Web App Development
Custom Web App Development When Off-the-Shelf Stops Working
We build custom web apps for businesses whose operations no longer fit Salesforce, Airtable, or Notion — tailored exactly to your workflows, built on a codebase you own entirely.
When Custom Web App Development Becomes the Right Choice
Off-the-shelf SaaS tools stop working when your business model stops fitting their assumptions. When Salesforce cannot model your sales process, when Airtable's relational model cannot handle your data complexity, when Notion's database cannot support your approval workflow, and when your team has built a parallel spreadsheet system to fill the gaps — custom web app development is the answer. The inflection point is different for every business, but the signs are consistent: you are paying for features you do not use, missing features you need, and losing hours per week to workarounds.
Custom web app development does not mean building from scratch in the expensive sense. At Greta, we start every project with battle-tested building blocks — authentication systems, payment infrastructure, database hosting, UI component libraries — so we are not solving solved problems. What we build custom is your business logic: the specific rules, workflows, data relationships, and automations that make your operations work. That is where the value is, and that is where we spend every development hour.
The biggest risk in custom web app development is scope creep: starting with a clear vision and accumulating features until the project is three times bigger than planned. We prevent this with a fixed Phase 1 scope document, a defined acceptance criteria list, and an explicit change order process for additions. Clients who trust this process ship faster and at lower total cost than clients who try to include every requirement in the initial build. We have seen this pattern dozens of times — the discipline is the product.
Our Approach to Custom web app development
Every project follows our 4-step vibe-coding process — AI handles the boilerplate, senior engineers handle the craft. From idea to live product in 3–7 days for MVPs.
Discovery
We identify the specific gaps in your current tooling that cost your team the most time or revenue. We map the exact workflows, data entities, and business rules that need to be encoded in the custom web app. Then we ruthlessly prioritize: what is the minimum set of features that eliminates the biggest pain points? That becomes Phase 1.
Design
Custom web apps need to fit the mental model of the people who use them daily — your team, not a generic user persona. We interview 2–3 key users during design, wireframe the workflows they actually perform, and validate the designs with those users before writing code. The best custom web apps feel obvious to use because they were designed around real workflows.
Build
Next.js 15 with TypeScript for the frontend and API layer, Supabase PostgreSQL for the data model, custom business logic in PostgreSQL functions and Next.js Server Actions, and Stripe if payment processing is needed. AI handles the scaffolding for standard patterns; our engineers implement the custom business rules that make this tool specific to your business.
Launch
User acceptance testing with the real users who will use the tool daily. We run through every workflow they perform and verify that the custom web app performs it correctly. Edge cases identified during UAT are fixed before go-live. We configure the production environment, migrate any existing data from spreadsheets or legacy tools, and provide a training session.
What You Get
Every custom web app development engagement includes these deliverables — scoped before we start, delivered before we invoice.
- Custom data model designed specifically for your business entities and relationships
- Business logic implementation: custom rules, workflows, calculations, and automations
- User-specific dashboards and views based on role, team, or data access level
- Data migration from spreadsheets, legacy tools, or existing systems
- Custom reporting and export tools for the metrics your business tracks
- Approval workflows and status tracking for multi-step business processes
- Integration with existing tools via webhooks or API (CRM, ERP, accounting software)
- Admin panel for configuration, user management, and data oversight
- User documentation and training session for primary users
- Full codebase handoff: Git repository, architecture docs, and deployment configuration
Tech Stack We Use
Custom web app development at Greta uses a pragmatic stack chosen for maximum development speed and long-term maintainability: Next.js 15 for the full-stack framework, TypeScript for type safety across all layers, Supabase PostgreSQL for the custom data model with RLS for access control, and Vercel for deployment. For business logic that is complex enough to benefit from database-layer enforcement — multi-step workflows, constraint validation, computed aggregations — we implement it in PostgreSQL functions and triggers rather than application code, because the database is always in sync while application code can be bypassed. Stripe is added when payment processing is required. The result is a custom web app that is genuinely tailored to your business while running on a stack your future developers will recognize immediately.
Case Study
PLGOS — Custom Activation Tracking Platform
PLGOS is the definition of custom web app development: a tool built specifically for product-led growth teams who needed activation tracking that existing analytics platforms could not provide. The existing tools — Mixpanel, Amplitude — tracked events but could not model the complex, customer-specific activation criteria that PLGOS's clients defined. We built a custom data model for activation criteria, event matching rules, and cohort comparison that no off-the-shelf tool could replicate. The custom web app became the founders' own product — sold to 340 paying customers who had the same gap in their analytics tooling. Built from scratch in 11 days on our standard stack.
Read full case studyPricing Transparency
Custom web app development starts at $5,000 for a tightly scoped MVP with one core workflow and a basic admin panel. Full custom platforms with complex data models, multi-user access control, integrations, and reporting run $15,000–$60,000 depending on business logic complexity. We scope Phase 1 precisely before starting — no vague estimates, no hourly billing, no surprises. You know the cost and timeline before we write a line of code.
MVP
From $5,000
3–7 business days
Full Build
From $15,000
2–4 weeks
All projects include full code ownership, two revision rounds, Vercel deployment, and one week of post-launch support. No hidden fees.
Frequently Asked Questions
How do you decide what goes in Phase 1 versus Phase 2?
Phase 1 includes the minimum set of features that eliminates the core pain point and delivers measurable value to real users. Phase 2 is everything that would be nice to have but does not block the primary workflow. We make this distinction explicitly during discovery and document it in the scope agreement — so both parties agree on what is in and out before development starts.
Can you replace our spreadsheets with a custom web app?
Yes. Spreadsheet-to-web-app migrations are one of our most common project types. We model the data from your spreadsheets into a proper relational database schema, build the forms and views your team uses to manage that data, import the existing data, and train users on the new system. The result is the same workflow but faster, more reliable, and accessible to multiple users simultaneously.
Do you integrate custom web apps with our existing tools?
Yes. Common integrations include HubSpot and Salesforce via REST API for CRM data sync, QuickBooks and Xero via API for accounting data, Slack and email via webhook for notifications, and legacy internal systems via CSV export/import if no API exists. We scope integrations individually — simple webhook delivery takes hours, bidirectional sync with a legacy system can take weeks.
How do you handle changing requirements during development?
Scope changes are handled via a formal change order process: we document the change, estimate the impact on timeline and cost, and get written approval before making any changes. This is not bureaucracy for its own sake — it is the mechanism that prevents projects from growing 3× without a corresponding 3× in budget and timeline. We are firm about this.
Can non-technical staff use the custom web app you build?
Yes — if we design it correctly, which we do. Every custom web app we build for internal use is tested with the actual users who will use it daily, not just the technical contact. If the primary users are non-technical staff, we prioritize clarity over flexibility in the UI and provide a training session as part of every project.
What if I need the custom web app to grow significantly?
We design custom web apps with the expected scale in mind — data model, indexing, and architecture are all sized for your growth trajectory. If you expect to go from 10 to 10,000 users in year one, we design for 10,000 users from the start. The custom web app we build will not require a rewrite to handle the scale you describe during discovery.
Can you add AI features to our custom web app?
Yes. AI features — document processing, natural language queries, content generation, intelligent classification — can be added to any custom web app that has a relevant data layer. We evaluate which AI features would deliver the most value given your data model and user workflows, and scope them as a separate engagement or include them in the initial build.
How long does custom web app development take?
A custom web app with one core workflow, basic user management, and a simple admin panel takes 1–2 weeks. Complex custom platforms with multiple workflows, integrations, advanced reporting, and a large data migration take 4–8 weeks. We give you a precise timeline during discovery — not a range, a specific date.
Ready to ship?
Ready to build your custom web app?
Start Your ProjectOr reach us directly at hello@greta.agency
Written by the Greta Agency team · Last updated April 2025