Shipping Faster Without Breaking UX
15 Jan 2025 · 6 min read
Release features weekly—without slow pages, visual jumps, or broken flows. This guide shows practical guardrails for performance, accessibility, and rollout so speed doesn’t come at the expense of user experience. Shipping Faster Without Breaking UX
When this matters
What stays safe
Core flows, performance budgets (LCP/INP/CLS), accessibility minimums (WCAG-AA), and analytics remain intact through every sprint.
What’s at risk
Large PRs, hidden visual changes, regressions shipped to 100% of users, and “fix it later” debt that compounds quickly.
Quick checklist (do these)
- Ship small slices behind feature flags (no “big bang” PRs).
- Define UX acceptance criteria per story (empty, error, slow states).
- Enforce performance budgets (LCP/INP/CLS) and block regressions.
- Keep a WCAG-AA smoke suite for critical flows.
- Canary/gradual rollouts with instant kill-switch.
- Monitor real-user metrics (web + mobile) and alert on deltas.
1) Slice work & write UX acceptance
Break features into vertical slices that can ship independently. For each slice, specify success states plus empty, error, and slow network states. Review these during PRs and demos.
// Example (story) As a visitor, I can submit the contact form. Acceptance: - Fields labeled, keyboard accessible, visible focus - Error messages are inline & announced (aria-live) - Success toast & server retry on network hiccup - LCP ≤ 2.5s, INP ≤ 200ms, CLS ≤ 0.1 on mid device2) Gate changes with feature flags
Merge early, release late. Keep new UI and logic behind flags so you can test safely and turn off instantly if needed.
// React / Next.js
const enabled = flags.use("newCheckout");
return enabled ? // Android (Kotlin)
val enabled = remoteFlags.getBoolean("new_onboarding", false)
startActivity(if (enabled) NewOnboarding() else LegacyOnboarding())
3) Keep performance budgets automatic
Run Lighthouse CI (web) and app-startup checks (mobile) in CI. Fail builds on meaningful regressions.
# .lighthouserc.json (excerpt)
{
"assert": {
"assertions": {
"performance": ["error", {"minScore": 0.9}],
"categories:accessibility": ["warn", {"minScore": 0.9}],
"uses-optimized-images": "error"
}
}
}4) Accessibility smoke tests for critical paths
Validate semantics, focus, labels, and color contrast on sign-in, checkout, and forms.
// Playwright + axe-core (web)
await page.goto("/checkout");
await injectAxe(page);
await checkA11y(page, "#main", {
runOnly: { type: "tag", values: ["wcag2a", "wcag2aa"] }
});5) Roll out gradually
Ship to internal users, then 1-5%, 10-25%, and 50% cohorts while watching metrics. Keep a kill-switch and a rollback plan.
// Pseudocode
if (user.id % 100 < 10) enable("new_ui"); // 10% cohort
track("experiment:new_ui", { enabled });6) Watch real-user metrics
- Web: LCP, INP, CLS by route and device class
- Mobile: cold/warm start, frame time, crashes, ANRs
- Funnels: step drop-offs; alert on significant shifts
// Example web RUM snippet (INP)
new PerformanceObserver((list) => {
for (const e of list.getEntries()) sendToAnalytics("INP", e.interactionId, e.duration);
}).observe({ type: "event", buffered: true });Common pitfalls
- Monolithic PRs that mix UI, logic, and refactors
- Visual regressions from untracked CSS overrides
- Unannounced focus loss and keyboard traps
- Shipping to 100% without telemetry or a kill-switch
- Ignoring real devices / network constraints
Do we need feature flags for everything?
Use flags for user-facing changes, experiments, and risky refactors. Small internal fixes can ride the train without flags.
How do we keep pages fast as we add features?
Budget by route, code-split, lazy-load non-critical UI, optimize images/fonts, and monitor real-user metrics per release.