Web App Development
Web App Development for Agencies That Want to Own Their Tools
We build client portals, white-label platforms, and internal operations tools for digital agencies — multi-tenant from day one, branded for your clients, shipped in 2–3 weeks.
The Agency-Specific Challenges in Web App Development
Agencies building client portals face a specific technical challenge that product companies do not: the same codebase needs to power multiple clients with completely different branding, content, and user sets. White-labeling is not just a CSS theming exercise — it is a multi-tenancy architecture decision that affects how you store client data, how you handle authentication across organizations, and how you deploy updates across dozens of instances without breaking anyone. We have built agency client portals that are genuinely multi-tenant from day one.
Project management and client communication are the biggest sources of efficiency loss for growing agencies. When client status updates live in email threads, revision requests arrive through Slack DMs, and deliverable approvals happen over phone calls, you are losing 30–40% of billable efficiency to coordination overhead. We build internal web apps for agencies that centralize project workflows, automate client notifications, and give clients a self-service portal for revision requests and approvals — so your team spends time on work, not status updates.
Reselling web apps to your own agency clients creates a recurring revenue opportunity and a technical responsibility. If you are building white-label tools for your clients — reporting dashboards, SEO audit platforms, content calendars — you need a billing architecture that supports sub-licensing, usage metering per client, and client-specific feature flags. We have built reseller SaaS platforms for agencies and know exactly which architectural shortcuts create expensive problems at scale.
Our Approach to Web app development for agencies
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 map your client portfolio, the workflows your team performs for each client type, and the data each client needs to see in their portal. We ask: what are your clients asking for that you cannot give them right now without manual effort? The answer defines the portal scope and the admin tooling you need to run it efficiently.
Design
Agency client portals need to feel premium — your clients judge your capabilities partly by the quality of your own tools. We design client portals with your agency brand, not Greta's, and with UX patterns that make clients feel in control without requiring constant hand-holding. The admin side is designed for your team's efficiency, not for showcase.
Build
Multi-tenant architecture with Supabase Row Level Security ensuring client A never sees client B's data, white-label theming via database-stored brand configuration per tenant, role-based access control for client contacts with different visibility levels, and an agency admin panel for creating and managing client workspaces. AI handles the multi-tenant scaffolding; our engineers build the workflow automation.
Launch
We test multi-tenant isolation rigorously: log in as client A, verify that client B's data is invisible. We test role permissions at every access level. White-label theming is validated across all client-facing pages. We deploy to Vercel with a custom domain setup for your main agency portal, then configure subdomain routing for each client workspace.
What You Get
Every web app development for agencies engagement includes these deliverables — scoped before we start, delivered before we invoice.
- Multi-tenant client portal with complete data isolation per client organization
- White-label theming: logo, brand colors, and domain configurable per client
- Client workspace with project tracking, file sharing, deliverable review, and approval workflows
- Client user management: invite contacts, assign roles, and control visibility per project
- Agency admin panel for client onboarding, workspace management, and billing oversight
- Project status updates with automated email notifications to client stakeholders
- Revision request system with tracked feedback cycles and approval sign-off
- File storage for deliverable uploads with version history and client access controls
- Billing integration for client subscription management and invoice generation
- Subdomain routing for per-client branded portals on your agency domain
Tech Stack We Use
Web app development for agencies uses the same core stack — Next.js 15, Supabase, TypeScript, Vercel — with multi-tenancy as the architectural priority. Supabase Row Level Security enforces client data isolation at the database level, so a misconfigured API route cannot expose one client's projects to another. White-label theming is stored in a tenant configuration table and applied at render time via CSS custom properties — changing a client's branding is a database update, not a code deployment. Vercel subdomain routing maps client-specific domains to the same Next.js application with tenant identification via the hostname. This architecture lets us onboard new clients to your portal in minutes rather than provisioning separate deployments.
Case Study
PLGOS — Multi-Tenant Platform Architecture
PLGOS is a product-led growth tool that serves multiple organizations from a single codebase with complete data isolation between tenants — the same architectural pattern that powers agency client portals. We built the multi-tenant foundation with Supabase Row Level Security, ensuring each organization's data is isolated at the database level rather than just the application level. The tenant management system allows new organizations to be onboarded in seconds. Admin users at PLGOS can view aggregated platform metrics without accessing individual tenant data. We shipped this architecture in 11 days and it has served 340+ tenants without a single cross-tenant data incident.
Read full case studyPricing Transparency
Web app development for agencies starts at $7,000 for a basic client portal with project tracking and file sharing. Full white-label platforms with multi-tenant architecture, subdomain routing, client billing, and workflow automation run $15,000–$40,000. If you intend to resell the tool to your clients with per-seat or per-client billing, we price the billing architecture as a separate scope item. All projects include full code ownership — you own the tool and can resell it without any royalty to Greta.
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
Can you build a white-label tool I can sell to my own clients?
Yes. We build white-label SaaS tools for agencies that want to offer proprietary platforms to their clients. The architecture supports per-tenant branding, feature flags, and usage metering. You manage the client relationships and pricing; the tool runs on your infrastructure. You own the code and the product — Greta has no ongoing claim on what you sell.
How do you ensure client data is isolated in a multi-tenant portal?
Isolation happens at the database level via Supabase Row Level Security policies. Every table has an RLS policy that restricts rows to the current user's tenant ID. A bug in the application layer cannot expose one client's data to another because the database itself enforces isolation. We test this isolation rigorously before every deployment.
Can each client have their own subdomain?
Yes. We configure Vercel's domain routing so client-a.youragency.com and client-b.youragency.com both serve the same Next.js application, with the hostname used to identify the tenant and load their branding. Adding a new client domain is a DNS configuration update — no code deployment required.
Can clients upload files and review deliverables in the portal?
Yes. We build file upload and review systems using Supabase Storage with signed URLs for secure access. Clients can upload briefs and assets; your team uploads deliverables; clients leave comments, request revisions, and mark work approved. Approval events trigger email notifications to both sides.
Can I manage billing for each client through the portal?
Yes. We integrate Stripe Billing so client subscriptions are managed within the portal admin. You can see each client's plan, payment status, and billing history. Clients can update their payment method through a Stripe-hosted billing portal. You receive payouts directly to your bank account via Stripe.
How do you handle onboarding new clients to the portal?
Agency admins create a new client workspace via the admin panel: enter the client name, brand colors, logo, and invite the primary client contact. The system provisions their workspace and sends an invitation email with a magic link. Onboarding a new client takes under two minutes from the admin panel.
Can the portal integrate with our project management tools?
We can build webhooks that sync project status between the client portal and your internal project management tool — Asana, Linear, Notion, or others — via their APIs. The direction of the sync is defined during scoping based on where your team primarily manages work.
How long does it take to build a client portal for an agency?
A basic client portal with project tracking, file sharing, and client user management takes 1–2 weeks. Full white-label platforms with multi-tenant branding, Stripe billing, subdomain routing, and workflow automation take 3–5 weeks. We scope and agree on timeline before starting.
Ready to ship?
Ready to build your agency's web app?
Start Your ProjectOr reach us directly at hello@greta.agency
Written by the Greta Agency team · Last updated April 2025