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Senior React Native developer · Expo · iOS & Android

I ship apps that perform

React Native since it shipped in 2015. I help startups and scale-ups design, build and grow their mobile apps, from MVP to store release, all the way to fine-grained performance work.

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Portrait of Jérémy Magrin

80+engagements delivered

Available5.0 / 5

11 years

years of experience

80+

engagements delivered

5.0 / 5

freelance rating

500,000+

users across my apps

Trusted by

MWMOdisei MusicEpsorMistral AITwentySnoop MediaBetclic GroupCajooMon Spécialiste AutoCooknet (Cookomix)EDF Store & ForecastLuniNeliomon-marché.frZestBeJoe

How it goes

It starts with your idea

A workshop, specs, a scope. I say no to whatever does not need to exist in v1: that is what gets the app shipped.

The MVP ships in weeks

React Native and Expo, a base built to grow from the first commit. Lists, navigation, rendering: what gets expensive later is settled now.

Live on the App Store and Google Play

EAS builds, signing, store listings, over-the-air updates. And when a native API is missing from the ecosystem, I write the module myself, Expo or bare React Native, in Swift and Kotlin.

Or you arrive with an app that stutters

Lists that jank, a tab that freezes, a battery that melts. An inherited app, one that started badly, or one generated by AI: plenty of engagements begin here, not at step one.

A steady 120 fps, measured

At Odisei Music: a 40 to 50 % frame rate drop removed, CPU down 40 %, memory down 20 %. Before optimising, I measure.

120fps
40% CPU
20% memory

Your team takes over

Monorepo, shared design system, agentic tooling with guardrails, documentation. I leave when you no longer need me.

Recent work

What I have been building

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MWMMay 2026 → present

Software publishing

React Native developer

Design and build from scratch an Expo native module unifying MWM's Publishing and Advertising SDKs, making them available cross-platform for their clients.

React NativeExpo ModulesSwiftKotlinTypeScript

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Odisei MusicMay 2026 → present

Music / E-commerce

React Native developer - Performance specialist

Brought in as a React Native expert to optimise the mobile app's performance, with Android as the priority.

React NativeExpoPerformanceAndroidLegend List

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EpsorAug 2025 → May 2026

Banking & insurance

React Native developer

Design and roll out a web and mobile monorepo architecture, where the mobile app lived outside the existing monorepo and forced a package release for every shared change.

React NativeExpoNext.jsTurborepopnpm

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Mistral AIMar 2025 → Aug 2025

High Tech / AI · French unicorn

Mobile developer - React Native, iOS & Android

Grow the Le Chat mobile app with new flows and new native capabilities.

React NativeExpoSwiftKotliniOS

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TwentyJun 2023 → Mar 2025

Software publishing / Open source

Back-end and front-end developer - Nest.js, React.js

Build the back-end foundations of Twenty, the open-source CRM positioned as a modern, scalable alternative to Salesforce, with performance as a hard requirement.

Nest.jsGraphQLTypeScriptTypeORMReact.js

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Snoop MediaJan 2022 → Jun 2023

Social networks

CTO as a service - React Native, Nest.js

Lay the full technical and organisational foundations of Snoop, a social network for film and series recommendations, as CTO as a service.

CTOReact NativeExpoNest.jsManagement

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Tech stack

The tools I reach for

Coral marks what I use daily. The rest I bring in when the project calls for it.

Mobile

React NativeExpoEASTypeScriptExpo ModulesExpo RouterReact NavigationLegend List

Web

React.jsNext.jsTanStack QueryJotaiLegend StateZustandRedux ToolkitSolito

Back-end

Nest.jsPrismaPostgreSQLNode.jsGraphQLTypeORMDrizzleSupabaseFirebase

Native

SwiftKotlinModules natifsSDK iOS & AndroidObjective-C

Quality & delivery

CI/CDGitHub ActionsBunAgileTDDJestFastlaneRN Testing Library
Open source

I publish and I contribute

Open source is a real part of how I work: I publish my own libraries and I contribute regularly to third-party projects, maintaining them, patching them and pushing fixes through.

@magrinj/expo-quick-look

github.com/magrinj/expo-quick-look

Expo native module for file preview: QuickLook on iOS, Intent chooser on Android. 100+ formats, native rendering rather than a WebView, authenticated remote downloads, iOS markup and multi-file navigation.

Expo ModulesSwiftKotlinTypeScriptBunpublié sur npm

@magrinj/parse-ingredients

github.com/magrinj/parse-ingredients

Multilingual recipe ingredient parser. Quantities, fractions and units parsed then aggregated, six languages supported, zero runtime dependencies.

TypeScriptBunpublié sur npm

Expo library in progress

A new Expo module in progress, opening up a native API that the Expo ecosystem does not cover yet.

Expo ModulesSwiftKotlin

I am a regular on the React Native conference circuit: App.js Conf in Kraków, and React Native Connection in Paris next.

Notes

What I write between projects

Field notes on React Native, mobile performance and native modules. Published on LinkedIn first, archived here.

J'étais dans la salle à App.js quand Christian Falch a présenté la bascule de React Native vers SPM

Je vous parlais de la date il y a deux mois · Là c'est le plan de remplacement qui est posé, et il est plus malin qu'un grand soir où tout casse d'un coup · Il a ouvert la RFC #994, portée par Meta et Expo · Et Swift Package Manager arrive par phases · phase…

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Il a suffi d'écrire Additionally pour faire fuiter un repo privé

Noma Labs a révélé début juillet une faille sur les GitHub Agentic Workflows, ils l'appellent GitLost · Le scénario est bête à pleurer · tu ouvres une issue sur un repo public, n'importe qui peut le faire · dans le texte tu glisses une instruction pour…

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Si t'as déjà écrit un Web Worker, tu sais déjà faire du multithreading en React Native

Depuis 2015, un seul thread JS fait tourner ton app en entier · Parser un gros payload, hasher un fichier, filtrer une image · Tout ça se bat avec ton UI pour le même runtime · Ça bloque, ça saccade, et t'as appris à faire avec · react-native-workers vient de…

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All notes

Client feedback

Rated 5.0 out of 5 on freelance platforms

Parfait en tous points ! Jérémy a un excellent niveau technique, un souci du détail particulier, s'est très rapidement investi dans le projet, et a été très apprécié de toute l'équipe.
Félix · Twenty
À l'aide de ses compétences en React Native, Jérémy nous a permis de faire un saut qualitatif dans la qualité du code de notre application mobile. Il connaît le framework y compris ses parties immergées, et sait faire preuve de pédagogie pour former ses pairs.
Lancelot Blondeel · CTO
Jérémy was very professional and autonomous. He really tried to understand the needs and pays a lot of attention to details. The work was delivered on time and exceeding expectations.
Zhou · Axens
Travailler avec Jérémy a été un plaisir. De par sa pédagogie et son expérience, il m'a beaucoup appris. Très rigoureux et minutieux pour toujours produire un code propre. Je ne peux que le recommander !
Roman Cirier · Développeur front-end
Excellent travail. Jérémy est intervenu pour lancer le développement de notre plateforme de demandes d'optimisation de prévision de consommation en énergies renouvelables, à destination du marché américain. Les chiffrages étaient précis et le code produit de qualité.
Yann Lombard · Responsable pôle front-end
Jérémy est un dev 5 étoiles : code de qualité, délais respectés, très réactif, il trouve toujours une solution aux problèmes posés. Vous pouvez lui faire confiance les yeux fermés.
Manu B · Chef de projet, Cooknet
Background

Eleven years, same curiosity

Other engagements

Betclic GroupJul 2021 → Dec 2021

React Native developer

Built and launched Betclic TV, an international mobile app rolled out in Portugal and Poland: sports news, live scores and match streaming.

CajooJan 2021 → Jun 2021

React Native, Nest.js developer

Strengthened the Cajoo delivery app, since acquired by Flink: in-app payment and new features.

Mon Spécialiste AutoJan 2020 → Dec 2020

React Native developer

Full offline-first rewrite of the mobile app, fully usable with no connection, to make field vehicle inspections reliable. Trained the mobile developers.

Cooknet (Cookomix)Jan 2019 → Dec 2020

React Native developer

Built and continuously grew Cookomix, a high-traffic recipe app used by more than 300,000 people every month.

EDF Store & ForecastSep 2019 → Dec 2019

React.js developer

Statistical analytics dashboard for end clients, making consumption data easier to read and track.

LuniJun 2019 → Dec 2019

React Native developer

Mobile apps for the Luni studio: group features on the Calendrier app in Swift and ReactiveSwift, then the Omada app in React Native.

NelioMar 2019 → Jun 2019

React Native developer

Optimised and extended the Nelio fresh-produce delivery app, on both performance and user experience.

mon-marché.frJul 2018 → Mar 2019

React Native developer

Built a white-label mobile app from scratch for home delivery of fresh produce. Clean, scalable architecture and fast MVP delivery.

ZestSep 2018 → Nov 2018

React Native developer

Supported ZestMeUp: trained the teams on clean React Native development and set up a solid technical base.

BeJoeFeb 2016 → Aug 2018

Mobile lead - React Native

Led the mobile side of BeJoe, a recommendations social network: technical foundations laid from day one of the company, mobile team management, iOS and Android apps.

Before going freelance · iOS developer in Swift and Objective-C on Timi, a business management platform, fully autonomous on the mobile side · Full-stack and mobile developer at Tack (BuzzVillage) in Node.js and Cordova · Django web developer for Les Libraires, turning a brochure site into an e-commerce store · Software developer at Thales Avionics in C and C++, on an automated verification tool for embedded widget libraries · Software developer at Thales Raytheon Systems in Java, C and C++, on the full migration of the SkyView programme.

Get in touch

Got a project in mind?

Guaranteed reply within the hour, plus a free thirty-minute audit call.

Email meMaltLinkedIn

Emailcontact@magrin.fr

Phone+33 6 73 12 19 30

Based inParis, France · fully remote