SaaS product frontends
Multi-tenant dashboards, admin consoles, billing portals, and customer-facing apps on Next.js 15 App Router with RSC. SSR for SEO-relevant marketing surfaces, client rendering for app shells, Server Actions for mutations.
Services
React.js Development Services for US & EU SaaS
Senior React engineering for funded SaaS, fintech and AI products. We ship on React 19 with the React Compiler, TypeScript 5.6 strict, Next.js 15 App Router or Vite 6, and design systems on Radix UI + Tailwind 4. Teams are based in the EU on CET hours with a 4-hour US East-Coast overlap, sign GDPR DPAs, and ship to WCAG 2.2 AA. Dedicated teams from 12,000 EUR/month per engineer slot; fixed-scope sprints from 25,000 EUR.
React is the default frontend stack for US and EU SaaS, but the gap between "we use React" and "we ship a fast, accessible, maintainable React product" is enormous. We close that gap. Our engineers have shipped React in production since the class-component era — through hooks, Concurrent Mode, Server Components, and now the React Compiler — and we use that history to make boring, correct architecture decisions instead of chasing whatever was tweeted last week. Whether you need a greenfield product from a Figma file, a design-system rebuild on top of Radix and shadcn/ui, or a rescue mission on a Redux codebase that has outgrown its team, the engagement looks the same: senior engineers, weekly demos, measurable Web Vitals, and code your team can own when we leave.
What we build with React
Design systems & component libraries
Token-first design systems on Radix UI primitives, Tailwind CSS 4 with @layer composition, Storybook 8 visual review, and Chromatic regression testing. Shared across web, mobile-web, and Electron surfaces.
Data-heavy product UI
Virtualised tables with TanStack Table v8, charts on Recharts or Visx, real-time grids over WebSocket, and complex form flows on React Hook Form 7 + Zod 3 schemas shared with the backend.
Migrations & rescues
CRA → Vite or Next.js, Webpack 4 → Turbopack, Redux → TanStack Query + Zustand, Enzyme → React Testing Library + Vitest. We migrate incrementally behind feature flags — no big-bang rewrites.
Performance & Core Web Vitals
INP, LCP and CLS audits with field RUM data, route-level code splitting, Suspense boundaries, image pipelines on AVIF/WebP, and Lighthouse CI budgets in GitHub Actions that block regressions on PR.
Accessibility & i18n
WCAG 2.2 AA conformance with axe-core in CI, VPAT documentation for US federal procurement, EAA-aligned audits for EU launches, and i18n on next-intl or react-i18next with ICU MessageFormat and RTL support.
React stack we use in production
React 19
React Compiler
TypeScript 5.6
Next.js 15 App Router
Vite 6
Turbopack
React Server Components
Server Actions
TanStack Query v5
TanStack Table v8
TanStack Router
Zustand 4
Jotai
React Hook Form 7
Zod 3
Radix UI
shadcn/ui
Tailwind CSS 4
Storybook 8
Chromatic
Vitest
Playwright
React Testing Library
MSW 2
Turborepo
pnpm workspaces
Sentry
Vercel
Cloudflare Pages
axe-core
How a React engagement runs
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01
Discovery & audit
Week 1: codebase walk-through, dependency audit, bundle analysis with rollup-plugin-visualizer, Core Web Vitals baseline from CrUX field data, and a written report with quick-win backlog.
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02
Architecture & tokens
Weeks 2–3: decide routing model (App Router vs Vite SPA), state shape, design tokens from Figma Variables, folder layout, lint and type-check baselines, and CI gates.
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03
Build in 2-week sprints
Senior engineers ship features behind LaunchDarkly or Unleash flags, daily PR review, Storybook for visual sign-off, demo every Friday, deploy to preview on every PR via Vercel or Cloudflare.
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04
Handover & ownership
ADR documentation, onboarding video for your engineers, 30-day support tail, and a clean Git history. You own the IP, the secrets, the domains, and the codebase from day one.
Engagement models
Dedicated team
Long-term React squad embedded in your roadmap: senior engineers, a tech lead, QA, and design-system specialist. Your Jira, your standup, your release calendar. From 12,000 EUR/month per engineer slot.
Project sprint
Fixed-scope, fixed-price build: design-system bootstrap, feature module, migration sprint, or rescue engagement. 4 to 12 weeks, weekly demo cadence. From 25,000 EUR per sprint.
Staff augmentation
Single senior React engineer plugged into your team for 3–12 months, full-time on your stack, your PR review, your on-call. CET hours with US overlap. From 9,500 EUR/month per engineer.
All engagements include NDA, GDPR DPA, IP assignment, and EU-based payroll. No outsourcing to third countries without written approval.
Related work
LegalTech · Mobile · CRM
Signatory Pro
Native iOS and Android e-signature clients with a Symfony + React CRM for a cross-border law firm — KYC onboarding and a defensible evidence trail for US & EU matters.
Social Media · Consumer Tech
JoyJet
Production social platform — App Store + Google Play, live across the US and EU — with geo Radar, encrypted messaging and a virtual economy.
PropTech · Marketplace
ANT
Property marketplace web platform with listing CMS, search and B2B admin console for US and EU operators.
Why US & EU teams pick YuSMP for React
GDPR-aligned · ISO 27001 ready · SOC 2 Type II in progress
Senior-only React engineers
Median 8+ years of React in production. Every engineer has shipped at least one design system and one Core Web Vitals turnaround. No bootcamp hires staffed on your account.
Accessibility & compliance ready
WCAG 2.2 AA by default, EAA-aligned audits for EU launches, Section 508 VPAT for US federal RFPs, and axe-core wired into CI so regressions never reach main.
CET hours with US overlap
EU-based engineers working 9 AM–6 PM CET with a guaranteed 4-hour overlap with US East Coast. English-only async-first communication on Linear, Slack, and Loom.
We bill in EUR and accept USD; invoices are issued by an EU entity for clean tax handling, and engineering work is performed inside the EU under standard employment contracts — no third-country subprocessors without your written approval.
Frequently asked questions
Which React version and toolchain do you standardise on in 2026?
New apps go on React 19.0 with the React Compiler enabled in opt-in mode, TypeScript 5.6 in strict mode, and Vite 6 for SPA bundling. For SSR and edge rendering we default to Next.js 15 App Router with React Server Components and Server Actions. For very large product surfaces we run Turborepo monorepos with pnpm workspaces. We avoid CRA (deprecated) and Webpack-only setups in greenfield work, and we migrate Webpack 4/5 projects to Vite or Turbopack as part of modernisation engagements.
How do you handle state management and data fetching at scale?
Server state lives in TanStack Query v5 with suspense boundaries and granular invalidation, never in Redux. Client state goes to Zustand 4 or Jotai for cross-tree atoms; Redux Toolkit only when a client requires it for legacy reasons. Forms use React Hook Form 7 with Zod 3 schemas shared between client and server. For real-time we use TanStack Query subscriptions on top of WebSocket or Server-Sent Events, with optimistic updates and rollback. This stack typically removes 30 to 50 percent of boilerplate from Redux-era codebases.
Do you build design systems or work inside an existing one?
Both. For greenfield SaaS we build a token-first design system on Radix UI primitives, shadcn/ui patterns, Tailwind CSS 4 with CSS-layer composition, and Storybook 8 for visual review. For clients with an existing Figma library we wire Figma Variables to design tokens via Style Dictionary and ship the React component layer to match. All components ship with WCAG 2.2 AA contrast checks, keyboard navigation, and screen-reader labels — required for EU public-sector procurement and US Section 508.
How do you keep Core Web Vitals green on data-heavy React apps?
We treat LCP, INP, and CLS as engineering SLOs, not marketing metrics. INP is the hard one in React: we audit hydration cost, move heavy work to useDeferredValue and startTransition, and split routes with React.lazy plus Suspense. For image-heavy product UIs we use AVIF/WebP via the Next.js Image component or unpic-img with responsive srcset. We measure in production via web-vitals 4.x posting to a real-user monitoring sink (Sentry, Vercel Analytics, or Datadog RUM) and gate PRs on Lighthouse CI budgets in GitHub Actions.
Are your React engineers compliant with EU GDPR and US accessibility law?
Yes. All engineers are inside the EU under GDPR-aligned employment contracts; we sign a DPA with every client and act as data processor. We avoid sending PII to US-based analytics by default and prefer EU-region hosting (Vercel Frankfurt, Cloudflare EU isolation, Hetzner). For accessibility we follow WCAG 2.2 AA (mandatory under European Accessibility Act from June 2025) and Section 508 for US federal contracts. We run axe-core in CI and ship VPAT documentation when the client needs it for procurement.
What does pricing look like for a React engagement?
Two models. Dedicated team starts at 12,000 EUR/month for a senior React engineer + part-time tech lead and scales linearly — typical SaaS team is 3 React engineers, 1 design-system specialist, 1 QA, 1 tech lead at 38,000 EUR/month. Fixed-scope project sprints start at 25,000 EUR for a 4-week build (design-system bootstrap, feature module, migration sprint). All pricing includes CET workday with 4-hour US East-Coast overlap, English-only async communication, and weekly demo cadence.