The Agentic AI App Builder That Builds, Checks, and Ships Your App
NEXUS AI is an agentic AI app builder: describe an app, and the agent writes the code, runs checks, fixes errors, and deploys it to your own cloud.
An agent, not a one-shot generator
Each request runs as an agent loop. The model lists and reads project files, writes and edits them, installs npm packages, and runs project checks, then reads the errors and fixes them before it answers. The agent works on every supported provider: Claude, GPT, Gemini, and Grok. For full-stack Next.js apps, a development sandbox runs the real application with its dependencies and a database, so checks run against the actual app instead of a static mockup.
Pick the model, or bring your own key
Choose Claude, OpenAI, Google Gemini, or xAI Grok, plus OpenRouter and custom OpenAI-compatible endpoints. Free includes a limited managed model selection, and paid plans unlock all supported managed models. Add your own supported provider key and turns on that key do not use the plan's managed AI token budget. Daily request limits are separate from tokens; see the pricing FAQ for both allowances.
A code editor with full ownership
Every generated file is yours to read and change in the Monaco-powered Code tab: create, edit, delete, search and replace, and save with Cmd or Ctrl plus S. Undo and redo work per file, Discard changes resets a draft, and each saved change becomes a checkpoint you can undo from the save notice or restore later. Syntax errors are flagged, and clicking one jumps the cursor to the failing line.
Build from the terminal with NEXUS CLI App Builder
Run nexus builder to start an app or resume the project saved in the current checkout, including from a subfolder. Choose your AI with /provider and /model in chat or dev mode. Run local commands and interactive editors with /run, capture a failing check with /run --capture, and ask /fix --last-run for a local draft. Review with /diff, test with /rerun, then /accept or /reject. Captured checks and drafts survive restarting, and resuming reuses your files without another pull.
Upload files or import a repository
Start from what you already have. Upload up to 20 files (500 KB each, 2 MB per upload) into a new or existing project. The builder detects each file type, checks its syntax, previews plain HTML pages instantly, and can ask the AI to fix a file with errors. Code already on GitHub can be imported as a repository.
Visual iteration with a live preview
Attach a design reference or paste an image into chat, select an element in the preview, and describe the change. The instant browser preview handles fast interface work, while the development sandbox runs forms, server routes, installed packages, and database-backed behavior.
Deploy the app and everything it needs
Deploy from the builder header. NEXUS AI builds a container, provisions managed Postgres when the app stores data, attaches S3-compatible storage for uploads, and injects STRIPE_SECRET_KEY from the encrypted Secrets Vault for payments. Run it on NEXUS AI or in your own cloud account (Google Cloud on Starter; AWS, Google Cloud, and Azure on Pro). Share a frozen snapshot link, let others remix it, or push the code to GitHub.
How it works
- Describe the app in plain words, pick a starter idea, upload files, or import a GitHub repository.
- Choose Claude, GPT, Gemini, or Grok, or your own API key, and let the agent write the files, install packages, run checks, and fix errors.
- Review the live preview, click an element or attach a design image to change it, and edit any file in the Code tab with undo and syntax checks.
- Share a snapshot link or push to GitHub, then deploy to NEXUS AI or your own AWS, Google Cloud, or Azure account with a database, storage, and secrets.
Apps people build with the agent
| App | Example prompt | What gets set up |
|---|---|---|
| Booking site | A booking site for my hair salon with services, time slots, and an admin view of appointments | Next.js pages and a Prisma schema for services and bookings; managed Postgres on deploy |
| Sales dashboard | A sales dashboard with revenue by region and month, a filterable deals table, and CSV import | Charts, an import route, and a database for deals |
| Client portal | A portal where my agency's clients log in, see project status, and upload files | Authentication, per-client pages, and an S3-compatible bucket for uploads |
| Online store | A small shop with a product catalog, cart, and Stripe checkout | Product pages, a checkout route, and STRIPE_SECRET_KEY from the Secrets Vault |
| Internal tool | An inventory tracker for our warehouse with stock alerts and a history of changes | CRUD pages, a change log table, and deployment into your company cloud account |
| Marketing site | A coffee shop site with a menu, opening hours, and a contact form | Responsive pages with instant preview, ready for a custom domain on Starter |
AI App Builder plans
| Plan | AI models and tokens | Where apps run | Team |
|---|---|---|---|
| Free, $0 | Selected managed models; 500K managed tokens a month and 5 AI requests a day; supported own keys | 1 deployment on NEXUS AI, for testing | Just you |
| Starter, $29/month | All supported managed models; 5M managed tokens a month and 10 AI requests a day; supported own keys | 2 deployments on NEXUS AI or Google Cloud Run, custom domain | 3 members |
| Pro, $149/month | All supported managed models; 20M managed tokens a month and 30 AI requests a day; supported own keys | 5 deployments, up to 10 concurrent containers, AWS, Google Cloud, and Azure, rollback | 10 members |
| Enterprise, custom | Unlimited AI tokens on any provider | Your cloud account or on-premises, SSO | Unlimited |
NEXUS AI vs Lovable and Replit Agent
| Capability | NEXUS AI | Lovable | Replit Agent |
|---|---|---|---|
| Builds from chat with a live preview | Yes, as an agent that runs checks and fixes errors | Yes | Yes |
| AI models | Claude, GPT, Gemini, or Grok, or your own API key | Lovable's built-in agent | Replit's built-in agent |
| Pricing | Flat plans with an AI token budget: $0, $29, $149 | Credits: $0, or $25 to $50 for 100 monthly credits | Free Mode within its allowance; paid Agent work uses effort-based credits |
| Where the app runs | NEXUS AI or your own AWS, Google Cloud, or Azure account | lovable.app hosting on Lovable Cloud | Replit-managed infrastructure |
| Backend | Always-on containers, workers, PostgreSQL, MySQL, MongoDB, or Redis | Edge functions and scheduled jobs on Lovable Cloud | Autoscale or Reserved VM deployments with a separate production database |
| MCP server for AI agents | 74 tools, each gated by an OAuth scope | Full access to every project the account can reach | 8 tools to create, update, and publish apps |
Research sources
Frequently asked questions
What is an agentic AI app builder?
An agentic AI app builder uses an AI agent that carries out the work in steps instead of returning one block of generated code. In NEXUS AI, the agent reads and writes project files, installs packages, runs checks, reads the errors, and fixes them before it answers, and the finished app deploys from the same workspace.
What is the NEXUS AI App Builder?
The NEXUS AI App Builder is an agentic full-stack development workspace. It builds apps from chat, lets you inspect and edit every file in a built-in code editor, previews the interface in the browser, verifies full-stack changes in an isolated development sandbox, and deploys the finished app on NEXUS AI or in your own cloud account.
Which AI models does the builder use?
Supported Claude, OpenAI, Google Gemini, and xAI Grok models, plus OpenRouter and custom OpenAI-compatible endpoints. Choose from the models currently available in the provider menu. Free has a limited managed selection; paid plans unlock all supported managed models. Grok and OpenRouter require a paid plan.
Can I bring my own API key?
Yes. Add a Claude, OpenAI, or Gemini key under AI Providers on any plan, or a Grok or OpenRouter key on a paid plan. Turns on your own key are billed by that provider and do not use the plan's managed AI token budget.
Is the AI App Builder free?
Yes. Free includes selected managed models, 500K managed AI tokens a month, 5 AI requests a day, and one deployment for testing. Starter ($29 a month) includes 5M tokens, 10 requests a day, a custom domain, and NEXUS AI or your own Google Cloud account. Pro ($149 a month) includes 20M tokens, 30 requests a day, and your own AWS, Google Cloud, or Azure account. Own cloud resources and own API-key usage are billed separately by those providers.
Can I edit AI-generated code directly in the browser?
Yes. The Code tab lets you create, edit, and delete project files in a Monaco-powered editor with syntax highlighting, search and replace, per-file drafts, undo and redo, and Cmd or Ctrl plus S saving. Each saved change creates a checkpoint you can undo, and syntax errors jump the cursor to the failing line.
Can I use the AI App Builder from the terminal?
Yes. Install the NEXUS CLI and run nexus builder. It resumes the current checkout, or offers New app and Resume project outside a checkout. Use /provider and /model to choose AI, /run for local commands or editors, and /run --capture to save test output. Review AI drafts with /diff, test with /rerun, and /accept or /reject them before sharing changes. Drafts and captured commands survive a restart. Deployment remains an explicit command.
Can I upload my own files to the builder?
Yes. Upload up to 20 files at a time, 500 KB each and 2 MB per upload, into a new or existing project. The builder detects each file type, runs a syntax check, previews plain HTML pages, and can ask the AI to fix files with errors. Syntax errors warn but never block the upload.
Does the AI Builder test the code it generates?
Yes. The agent can run project checks inside the development sandbox, inspect errors, change files, and repeat verification. If the sandbox is unavailable, it falls back to static reasoning and reports that limitation.
Can agencies use it to build apps for clients?
Yes. Build the app, send the client a share link to a frozen preview for sign-off, then push the code to GitHub or deploy it into a cloud account the client controls. Starter includes 3 team members and Pro includes 10.
Can I build from a screenshot or edit a specific element?
Yes. You can attach design mockups or screenshots for the AI to inspect, then select an element in the preview and send its context back to chat for a targeted change.
Can Claude, Cursor, or Codex send an app to the builder?
Yes. MCP-compatible clients can use nexusai_builder_push to send files into a builder session and receive a preview URL. After browser-side edits, nexusai_builder_pull returns the current files to the conversation.
Can the builder deploy apps with Postgres, file uploads, or Stripe?
Yes. Builder deployments can provision managed Postgres. When generated code uses file storage or payments, the deploy flow can attach an S3-compatible bucket and inject STRIPE_SECRET_KEY from the encrypted Secrets Vault.
How is it different from Lovable or Replit Agent?
All three build apps from chat. NEXUS AI lets you choose the model or bring your own key, edit every file in a built-in editor, and deploy the app as a standard container on NEXUS AI or into your own AWS, Google Cloud, or Azure account. Lovable hosts apps on Lovable Cloud, and Replit Agent publishes on Replit-managed infrastructure.
About NEXUS AI
NEXUS AI is an agentic AI app builder and full-stack deployment platform. Explore the AI App Builder, learn more on the About page, read the documentation, or contact the team through nexusai.run/contact.
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