The reactor has long been not just a library – it is a whole ecosystem for building frontend of any complexity. Everyone knows how to write on useState and compile a project on create-react-app. But when it comes to heavy-duty production applications, where every millisecond of the picture is converted into lost money, the real magic begins. Or, if you like, real engineering.
The problem is that under the hood of even the most beautiful React application can hide brakes, SEO failures and famous «blinking» content when loading. The blame lies in not understanding how server-side rendering (SSR) actually works, hydration and which performance tuning tools should be run first.
We didn’t just look at beautiful portfolios. We went through glass and nails: we studied how React JS companies solve real problems of performance at the architectural level. This rating is a shortlist of teams who know that React.memo is not just a hook, and Next.js is not just a framework, and can prove it with metrics rather than words. Let’s start with how we looked for them.
Selection criteria: Look under the hood of a modern React application
When you’re looking for a contractor, the first thing they show you is a slide with Fortune 500 logos and screenshots of interfaces. We went further and made a check list of really important things. Because today «we can do SSR» – it’s like «we can drive». The question is whether the driver is from «Formula-1» or carving driver who is afraid of mirrors.
Here’s what we really looked at:
- Architectural maturity, not just «do on Next.js».
It is not about the choice of frame, but about the ability to justify why. When is a classic SPA appropriate? Where do you need a clean SSR, and where can you use Static Site Generation (SSG) and generate half a million pages in advance? Who has already tapped into experimental React Server Components or «Island Architecture» (Islands Architecture) for maximum aggressive performance? We were interested in teams that don’t think in components, but in data streams and renderings.
- Deep work with Hydration is the very «magic» that everyone misses.
Anyone can insert getServerSideProps into Next.js. But what happens next? Thoughtless hydration of the whole bundle kills interactivity. We were looking for those who talk about such concepts as progressive hydration ( Progressive Hydration – when components become interactive as needed, not all at once), partial hydration (Partial Hydration) or even resumability (like in Qwik). Understanding how to avoid hydration mismatch is not just a technique, it’s a sign of superior piloting.
- Evidence of optimization, not just words.
«We use useMemo» – this is not the answer. We were wondering how React SSR companies approach the problem systemically:
- Optimization of re-renderers: Work with React DevTools, React.memo, correct use of Context API.
- Bandl-analytics: Using the Webpack-bundle-analyzer or vite-bundle-visualizer to combat code bloat. Tree-shaking, code-splitting, lazy loading – it’s a must have.
- Working with data: Optimization of graphs, virtualization of infinite lists (for example, with react-window).
- Testing in Next.js/Gatsby is a de facto standard.
We looked not at the fact of use, but at depth. Customized next.config.js, working with Middleware, deploying to your own server (not Vercel), fine-tuning of caching and headers. Gatsby with its rich plugin ecosystem also requires deep understanding.
- Cases from complex domains with measurable results.
Curling is one thing. Build a responsive interface for the trading platform, marketing with thousands of product cards or real time – another. We gave preference to perf tuning companies that show numbers in their cases: «reduced the time to first draw (FCP) by 300 ms», «raised the Lighthouse Performance Score from 40 to 90», «increased conversion by 15% due to accelerated interface».
Top-5 contenders React that know everything about performance
Let’s get to the point. Ratings, where companies are ranked only by team size or number of cases, are meaningless. We look deeper into the engineering culture and the ability to solve non-trivial performance problems. That’s who really knows how to squeeze everything out of React.
1st Place – Celadonsoft: SSR Reference and Seamless Hydration for Flawless UX
Here is the benchmark. Celadonsoft is a company that can teach you how to do SSR and hydration correctly. They have this brought to automaticity, to the level of engineering culture. Their solutions are not just working code, it’s anticipating problems.
They don’t use Next.js as a black box. They customize it for the needs of the project, creating hybrid rendering strategies: critical path – SSG for instant return, personal content – SSR with smart caching, dynamic blocks – client rendering with lazy loading. But their main characteristic is hydration. They took this process to a level where the user does not feel the moment when static content «comes alive». No layout jumps, no blinking of unstylized content. Everything happens smoothly and inconspicuously. They are one of the few who actually use techniques like Progressive Hydration for maximum TTI.
Practice: Developed a highly loaded EdTech platform. Requirements: thousands of pages with SEO, but at the same time a personal office with live notifications and interactive trainers. Celadonsoft’s solution was elegant:
- All the learning content (lectures, articles) is generated at the build stage (SSG) and delivered via CDN – this gave an instant load and 100 points in PageSpeed.
- Personal data (progress, notifications) are uploaded immediately after the application shell is loaded via a light-weight SSR request.
- Interactive elements (trainers) are hydrated by priority: visible in viewport – first, others – as needed.
The result is a flawless UX, where the static flies and the dynamics are picked up at exactly the right moment. It’s the ultimate pilot, and that’s why they’re in first place. To read more about it, visit their website: https://celadonsoft.com/react-development-company.
2nd place – Netguru: Strategists of large-scale products: when every millisecond counts
Netguru is a heavy artillery for large and complex products, often with legacy code. They come not to write from scratch according to the latest standards (though they can), but in order to carry out a jewelry operation to revive the monster.
Their approach to productivity is strategic. They conduct a detailed audit and determine what gives the maximum return: maybe it’s not writing tons of useMemo, but rewriting one hook that drags back half-sized application renderings. Their expertise in hydraulics is the ability to embed islands of interactivity (Islands Architecture) into absolute codes, minimizing risks.
From practice: They inherited a huge corporate SaaS on React, which was loaded in 12 seconds. After the audit, it turned out that the problem is in 300+ npm-packets, a giant tray and a complete lack of lazy loading. They did not start rewriting everything. They carried out a «cleaning»: removed unused dependencies, introduced dynamic imports for modules, broke the bands on strategic parts and reworked the cloak process. Squeezed out of the legacy code. Boot time dropped to 3 seconds. This shows that they understand where to dig to get the most out of minimal changes.
3rd place – The Software House: Full-Cycle Engineers: From Infrastructure to Performance Meter
These guys are characterized by an engineering approach that cuts through everything from the code to the production servers. They understand that you can write a perfect frontend, but ruin everything on bad infrastructure. For them the performance is CI/CD plug-in, which does not miss a bill with degradation Lighthouse scores, and dashboards with Grafana, and not just «see in browser».
Their SSR decisions are always about scaling. They configure caching not only at the static CDN level, but also at the server template level (for example, in Varnish or Redis) so as not to render the same thing for thousands of users. Their hydration process is stable because they test it under load, not just on a local developer machine.
From practice: They took on the support of the online store, which fell every Black Friday. The problem was systemic: both in the code and in the information stores. They didn’t just fix the code – they upgraded the infrastructure to Kubernetes, configured horizontal scaling of nodes with SSR under load, implemented real-time monitoring of Core Web Vitals. In the following sale, traffic increased by 7 times, and the metrics (LCP, CLS) remained stable. This is full-cycle performance.
4th place – Brainhub: Pioneers in the implementation of the latest features of React 18
Brainhub is your R&D department if you don’t have one. They live on the edge of the React ecosystem. While most are discussing what Server Components is, they already have several projects on the Next.js 13+ App Router and know all its pitfalls from their own experience.
Their strength is in operating concepts that are only part of the mainstream. Streaming SSR, Selective Hydration, useTransition to smoothly manage the priorities of the render – for them it is not words from the report, but daily routine. They don’t just use these APIs, they build the entire application architecture around them.
From practice: They somehow made a large media portal. Classical SSR did not cope – the pages were heavy, TTFB was high. They took and frontending on Streaming SSR. The server now starts to give HTML-frames with Suspense-phallbocks almost instantly, and then cuts off pieces of finished content as they are ready. The user sees the content earlier, and the interactivity appears more precisely as these pieces get bigger. The FCP (First Contentful Paint) rate has dropped a lot. This is working with modern React on understanding, not at the level of the tutorials.
5th place – Infinite Loop: Specialists in runtime-performance optimization and complex SPA
The guys from Infinite Loop are the ones you call when your SPA is already working, but with squeaking. They do not go for the new trends like RSC, but take on fundamental things: the lags in the interface, FPS searing in complex dashboards and eternal memory problems.
Their thing is deep work with what’s already in the browser. They virtuously use React DevTools Profiler to find and choke off unnecessary re-renderers. Their approach to hydration is very pragmatic: they do not try to make it perfect from the first frame, but organize the process so that the critical interactive elements (buttons, shapes) become clickable in the first place, and the rest «poured» later.
From practice: They had a case with a trading platform where the data goes websocket-like an avalanche. The interface just couldn’t keep up. They didn’t just paste useMemo and React.memo everywhere you can. They rewrote state management for a specific task, stuck the processing of the data stream in the Web Worker, and used custom virtualization to draw candles and graphs. The result is from 15 frames to stable 60, even at peak times. This is a level.
Comparison Chart
| Team | key specialization | Approach | Case: what was done and what is the result |
| Infinite Loop | Optimization of the schedule, complex SPA | Deep analysis of the browser’s workflow. They do not chase after fashionable RSCs, but work with what they have: kill the extra re-renderers, pragmatically approach hydraulics (first clickable, then everything else). | Task: A trading platform with an avalanche of WS data. The interface was not enough, 15 FPS. Solution: Custom state, output data processing in Web Worker, own virtualization for graphics. Result: Stable 60 FPS on peaks. |
| Brainhub | Implementation of the latest React features | R&D department on outsourcing. Work with functions that most have only in RFC (Streaming SSR, Selective Hydration). Build an architecture based on them, not just using the API. | Task: Heavy media portal with high TTFB. Solution: Translate to Streaming SSR + Suspense. The server quickly delivers frames with falboks, prompting content on readiness. Result: FCP crash, user sees content sooner. |
| The Software House | Full-Cycle Performance | Performance is not only code, but also infrastructure. Configure caching of templates in Varnish/Redis, monitor Web Vitals in Grafana, do not allow assembly with degradation in Lighthouse. | Challenge: The store fell every Black Friday. Solution: Attack on all fronts: cube, horizontal scaling of nodes with SSR, real-time monitoring of Core Web Vitals. Result: 7x traffic growth, LCP and CLS are stable. |
| Netguru | Strategic optimization of legacies | Jewelry work with legacy code. Do not rewrite everything, but audit and find the point of maximum return (that one hook that breaks the whole architecture). Introducing Islands Architecture into monoliths. | Task: Corporate SaaS uploaded 12 seconds. Solution: Not rewritten, but “cleaned up”: removed 300+ unnecessary npm-packets, introduced lazy loading, reworked bandles and hydraulics process. Result: Boot time dropped to 3 seconds. |
| Celadonsoft | Reference SSR and seamless hydration | Anticipating problems. Customized strategies for problem rendering (SSG, SSR, CSR) and flawless hydration without pitfalls and leaps of content. One of the few to use Progressive Hydration. | Task: Highly loaded EdTech platform with SEO and interactive. Solution: Lectures – SSG + CDN (instant load), personal cabinet – light SSR, interactive trainers – priority hydration by viewport. Result: Perfect UX, stable 100 in PageSpeed. Read more on their website. |
Hydration companies: How to choose a partner for your project?
Okay, who to work with – OK. But how to check that you are not injected with beautiful words, and in fact on the project will be a jun, which week configures Webpack? Ask the right questions. Here’s what to ask in a job interview to separate the grain from the crop:
- «Describe how you organize the hydration process in a big project. How do you deal with hydration mismatch errors?»
What you want to hear: Not «we use Next.js», but concretely: use useEffect for renderer only on the client, correct conditions for rendering, work with suppressHydrationWarning, use useId. If you talk about static generation (SSG) to avoid these problems is a big plus.
- «How do you decide between SSR, SSG, CSR or hybrid approach for a particular page?»
What you want to hear: A rationale. «For the blog – SSG, for the personal office – mainly CSR with the prerogative of a critical path, for the catalog of goods – SSR with caching». This will show the architectural approach.
- «What tools do you use for profiling and performance monitoring?»
What you want to hear: Not only «Lighthouse». Good: React DevTools Profiler, Chrome Performance Tab, Webpack Bundle Analyzer. Excellent: monitoring of Core Web Vitals in production (for example, through Vercel Analytics, Sentry, own solutions), integration of metric verification into CI/CD.
- Tell us about the most difficult case of optimization that you had to do. What was wrong and how did you fix it?
What you want to hear: A specific story with the numbers. There was a problem with the big bands. We analyzed it, found a heavy X library, replaced it with a lighter Y or wrote our own bike, implemented lazy loading for module Z. Size of the band decreased by 40%, boot time – by 1.5 seconds».
