InvoicePro: Engineering a Brutalist Invoicing SaaS

Most invoicing tools are cluttered, slow, and visually uninspiring. With InvoicePro, I set out to build the opposite: a 'Brutalist' financial tool that prioritizes raw speed, high-contrast typography, and uncompromising security for modern freelancers.

/02 The Architecture: Next.js 15 & Supabase SSR

For a platform handling sensitive financial data, security wasn't an afterthought—it was the foundation. I utilized the latest @supabase/ssr package to manage server-side authentication. By implementing PKCE auth flows, I ensured that magic link tokens are exchanged securely on the server, preventing common client-side interception attacks.

/04 Database Integrity with Row Level Security (RLS)

In a multi-tenant SaaS, the biggest fear is data leakage. I engineered a strict PostgreSQL schema where Row Level Security (RLS) acts as a hardware-level bouncer. Even if a hacker obtains the public Anon Key, the database mathematically prevents them from querying any invoice that doesn't belong to their specific UUID. Performance is maintained through composite indexes on user_id and created_at fields.

“In Fintech, trust is the only currency that matters. If your database isn't locked down at the row level, you don't have a product—you have a liability.

/07 The Monetization Engine: Paystack Integration

To handle subscriptions, I integrated Paystack's API with a robust webhook architecture. The challenge was handling 'asynchronous success'—ensuring a user is upgraded to 'Pro' even if they close their browser before the redirect finishes. I built a secure Node.js webhook handler that verifies Paystack's HMAC signatures and uses a Service Role God-Mode key to upsert the user's tier in real-time.

/09 Brutalist Design System

Visually, the app follows a 'Neo-Brutalist' aesthetic. I utilized a restricted color palette (#F4F4F2 and #0F0F0F) combined with the Inter typeface. By removing all unnecessary shadows and blurs, the interface achieves a 'Lighthouse 100' performance score, making the invoice generation process feel instantaneous and professional.