Caching nobody can explain
A page shows yesterday’s price, another refetches on every request, and nobody knows why. We write a rendering and cache rule for every route.
Next.js products that rank, load fast and stay secure
Diffco builds Next.js applications: marketplaces, SaaS products, content-heavy sites and admin consoles. We also take over the ones that have outgrown their first architecture. Senior engineers decide what renders on the server, what is cached and where the security boundary sits; AI agents build inside those rules; a person checks every key flow in a real browser before it ships.
Senior engineers. App Router and TypeScript by default. Discovery in days; working pages in weeks.
Products we developed are used by
Awards and client reviews
- Top AI Development Company
- Top 10 Software Developers
- Top AI Developers
in California
- Top Software Development Company
Diffco turned our concept into a polished product from scratch, delivering on a tight timeline. Clear communication, organized project management, and a strong mix of creativity and technical expertise produced an app that exceeded our vision.
Mason MeninCo-founder at WYA Group, Inc.Their commitment to excellence ensures our platform remains robust and adaptable to our evolving needs. With their expertise, we've successfully enhanced our offerings, making our collaboration highly effective.
Pete GualfettiHead of Design and Integration at Good2GoWe were impressed by Diffco's approach to the development process and how they engineer new solutions. They look ahead, learn about your product and strategy, and develop sophisticated, highly functional solutions.
Stas TushinskiyCEO & Co-founder at InstreamaticDiffco supplied us with the skilled engineers we needed to meet our ambitious goals. Their account manager proactively addressed concerns, ensuring our expectations were met.
Razvan SpatariuSenior Software Engineering Manager at MultiverseDiffco took on a complex financial system build for us — the kind of work that touches fund accounting and compliance, where there’s no margin for error — and they delivered. They helped us shape our AI product strategy rather than just executing tickets. Real ownership of the outcome.
Adam HooksCEO at Vero K12Diffco handled discovery for two complex health tech AI products for us. They’re technically sharp, honest about what’s actually worth building, and easy to work with. They moved fast without cutting corners and understood the healthcare space. Highly recommend.
Mark MagazuPrincipal at M3 Veterinary Innovation AdvisorsDiffco's expertise and engineering approach increase the reliability and efficiency of our IoT infrastructure. Diffco has proven to be a reliable partner with exceptional expertise. I highly recommend their services.
David C ThompsonSenior Digital Initiatives director at ChemTreatThe quality and consistency of the team make Diffco stand out from other vendors.
Art DanielovCEO at FlashgridThey were communicative, consultative, and helpful. They went above and beyond all the way. What an amazing team. I will work with them again and again.
Don MarklandCEO at Accountability Now
Where Next.js apps go wrong
Next.js makes the first page easy.
The hundredth page is where the shortcuts show.
Most problems come from decisions nobody made early: what’s cached, what runs where, who sees what, and when to upgrade.
Security in the wrong layer
Access checked only in the proxy (formerly middleware) or the browser. Miss one server action and data leaks. We check access where the data lives.
Server and client mixed up
Secrets in a client component, a whole page marked “use client” for one button, server logic shipped to every phone. We draw the boundary first.
Stuck on the Pages Router
Half the app on the App Router, half on the Pages Router: two data models, two sets of bugs. We move it route by route until one router is left.
Hosting costs nobody profiled
Every page rendered on demand, images reprocessed on every deploy, functions that run too long. We find which routes cost the most and fix those first.
Upgrades that keep slipping
Each major version changes caching, async APIs or defaults. Teams pin an old one, and patches become emergencies. We upgrade in scoped slices.
Decided before the first page
Prices, permissions and anything that touches money are computed on the server and enforced again where the data lives, not only in the proxy. Every page has a written rendering and caching rule, so “why is this stale?” has one answer.
Next.js development services
From a first marketplace to a platform search engines and customers both trust
New Next.js products
Marketplaces, SaaS apps and customer portals on the App Router and React Server Components, with rendering, caching and the security model decided in discovery.
Best for:Founders launching where speed and SEO matter.
SEO and content platforms
Marketing sites, catalogs and content hubs with static and incremental rendering, structured data and a headless CMS editors can run without engineering.
Best for:Companies whose traffic starts in search.
Admin consoles and internal tools
Staff panels with role-based access, tables, maps and reporting, sharing one data layer and one access model with the customer app.
Best for:Ops teams tired of filing engineering tickets.
Migrations and upgrades
Pages Router to App Router, older Next.js to the current release, Create React App or a custom SSR setup to Next.js, in slices, with the site live throughout.
Best for:Teams stuck halfway through a migration.
AI features on the web
Chat and assistant surfaces, streaming responses and server-side model calls, with prompts, keys and costs kept off the browser.
Best for:Teams adding AI their users can trust.
Choosing the framework
Next.js, React with Vite or Astro: which one fits?
React with ViteAstroNext.js
Best whenThe app lives behind a loginThe site is mostly content
Public pages and an application in one product
Public pages and an application in one productServer rendering and SEONeeds extra setup✓ Static by defaultStatic, incremental or dynamic, even within one page
Static, incremental or dynamic, even within one pageData and security on the serverA separate APIEndpoints and Actions; thinner for appsServer Components and server actions
Server Components and server actionsInteractivity✓ FullIslands of interactivityFull
HostingAny static hostStatic host, or a server adapterVercel, Node.js or Docker on any cloud
Typical riskWeak SEO for public pagesOutgrown by app-like featuresCaching and server/client boundaries without an architecture
We’ll recommend against Next.js when a plain single-page app or a content site will do the job for less.
How we build
Senior engineers decide the architecture. AI agents build the pages. A person checks every one before release.
Our own AI delivery platform puts your plan, your design system and your Next.js rules in front of every agent before it starts: what renders on the server, how each route is cached, which data may reach the browser. It checks everything it produces on every change.
Senior engineers decide what to build and how; more than 100 AI agents per engineer build inside those rules around the clock. Before release, a person watches each key flow work in a real browser and signs off against a standard agreed before the code existed.
The loop, on a Next.js product
- You say what the page must do, and who must never see it
- We show the routes, data and rendering rules it touches
- You approve a clickable version before it’s built for real
- Agents build inside the plan, with a check on every change
- A person checks it in a real browser and signs off
- 100+AI agents per engineer, directed by senior engineers
- Every changechecked against the plan, the tests and the rendering rules
- Every routehas a written rendering and cache rule
- One planroutes, data and access agreed before the build
What you get
A Next.js product that stays fast, secure and yours
A security boundary that holds
Access enforced where the data lives, no privileged keys in app code, so one bug in a page isn’t enough to expose another customer’s records.
Rendering rules, written down
Each route’s rendering mode and cache rule in the repo, so a stale page or a slow page is a lookup, not an investigation.
Speed and SEO checked in CI
Core Web Vitals budgets, metadata and accessibility checks run in CI. A page that gets slower or loses its title doesn’t ship.
Code and hosting you own
TypeScript throughout, tests beside the code, deployable to Vercel or your own cloud, with the plan, rules and decision log as plain files in your repo.
Why teams choose Diffco for Next.js
Engineers who have built full Next.js products, not just demo URLs
We’ve built a full marketplace in seven weeks
Vitality Access: two Next.js 15 apps on React 19 and Supabase, with row-level security as the access boundary, built at half the first estimate.
We’ve built Stripe payments that can’t charge twice
For Vitality Access: Stripe hosted Checkout, with an idempotent webhook as the only write into a paid state, verified against Stripe test mode.
We’ve built inside a client’s Next.js product
For Maze, we delivered the AI Moderator inside its own React and Next.js codebase, scope by scope, through its pull-request review.
We’ve built the management portal on top of field data
RepoScore’s Next.js admin console runs territory maps, role-based access and team reporting over data from three vendor systems.
We tell you when Next.js is the wrong tool
A dashboard behind a login may not need server rendering; a brochure site may belong on a CMS. We say so before you spend.
Senior team, in your time zone
The engineer who designs your rendering and data architecture is the engineer who ships it, in Pacific time, with an office you can visit.
End-to-end build · Healthcare marketplace
A full medical-tourism marketplace on Next.js, built in seven weeks at half the budget
Vitality Access connects patients in the US and Canada with vetted clinics abroad. Diffco defined the product and built both apps, a customer marketplace and a staff admin, on Next.js 15 and React 19, sharing one Supabase project. Prices are computed on the server, row-level security is the access boundary, and a single idempotent webhook moves a booking into a paid state.
- 7 weeksof development, for a scope that typically takes 3–4 months
- 2× lowerbudget than the first estimate, with nothing the business runs on cut
- 2 apps, 1 access modelcustomer marketplace and staff admin on one Supabase project
Two ways to start
Audit what you have, or hand us the build.
Next.js audit
One to two weeks. A senior front-end architect, with agents reading the whole codebase, maps rendering and caching per route, checks the server/client boundary and access control, profiles Core Web Vitals and hosting cost, and delivers ranked fixes with an estimate given as a range.
Fixed price, agreed up front- Every finding ranked, with its fix and its effort
- The report is yours. Use it with any team, including your own
Build with Diffco
Discovery in a few days to two weeks; a clickable walkthrough within the first weeks; working pages soon after. Senior engineers decide, agents build inside the plan, a person signs off in a real browser. Monthly team allocation or a fixed scope after discovery.
- Estimate given as a range with its open questions
- The plan, access model and design system are yours from week one
- Handover with runbooks and a codebase you can read
What we bring
Our Next.js stack, from the database to the browser
Framework
Next.js
TypeScript
React
Data and auth
PostgreSQL
Supabase
Prisma
tRPC
UI and content
Tailwind CSS
shadcn/ui
Radix UI
Storybook
Figma
Hosting and quality
Vercel
AWS
Docker
Sentry
Playwright
Vitest
Lighthouse CI
Payments, messaging and AI
OpenAI
Anthropic
AI SDK
Stripe
Twilio
Our case studies
AI interview moderator for user research, in production in 20 languages
Core engineering team behind Gitcha's product
One performance KPI system for field agents, built from multiple data sources and AI analytics
Full-stack engineering and AI product discovery for Happier, a top 3 meditation app in the world
Core platform support and development for a keyless-access startup
Explore our
amazing case studies
Let’s build something
great together.
Frequently Asked Questions
Because rendering, caching and security are decided before anything is built. Senior engineers set those rules; AI agents build inside them; a person checks each key flow in a real browser before release.
Next.js when public pages need search traffic, when server-side logic should stay off the browser, or when one product mixes marketing pages and an app. Plain React with Vite when everything sits behind a login. We decide in discovery and write the reason down.
Yes. Both routers can run side by side, so we move route by route, starting where Server Components pay off most, with the site live throughout. We finish the migration rather than leave you with two models.
Each route gets a rendering mode, a cache rule and a Core Web Vitals budget. CI checks them on every pull request, and a page that gets slower doesn’t ship. Fixes are measured before and after, on real traffic where possible.
Access is enforced where the data lives (row-level security, server-side checks), not only in the proxy (formerly middleware) or the browser. Secrets stay on the server, and every server action is treated as a public endpoint, because it is one.
No. Vercel is often the fastest path, with a preview environment for every change. Next.js also runs in Docker on AWS, Google Cloud or Azure; we compare cost and operational effort in discovery and pick with you.
Yes. Major versions change caching, async APIs and defaults, so we scope each upgrade first (what changes, what breaks, what the tests cover), then move in slices, and set up checks so security patches can land quickly.
Yes. We start with a short audit (rendering, caching, access control, test coverage, hosting cost), then fix, refactor or rebuild route by route while the product stays live. That includes apps generated with AI builders and never hardened.
An audit takes one to two weeks. Vitality Access’s marketplace and admin took seven weeks of development; larger platforms ship in usable releases, with a clickable walkthrough in the first weeks.
You do: the code, the access model, the infrastructure and the plan, rules and decision log, kept as plain files in your repo from the first commit and yours to take to any team.
Engagements start with a fixed-price audit or discovery, agreed up front. Builds run on a monthly team allocation or a fixed scope after discovery, with the estimate given as a range and the open questions that make it wide.
Need other services?
React DevelopmentSenior React engineers build fast, accessible front ends: new products, takeovers and React 19 upgrades.
Node.js DevelopmentSenior engineers build Node.js APIs and real-time services in TypeScript, and take over the ones that have grown hard to change.
Vibe Code RescueYour Lovable, Bolt, Replit or Cursor prototype worked. Our senior engineers stabilize, harden or rebuild it for production.
Web DevelopmentModern websites and web apps engineered by senior teams directing AI agents.
AI & ML DevelopmentML, RAG, computer vision, and copilots, engineered to production standards with Production-Ready AI Engineering.
Custom Software DevelopmentWeb apps, platforms, and internal tools, built in weeks instead of months, from PoC to production.
