React.js web development agency

React.js web development agency in Athens.

TWENTYONE is a React.js web development agency in Athens. We build websites, web platforms and e-commerce in React and Next.js, written from zero for the brand they belong to — 19 years of custom web development, and no templates in any of it.

Why React

Why React.js web development

React is how interfaces are built now. It keeps what the screen shows in step with what the data says, it assembles every page from components that are built once and reused everywhere, and it is the most widely known way of building for the web in the world. Meta, Netflix, Airbnb, Shopify and Atlassian build with it.

For a client, the strongest argument for React.js web development is not technical. A React codebase can be picked up by a competent developer anywhere. What we hand over is yours to keep, to extend, or to take to somebody else — the opposite of a platform you rent and cannot leave.

And because the interface is made of components rather than pages, a React product gets cheaper to change as it grows. A change to a button is a change to every button; a new page is assembled from parts that already work.

What we build

React, from the landing page to the platform

Custom websites
Brand websites designed and written for the brand, rendered with Next.js so they arrive as finished HTML, load fast on a phone and are read in full by search engines and AI crawlers.
Web platforms
Booking engines, dashboards, portals and internal tools — the interfaces where state, permissions and real-time data make React earn its place.
E-commerce
Bespoke e-commerce with its own checkout, integrated in real time with the ERP, warehouse, accounting and courier systems a business already runs.
Rebuilds and rescues
A slow theme, a page builder, a React app nobody on the team understands any more. We take it over, measure it and rebuild what needs rebuilding — not more.
One design system
The same components behind the website, the platform and the app, so the brand looks and behaves the same everywhere it appears.

The stack

React.js web development with Next.js, TypeScript and a real back end

React draws the interface; Next.js decides how each page reaches the browser — rendered ahead of time, per request, or regenerated in the background as the content changes. That choice is made per route, which is where most of a site's speed and nearly all of its search visibility are won or lost.

Behind the interface sits the back end. Our Node.js web development team builds the API, the accounts and the integrations in the same language as the front end, over a PostgreSQL database, typed end to end in TypeScript — so the form in the browser and the server agree on what a valid order looks like.

When the product needs an app, the same React knowledge carries over. React Native app development shares the types, the logic and the design tokens with the website, so the app is a second client of a system that already works rather than a second project.

Speed and search

Fast by construction, readable by search

The performance work that is usually an expensive afterthought is the default in a Next.js build: images sized and converted automatically, fonts subset and preloaded, JavaScript split so each page ships only what it runs. A performance budget is agreed before design starts and enforced in the build.

Search follows from that. Every page arrives as complete HTML with its own title, description and structured data, so it can be indexed properly — and cited in AI answers — rather than hoped for. React.js web development done this way is not a trade-off between a rich interface and SEO; it is both.

How we work

How a React.js web development project runs

Briefing
You tell us what you are building, what exists already and what is in the way. We reply within two working days — with questions, or with the honest answer that you do not need us.
Blueprint
Scope, architecture, the stack and a fixed plan, agreed before a line of code is written. You know what is being built, in what order and why.
Build
Designed and built in React and Next.js by the same people, in Athens. Working software every week or two, on a staging address you can open, rather than a reveal at the end.
Launch and after
Release, monitoring and a named team that stays. The code, the design files and the data are yours.

The record

A React.js web development agency trusted with demanding briefs

19 years of work for brands including COSMOTE, Piraeus, Avène, MARKET IN, SCORPIOS, TRVL AIR and NEXTCOMMERCE — telecoms, banking, pharmacy, retail, travel and hospitality. Different categories, one discipline: the engineering is the same wherever the brand is.

The same studio designs, builds, photographs and films, so the interface and the imagery inside it are decided together rather than negotiated between two suppliers.

Common questions

What does a React.js web development agency do?
It designs and builds websites and web applications with React, the JavaScript library for user interfaces created at Facebook. TWENTYONE, in Athens, builds custom websites, web platforms and e-commerce in React and Next.js, with a Node.js and PostgreSQL back end.
Why build a website in React instead of WordPress?
A React and Next.js site is written for the brand rather than assembled from a theme and plugins, so it loads only what it uses, is rendered as finished HTML for search engines, and has no plugin stack to update or break. It is also open source and hireable anywhere, so the client is not tied to one vendor.
Is React good for SEO?
Yes, when it is rendered on the server. Next.js delivers each React page as complete HTML, so search engines and AI crawlers read the content without running JavaScript. A React app rendered only in the browser is the case that causes SEO problems.
What is the difference between React and Next.js?
React is the library that draws the interface. Next.js is the framework around it that decides how each page is rendered and delivered — ahead of time, per request or in the background — and adds routing, image optimisation and server code. TWENTYONE uses both together.
Can you take over an existing React project?
Yes. TWENTYONE takes over React and Next.js codebases, audits them, and continues the work — refactoring what slows the team down rather than rewriting what already works.
Do you work with clients outside Greece?
Yes. TWENTYONE is based in Athens and works in English with clients in Greece and abroad; the briefing, the plan and the weekly builds all happen remotely when they need to.

Initiate the blueprint

Tell us what you are building.

The stack, the timeline, the thing that is currently in the way. We reply to every briefing within two working days.

Honestly? You’re going to regret switching tabs.

Finding top-tier custom developers who actually care about your business scale is nearly impossible.

We are the best at what we do, and we’ve got the track record to prove it. Don’t waste time and money with second-best options.

You convinced me.
Let’s talk!