For Early‑Stage Startups

Full‑stack developer for early‑stage startups — APIs, backend systems & mobile apps

Most founders need one reliable developer who can handle everything. I build it so you don't have to coordinate a team to ship.

Book a free 20‑min call
Sergio Pereyra
React Native
Next.js
Supabase
TypeScript
PostGIS
Flask
MySQL
AI APIs
SaaS Architecture
Shopify
Tailwind CSS
PostgreSQL
React Native
Next.js
Supabase
TypeScript
PostGIS
Flask
MySQL
AI APIs
SaaS Architecture
Shopify
Tailwind CSS
PostgreSQL
What I Build

Services that ship fast, scale safely.

🔌
APIs & backend systems
Scalable APIs, database design, and server architecture using Python/FastAPI/Django
📱
Mobile & web apps
Full product builds with React and Node — from wireframe to deployed app
🔧
Legacy fixes & audits
Inherited a messy codebase? I clean it up and make it scale
Case Studies

What I've built for founders.

⛓️
NextBlock — Blockchain API
$250K
Revenue in 60 days
$0
Starting point
60
Days to results
Problem
The founders needed a high-volume blockchain API that could handle transaction spikes without downtime — while coordinating a distributed team with no clear architecture in place.
What I Built
I designed and built the full backend from scratch — database schema, API layer, and a React frontend — using Python/Flask and MySQL. The system was built to scale horizontally so transaction volume was never a ceiling.
Result
$0 → $250,000 revenue in 60 days.
PythonFlaskMySQLReact
🌍
GTA GeoGuesser — Viral Web App
50K+
Users
Viral
Organic growth
Fast
Load performance
Problem
The challenge wasn't just building a fun game — it was building one that could survive going viral. 50,000+ users hitting the app at once will expose every performance shortcut taken during development.
What I Built
I built the full product — Django backend, Tailwind frontend — with performance and shareability baked in from day one. Every page load was optimized, and the sharing mechanics were designed to drive organic loops.
Result
50,000+ users through organic sharing alone, zero infrastructure failures under load.
DjangoTailwindSQLite
📱
beepr — Native Mobile Migration
0
Downtime during migration
100%
Geolocation reliability
51
Edge functions audited
Problem
The team had a working Capacitor WebView MVP — but it wasn't production-grade. Real-time features were unreliable, background geolocation was inconsistent, and the codebase needed a full audit before scaling.
What I Built
I migrated the entire app to React Native, audited all 51 Supabase Edge Functions, implemented PostGIS for geospatial engineering, and rebuilt the background geolocation system from the ground up.
Result
Zero downtime during migration, 100% background geolocation reliability in production.
React NativeSupabasePostGIS
Tech Stack

Tools I ship with.

Python Django FastAPI Node.js React React Native PostgreSQL REST APIs Docker
Career

Work Experience

Mar 2026 - Present
React Native Engineer
The Galindo Consulting Group · beepr
Leading the full native migration of beepr from a Capacitor WebView prototype to a production-grade React Native (Expo Bare) app. Audited 51 Supabase Edge Functions, implemented PostGIS geospatial engineering, designed Travel Mode, and achieved zero-downtime migration with 100% background geolocation reliability.
React NativeExpoSupabasePostGISTypeScript
2023 - Present
Full Stack SaaS Developer
Freelance / Independent
Building and shipping AI-powered SaaS products that generate revenue fast. Delivered NextBlock ($250K in 60 days), GTA GeoGuesser (50K+ users), Interviewiz, and a Calendly-style scheduling platform. Clean architecture, usage-based billing, and payment integrations from day one.
Next.jsFlaskAI APIsMySQLStripe
2021 - Present
E-Commerce & SEO Specialist
Multiple Clients
Designed and developed Shopify stores, WordPress sites, and local SEO lead-gen platforms for clients across cannabis, food & beverage, health, and home services industries. Full ownership of design, branding, SEO, and performance optimization.
ShopifyWordPressSEOBranding

Working on something that needs a solid backend or a full product built? Let's talk.

Book a free 20‑min call
Let's Work Together

Start a Project

I build MVPs in 4-6 weeks with clean architecture, payments, auth, and scalability included from day one. Let's talk about your idea.

📧 Emailsperey@gcgiglobal.com ⌥ GitHubgithub.com/sergiop99 💼 LinkedIn/in/sergiopereyradev