Next.js AI applications
Next.js AI app development, tested and costed before launch
We add AI assistants, document search and agents to the Next.js app you already run. Answers are tested on your data, the running cost is estimated before build, and your engineers stay on the roadmap.
For CTOs, product leads and founders with a Next.js product and an AI feature to ship
- Free 30-minute call
- Paid pilot you can stop
- You own the code
What Next.js AI app development means at HorizonLux
By the HorizonLux engineering team · reviewed by Seif Sgayer, Founder · updated 30 Sep 2026
Next.js AI app development at HorizonLux means adding AI features to a company's Next.js product, tested on its data and costed before build, for CTOs, product leads and founders. The work covers a streaming assistant, a RAG chatbot over company documents that shows its sources, an agent that works through the product's own APIs with a person approving risky steps, and extraction from files and forms.
Senior engineers write the code in your repo, behind your auth, through pull requests your team reviews, with model calls kept on the server and deployment on Vercel or your own servers. The published proof is RepairCheck, a vehicle damage inspection product in Germany, where HorizonLux built AI damage analysis with OpenAI vision, a copilot that writes to the case record, and a Next.js admin dashboard with prompt configuration for the AI.
Work starts with a free 30-minute call with Seif Sgayer, the founder, then a paid pilot with one agreed deliverable that you can stop if it does not land. Price and length are agreed on the call. You own the code, the IP and the docs.
HorizonLux at a glance
- Company
- HorizonLux, a software and AI engineering company
- Based in
- Tunisia; works with clients in the UK, UAE and EU
- Founded
- 2020
- Delivered by
- Senior engineers only, in English, in any timezone
- Engagement
- Free 30-minute call, then a paid pilot with one agreed deliverable
- You own
- The code, the IP and the docs, all in your repo
- Published proof
- RepairCheck (Germany): AI damage analysis, a copilot and a Next.js admin dashboard
What Next.js AI app development puts in your repo
A Gartner article from January 2026 says at least half of generative AI projects were abandoned after proof of concept by the end of 2025, because of poor data quality, weak risk controls, rising costs or unclear value. So next to the feature, you get one control each for wrong answers, cost and risk.
The AI feature itself
The assistant, document search, agent or extraction your users need, inside the screens they already use. We also build what it depends on: schema changes, API routes, background jobs and permissions.
Next.js App RouterVercel AI SDKPostgresOpenAI · Claude
An eval set, before the UI
Real questions your users ask, the source each answer should use, and a pass rule, written with your team. It runs on your data before launch and on every pull request, and you see every result.
- A cited answer, or a plain 'not sure'
- Low-confidence cases go to a person
- Re-run whenever the model changes
A cost model, before build
Cost per conversation from prompt size and model price, multiplied by your expected volume, so finance sees a monthly figure before the full build starts. Once live, every request logs its tokens and cost.
- Prompt caching where it pays
- Smaller models for simple steps
- Budgets and alerts in production
Guardrails and security
Model calls and API keys stay on the server. Retrieval returns only what the signed-in user may see, and prompt-injection attempts sit in the eval set.
- Rate limits per user
- A person approves an agent's risky steps
- A fallback model if a provider fails
Stack and hosting, checked 30 Sep 2026: Next.js 16.3 on Node.js 20.9 or later, AI SDK 7, Postgres, and OpenAI or Claude models, on Vercel or your own servers. Vercel functions run for up to 300 seconds by default, and up to 800 on Pro and Enterprise, so agent runs that need longer move to a background job.
Beyond the model: what shipping AI at RepairCheck taught us
Five design choices from building RepairCheck that we bring to new Next.js AI work.
A demo has to answer one question well. A product has to handle the awkward cases, put the result where people already work, and step aside when a person owns the decision.
At RepairCheck, much of what makes the AI useful sits around the model. Your feature gets those decisions agreed in writing before the build starts.
Write to the record, not a chat window
RepairCheck's copilot writes to the case record. Output kept in your data can be reviewed and reused; output left in a chat gets copied by hand.
Decide where the AI stops
RepairCheck's auto-estimates stop once an expert claims a case. We agree your handoff rule before build and test it in the eval set.
Tune prompts where the product is run
RepairCheck's Next.js admin dashboard holds the prompt configuration, so the AI can be adjusted there, not only in the codebase.
Keep a trail you can check
The same dashboard keeps audit logs, so when someone asks what happened to a case, there is a record to show.
Design the capture, not only the prompt
RepairCheck's mobile app captures each case through a guided photo flow and voice notes. Input captured well is easier for any model to read.
Shipped AI and Next.js work you can check
RepairCheck is the one AI project we have published, so we say plainly what it shows and what it does not. What it cannot show, the paid pilot tests on your own data before you commit.
RepairCheck
AI features · GermanyVehicle damage inspection. We built the mobile app with its guided photo flow, AI damage analysis on inspection photos with OpenAI vision, the copilot, WhatsApp booking and n8n flows. It is vision and copilot work, not document search.
OpenAI vision · React Native/Expo · n8n · WhatsApp
Read the RepairCheck case studyRepairCheck dashboard
Next.js · admin dashboardThe admin dashboard behind the product, built in Next.js, with prompt configuration for the AI, audit logs and partner management. It is our one published Next.js client project; this website also runs on Next.js.
Next.js · React · Node · Postgres · Recharts · Tailwind
See the dashboard in the case studyMasterPilot
Delivery record · not AIThe operations portal of a flight-training platform, built in React and NestJS: not Next.js and not AI. It shows how we deliver over time. Client-verified: 10 releases from Dec 2024 to Jun 2026, 129 endpoints and 23 modules, live since March 2026.
React · NestJS · Postgres · Prisma
Read the MasterPilot case study
…how much ownership he takes: he thinks a feature through, raises edge cases before they turn into bugs, and delivers something that actually works… Exceptional clear and consistent communication.
How we build Next.js AI applications: our engineers write, yours review
Four steps, each with something you can check. You see results on your own data before you commit to the full build.
- 01No commitment
Free 30-minute call
Tell Seif Sgayer the feature, the data behind it and what a wrong answer would cost you. If a simpler, non-AI fix would do the job, Seif will say so.
You get · A clear view on fit and, if it fits, a pilot scope
- 02One deliverable
Paid pilot on your data
Agreed up front; pilots usually take CONFIRM: typical pilot length. For example: a thin working slice of the feature in your repo, tested on your real data and costed at your volume.
You get · A one-page readout: eval results, cost and a go or stop
- 03Weekly demo
Build through pull requests
Work lands in your repo as pull requests, checked by your CI, with the evals running on each change. Every week you get a demo and a written update on answer quality and cost.
You get · A feature your users can use, and a written record of each week
- 04
Handover
Budgets, alerts and logging go live. Your engineers get docs, runbooks and training on prompts, evals and cost logs.
You get · A feature your team can run and re-test without us
Price and length are agreed on the call. There is no promise of results: the pilot exists so you can stop if it does not land.
Tested and costed, on one page: a sample pilot readout
Each pilot ends with a readout like this one, written for your feature and your data. The figures below are for a made-up help assistant in a SaaS product.
| Line | Sample entry | Why it is there |
|---|---|---|
| Eval set | 60 questions taken from support tickets, each with the source it should use and a pass rule | It tests what users actually ask, in their own words |
| Eval result | 51 pass, 3 hand off to a person as intended, 6 fail | Every failure gets a cause and a planned fix before the full build |
| Main cause | 5 of the 6 failures cite a retired pricing page | Here the fix is in the documents, not the model |
| Tokens per conversation | About 6,000: system prompt 1,500, retrieved passages 3,000, question and history 1,000, answer 500 | It shows where to cut. The system prompt is the same on every call, so it can be cached |
| Monthly volume | 20,000 conversations, taken from product analytics | Cost grows with volume, so the number comes from real usage, not a guess |
| Monthly running cost | 110 million input and 10 million output tokens, priced at the list rates of two candidate models, with and without caching | Finance sees a range before the full build starts |
| Call | Go, once the retired pages leave the index | A plain go or stop, with the reason in writing |
Sample figures, not client data. For rough numbers on your own feature, try our token counter and prompt caching calculator.
Adding AI features to an existing Next.js app: four ways, compared
Four realistic routes, judged on what a CTO weighs: fit, roadmap impact, time to start and life after launch.
| What matters | HorizonLux | Your own engineers | A new AI hire | A freelancer |
|---|---|---|---|---|
| Suits you when | You want one AI feature shipped and your team kept on the roadmap | The feature is core to your product and the team has room | AI will be a long-term product line | The task is small and clearly defined |
| Effect on your roadmap | Your team reviews pull requests and a weekly demo | Roadmap work moves to make room | Your leads hire, onboard and manage | You scope, manage and review the work |
| Evals and a cost estimate before launch | Part of the pilot readout | If the team has done it before | Depends on who you hire | Depends on the person |
| Time to start | Once a pilot scope is agreed on the free call | When someone frees up | After a hiring process | Often quick |
| After launch | Handover with docs, runbooks and training | Your team runs it | The new hire runs it | Depends on their availability |
| Code and IP | Yours, in your repo | Yours | Yours | Yours, if the contract says so |
| How you pay | A pilot, then a build, priced on the call | Salaries you already pay, plus delayed roadmap work | A salary, plus hiring and management time | Hourly or fixed price |
A general comparison, not a review of any firm or person. If your own team or a hire suits you better, we will say so on the call.
Questions about Next.js AI app development
Direct answers to what CTOs and product leads ask before the call.
Can you add AI features to our existing Next.js app?
Yes. We work inside your current repo, auth, database and deploy setup, through pull requests your team reviews, so the feature lives where the rest of your product lives. If the app runs an older Next.js version, we check early whether the feature needs an upgrade and, if it does, scope the upgrade in. If the feature started as a v0 prototype, we move it into your codebase rather than running it on the side.
Is Next.js good for AI apps?
Yes, for AI features inside a web product. Route handlers and server functions keep model calls and API keys on the server, answers stream to the screen as they are written, and the Vercel AI SDK gives one interface across OpenAI, Anthropic and other providers. It is widely used: 20.8% of respondents in the Stack Overflow 2025 Developer Survey use Next.js. Heavy machine learning, such as training your own models, fits better in a separate service. For AI work outside a Next.js product, see our AI development services.
Which LLM should we use, and can we switch later?
The one that passes your eval set at a running cost you accept. In the pilot we run the same questions through more than one OpenAI or Claude model and compare quality, speed and cost per conversation; simple steps often suit a smaller model. Because we build with the Vercel AI SDK, switching later means a configuration change, prompt tweaks where needed and an eval re-run. A fallback model can cover a provider outage. Before any real data is sent, we go through each provider's data settings with you.
Do you build AI agents, or only chatbots?
Both. An agent calls your product's own APIs as tools, and a person approves any step that is hard to undo, such as a refund or a data change. We also say when a fixed workflow would do the job instead: Gartner predicted in June 2025 that over 40% of agentic AI projects will be cancelled by the end of 2027. Agent runs longer than your hosting allows move to a background job.
How do you stop a RAG chatbot over company documents from making things up?
We instruct it to answer only from your documents, show its sources and say it does not know when nothing relevant is found. Nobody can promise zero wrong answers, so we measure them: evals check your real questions against the expected source before launch and on every change. When the model is unsure, or a person owns the decision, the case goes to someone on your team. In McKinsey's State of AI trust in 2026, 74% of respondents called inaccuracy a highly relevant AI risk.
How much does Next.js AI app development cost?
Price is agreed on the free call, once the feature is scoped. We do not publish prices, because a chat assistant over clean documents and an agent across five internal APIs are different jobs. You start with a paid pilot with one agreed deliverable, not a full build. Running cost is separate: conversations × tokens per conversation × model price. Our token counter, prompt caching calculator and RAG cost calculator give rough numbers now; the pilot gives a figure at your volume.
How long does it take to go from AI prototype to production?
It depends on the feature and the state of your data, so length is agreed on the call; a pilot usually takes CONFIRM: typical pilot length. The order does not change: a paid pilot on your real data that ends in a one-page readout, then the build through pull requests with a demo and a written update every week, then handover with docs, runbooks and training. Real data comes early, because ten hand-picked demo questions say little about the thousandth real one.
Who owns the code, and who keeps it patched after launch?
You own the code, the IP and the docs, including prompts and eval sets, all in your repo; NDA on request. After handover your team runs it, or we agree upkeep on the call: CONFIRM: patching commitment. Upkeep matters here: npm shows AI SDK versions 5, 6 and 7 shipped between July 2025 and June 2026, and a critical React Server Components flaw (CVE-2025-55182), disclosed in December 2025, hit Next.js 15 and 16 App Router apps until patched.
Bring the AI feature your roadmap has no room for
Thirty minutes with Seif Sgayer, our founder, on the one AI feature you most need to ship. No commitment.
Book a Free 30-Minute Call
Bring the feature, and the prototype if there is one. Seif goes through where it sits in your Next.js app, which data and permissions it needs, where a person should take over, and what it could cost to run. You leave knowing whether a paid pilot is worth it.
Don’t want a call? Email [email protected]
Book a free call- A starter list of eval questions for your feature
- The main cost drivers at your volume
- What the pilot and its readout would cover
We worked with Seif on the React Native app for our vehicle-appraisal platform. What stood out most was how much ownership he takes: he thinks a feature through, raises edge cases before they turn into bugs, and delivers something that actually works. And then there is one more thing why I wanted to work with Seif after our very first call: Exceptional clear and consistent communication. It is a pleasure to work with him and his team!
Michael EmaschowFounder, RepairCheckFree 30-minute call
30 minutes · Google Meet · Free
No packages, no sales pitch. You leave with a clear first step.
- 30 min
- Google Meet
- Calendly
- No commitment
- The plan is yours to keep
- Built for teams at Tabeebi, RepairCheck and MasterPilot
HorizonLux is an independent company. Next.js, Vercel, v0, React, OpenAI, Anthropic, Claude, n8n and WhatsApp are trademarks of their owners. No partnership or endorsement is implied.
