoint, not 150
fill lightnessCurve "2.0"   (min 0.1, max 5)     →   2.55    ← midpoint, not 2.0

An agent-browser bug, not app behavior (Playwright fills these fine — hence setRange). Pick a target near the midpoint and you get a green assertion that proves nothing.

URL writes are not debounced

There is no debounce. useUrlSync calls pushState synchronously, so after a discrete edit (Add Color, a menu selection, a name blur) get url already returns the new URL — no wait needed.

The one thing that defers a write is a slider gesture: while any element carries data-interacting="true", useUrlSync pauses and flushes exactly one entry on release (the invariant that stops a drag flooding the back button).

Prefer wait --url "**/<expected>" over a fixed sleep — it costs nothing when the URL is already right. But don't wait on a timeout that doesn't exist: if the URL never arrives, something is genuinely wrong and waiting longer won't fix it.

Selectors

Precedence: role + accessible name → data-testid → input[name=…]. Every selector in the area files is one the e2e suite drives, so a rename breaks CI before it breaks this skill. Prefer them over anything you invent.

Per-color controls carry a for <Name> suffix the area files omit. The real names are View Color Info for Primary, Change color options for Primary, Color group for Primary, Export scale for Primary, Random color for Primary. The area files name the stem, and substring matching makes them work — but an exact-name lookup will fail, and substring matching is also how --name "Save" hits the wrong button. When a stem doesn't resolve, snapshot and read the real name.

Reading the clipboard

navigator.clipboard.readText() throws NotAllowedError here. Two options:

The toast is the assertion — swatch copies and Share raise one ([role=alert]) containing the copied value.
Patch the writer when you need the exact payload (export):

cat <<'EOF' | agent-browser eval --stdin
(() => {
  window.__clip = [];
  const orig = navigator.clipboard.writeText.bind(navigator.clipboard);
  navigator.clipboard.writeText = t => { window.__clip.push(t); return orig(t); };
  return 'patched';
})()
EOF
# …click the copy button, then read window.__clip

App-specific behavior

Facts you cannot derive by looking — the rest is caught by the loop.

A color's editing controls only exist while it's active — sliders, Change color options, Color group, Random color, View Live Preview live in a Collapse gated on isActive. Click Select <Name>, confirm aria-current="true", then look. The name input, color picker, color-value input and Remove button are always rendered — Remove is merely disabled when inactive, so its presence proves nothing.
aria-current is on the ColorItem wrapper, not the Select <Name> button (whose own aria-current is null).
Remove color is click-again-to-confirm, and the one exception to the rule above: send both clicks with no snapshot between them, because a re-render disarms the confirm. The exception buys you nothing if you skip the checks around it — before, the color must be active and the button must not be [disabled] (a disabled Remove takes both clicks, prints ✓ Done twice, and removes nothing); after, assert the segment is gone from the URL.
Delete palette is a Popconfirm — Remove Palette (<name>), then Confirm.
Add Color clicks fired back-to-back get dropped — you land on N-1 colors and it reads as an app bug. It's not the Color Spacing dropdown (it happens with the menu never opened). Click once, assert the ColorItem count went up, then click again.
Panels animate ~400ms. Wait on the data-* attribute flipping, not a sleep.

Overlays

Six components open over the palette. The backdrop decides the behavior: opaque/blur are modal, transparent/none are non-modal — and the two do opposite things to your snapshot.

Component	Backdrop	Modal?	Snapshot while open
`Palette/DisplayMenu`	`opaque`	yes	collapses to the overlay's own content
`ReorderColors`	`opaque`	yes	collapses
`ExportDrawer`	`blur`	yes	collapses
`components/Modal` → Login, Save palette, Contact, Color Info, Contrast Grid	`blur`	yes	collapses (to the modal, which may itself be large)
`ColorList/ColorItem` (color picker)	`transparent`	no	whole page stays in the tree
`Popconfirm`	none	no	whole page stays

Modal (opaque/blur). The app sets aria-hidden on everything behind the overlay, and agent-browser filters [aria-hidden], so the snapshot collapses to just the overlay's controls — a 146-ref page becomes ~10. Expected, not a crash: it hands you the open overlay, scoped. Tells: get count '[role=dialog]' is 1, and the trigger reads [expanded=true]. (A large modal like Color Info stays large — the collapse hides the background, not the modal's own content.)

Non-modal (transparent/none). The page stays fully in the snapshot (no aria-hidden, no role=dialog) — but the backdrop still blocks the pointer. This is the one that strands you: you see a background ref, click it, and get ✗ covered by <div.bg-overlay/50 …>. That means the overlay is open, not that the app is broken. Close it, re-snapshot, continue.

Exits (all six): press Escape, the visible Close button, or a real click outside the overlay:

agent-browser mouse move 80 840    # bottom-left, clear of the popover
agent-browser mouse down
agent-browser mouse up

The Dismiss in your snapshot is not a close button — it's react-aria's visually-hidden dismiss affordance (1px, tabIndex=-1, and a modal renders two of them), meant for screen readers. Clicking it by ref misses or hits whatever's under it. Use Escape or Close.

Never click the backdrop by selector. It aims at the element's center — under the overlay — so it clicks the overlay and silently does nothing.

Pick an area

Read the one file that matches. Each has: the seed URL, the flow as a step→drive→expect table, and what CI does not cover there.

Say	Area	Covers
"validate colors"	`references/colors.md`	add, select, rename, edit, randomize, color mode, reorder, remove, undo/redo
"validate scale"	`references/scale.md`	presets, curves, palette options, steps, variant, lock, per-color overrides
"validate palette"	`references/palette.md`	rename, views (List/Grid/Preview), gamut, sidebar, swatch copy, Share
"validate groups"	`references/groups.md`	assign groups, filter chips, filter retirement
"validate preview"	`references/preview.md`	live preview: collapse, theme cycle, tabs, color select
"validate export"	`references/export.md`	Export All + Export scale, formats, color formats, copy
"validate inspect"	`references/inspect.md`	charts, Color Info, Contrast Grid
"validate auth"	`references/auth.md`	login, save/update, My Palettes, favorite, load, delete
"validate spacing"	`references/spacing.md`	the four color-spacing modes
"validate mobile"	`references/mobile.md`	bottom bar, hamburger menu

Vague ask ("does the app still work?") → run colors then palette, and say that's what you did.

references/gaps.md lists what the e2e suite never touches — where manual validation is actually worth the time. Selectors there are not protected by a passing suite; snapshot before trusting them.

Reporting

Say what you drove, what you observed, and what broke.

A step you couldn't drive (control missing, selector dead) is a finding, not something to work around silently.

Don't claim a pass for a step whose observable you didn't check. If you didn't assert it, you didn't validate it — say so instead of inferring it from ✓ Done.

validate-ui

About

Validate the Color Lab UI

The loop

`✓ Done` is not a result

What the app is

Boot

Step zero: read the opening state, don't assume it

The three observables

The `eval` rule

Sliders

Option sliders → `focus` + `press`

Channel sliders → `setRange`

Never `fill` a slider

URL writes are not debounced

Selectors

Reading the clipboard

App-specific behavior

Overlays

Pick an area

Reporting

Use it

Manifest

Reviews

About

Validate the Color Lab UI

The loop

✓ Done is not a result

What the app is

Boot

Step zero: read the opening state, don't assume it

The three observables

The eval rule

Sliders

Option sliders → focus + press

Channel sliders → setRange

Never fill a slider

URL writes are not debounced

Selectors

Reading the clipboard

App-specific behavior

Overlays

Pick an area

Reporting

Use it

Manifest

Reviews

`✓ Done` is not a result

The `eval` rule

Option sliders → `focus` + `press`

Channel sliders → `setRange`

Never `fill` a slider