The React Native team you wish you had. A senior collective parachuted into apps that are on fire, or apps that need to be built right the first time. Series A/B startups only.
// when your code mounts us, the effect runs.import { useEffect } from "react";import { us } from "useffect.sh"; export function App() {useEffect(() => {// mounting elite squad…const ship = ;return () => ship.cleanly(); // no debt, full docs}, [us]);}We don't do retainers, sprints-as-a-service, or "audits" that end in a PDF. We do two things, and we do them at the level you can't hire full-time for.
"We unfuck the fucked code."
"We build the world a better app."
Every engagement leaves a measurable trace. Same app, same users, same metrics — before we mount, and after we unmount. Median across the last 8 rescues.
Six real engagements from the last four years. Clients you'll recognise, problems we owned, results worth showing.
Six months of contracted React Native on Le Chat. Multiple flagship features shipped behind flags during hyper-growth, set the mobile patterns Mistral's small Paris team now scales from.
Five Sephora staff codebases across Europe & Middle East folded into one monorepo. Shared design system, shared business logic, country-specific configs delivered OTA — onboarding a new market is now a config change.
Co-built the React Native template + primitive design system that powers Stadion's Premier League and rugby/tennis apps. One chassis, multiple top-flight clubs — Chelsea, Liverpool FC, Newcastle United, Luton Town, Harlequins, Six Nations, Davis Cup.
Multi-tenant Nx monorepo so 25+ credit unions get distinct branding and feature mixes from a single codebase. React Native Web unified mobile and web. New unions onboard with minimal engineering overhead.
Companion app for a PlayStation controller. Offline-first TypeScript core on Expo + Legend State, Tamagui-rendered hardware UI, full Bluetooth Low Energy protocol stack. Bridges silicon and React Native cleanly across iOS and Android.
Migrated Luko's RN app to TypeScript while keeping IoT smart-meter and BLE device flows live. Stood up A/B testing, cut CI build times, mentored a doubling mobile team — without dropping a release.
Six senior engineers. Different specialties, different years shipping, same standard. No juniors. No subcontractors. No bench. The squad that lands on your project is the squad on this page.
// the squad mounts together."dependencies": {"@useffect/david": "^10.2.0", // React Native · Expo · iOS · EAS · BLE"@useffect/gabriel": "^10.0.0", // React Native · Expo · monorepos · design systems · BLE"@useffect/jeremy": "^11.0.0", // React Native · TypeScript · Nest.js · Swift · Next.js"@useffect/ludwig": "^9.0.0", // React Native · Android · Redux · design systems · sport apps"@useffect/matthys": "^6.0.0", // React Native · Expo · EAS · TypeScript migrations · Twilio video"@useffect/pablo": "^8.0.0", // React Native · Swift · Kotlin · native modules · AI integration}
David Leuliette — Senior Mobile Engineer at useffect.sh. Specialties: React Native, Expo, iOS, EAS, BLE. Notable engagements: Sunday, Red Bull, AXA, NACON, Mahalo Banking, Smart Pension. npm scope: @useffect/david, version ^10.2.0.
Jérémy Magrin — Senior React Native Engineer · CTO at useffect.sh. Specialties: React Native, TypeScript, Nest.js, Swift, Next.js. Notable engagements: Mistral AI, Twenty, Betclic, Cookomix, Snoop Media. npm scope: @useffect/jeremy, version ^11.0.0.
Pablo Giraud-Carrier — Head of Mobile · Founding Engineer at useffect.sh. Specialties: React Native, Swift, Kotlin, native modules, AI integration. Notable engagements: The Mobile-First Company, Follow, YEGO, Privalia, vente-privee. npm scope: @useffect/pablo, version ^8.0.0.
Matthys Ducrocq — Head of Mobile · Co-Founder at useffect.sh. Specialties: React Native, Expo, EAS, TypeScript migrations, Twilio video. Notable engagements: Ekklo, weshipit.today, Filteroff, Karnott, Shoootin. npm scope: @useffect/matthys, version ^6.0.0.
Ludwig Vantours — Lead React Native Engineer at useffect.sh. Specialties: React Native, Android, Redux, design systems, sport apps. Notable engagements: Chelsea FC, Liverpool FC, Newcastle United, Luko, Cdiscount, Typology. npm scope: @useffect/ludwig, version ^9.0.0.
Gabriel Hofman — Senior Mobile Engineer at useffect.sh. Specialties: React Native, Expo, monorepos, design systems, BLE. Notable engagements: Sephora, Luko, TheFork, Meetic, Upstream (YC), Revyze. npm scope: @useffect/gabriel, version ^10.0.0.The whole engagement is a React lifecycle. We come in clean, do the work, and leave your team stronger than we found it — full docs, zero debt, the bus factor goes up when we go.
We sit with your code for 5 days. Profile it, fork it, break it, read the on-call docs. You get a written diagnosis with the three things that actually matter — not a 40-page audit.
We ship to your repo, in your branches, in your standups. Weekly demo on Friday. Numbers update on a shared dashboard. No dark rooms. No "almost done."
The hardest part of consulting is leaving cleanly. We write the runbooks, record the loom walkthroughs, train your on-call. If we did our job, you forget our names within a quarter.
Open source we maintain, bootcamps we run, meetups we organize. The work that isn't a SOW.
Early core contributor · 2 years freelance shaping foundational architecture · 224 commits
Expo module for native file previews — QuickLook on iOS, Intent chooser on Android
Cross-platform text data detection — NSDataDetector on iOS, ML Kit Entity Extraction on Android. Detects phones, URLs, emails, dates, addresses.
5+ years instructor · 450+ React Native engineers trained · 50+ conference talks
Co-organizer · Paris RN meetup · Bordeaux dev meetups · sourcing speakers and sponsors
Two slots open for Q3. If your app is on fire — or you're staring at an empty repo and a board deadline — talk to us this week.