Relja Bulajić · Founder · Full-Stack & AI Engineer · Belgrade
I engineer AI products, end to end.
12 of my own apps live on the App Store with 4,000+ users, and clients get the same founder-level ownership: production AI, custom Python backends and polished native front ends.
Selected work
All projects →
AI Engineering
Production AI, engineered, not just prompted.
I ship AI as real product infrastructure: multi-model systems, agent pipelines, vision, voice and generative image features, all grounded in real user data and tuned for reliability, latency and cost.
Multi-model orchestration
Load-balancing across Claude, GPT and Gemini with cost-tiered routing: 4o for depth, 4o-mini for scale.
Agent pipelines
Background research and reasoning agents running on a custom FastAPI backend, not a single prompt.
Generative & image AI
AI image generation and photorealistic virtual try-on: creating new imagery, not just reading it.
Vision pipelines
Photo-to-structured-data: garment, food and skin analysis, plus on-device Vision OCR.
Voice & language
On-device transcription, natural-language intent parsing and AI-graded spoken answers.
On-device & private AI
Apple Vision, Speech and Core ML models running on-device, with edge proxies that never store user photos.
Grounded, guardrailed reasoning
Coaching and scoring grounded in each user's own data, backed by deterministic validation rules.
Latency & cost engineering
Sub-three-second voice pipelines and cost-tiered model routing: AI budgeted like production infrastructure.
The stack
Full-stack by necessity, iOS-obsessed by choice, every tool here is proven in shipped products.
Full-stack, for real
A graduated software engineer who owns the whole system.
I hold an engineering degree in software and run my own portfolio of startups, and it shows in how I build: the SwiftUI interface, the Python or Firebase backend behind it, the database schema, the payment rails and the deployment pipeline, all designed by one person who understands every layer and has skin in the game. No hand-offs, no gaps where bugs hide.
Security-first
Zero security incidents. Ever.
Every app I ship is hardened before launch: audited auth flows, strict Firestore and row-level security rules, App Check, encrypted storage via CryptoKit and Keychain, and secrets that never touch git. Backed by hands-on DevOps and server administration, so the infrastructure is as solid as the code.
- Security audits on every release
- Hardened auth, rules & App Check
- Secrets hygiene & encrypted storage
- DevOps, deployment & monitoring
Straight from Xcode
The same view, twice: the SwiftUI that ships, and what your users see.
1import SwiftUI2import CoreMotion34struct PostureView: View {5 @State private var pitch: Double = 06 private let motion = CMHeadphoneMotionManager()78 var body: some View {9 VStack(spacing: 24) {10 PostureRing(angle: pitch)11 Text(pitch < 12 ? "Aligned" : "Slouching")12 .font(.title2.weight(.semibold))13 Button("Recalibrate") { recalibrate() }14 }15 .onAppear { startTracking() } // AirPods sensors16 }17}
What clients say
“Relja is transparent, honest, and truly proactive. He doesn't just execute tasks, he thinks ahead and brings great ideas to the table.”
“The handover was fast, clean, and professional. He communicated clearly and delivered exactly what was promised.”
“Relja is a great professional. He communicated well along the way and helped me a lot to resolve the issue I was facing.”
Built to ship.
When I'm not building for clients, I'm building my own startups. Every project gets that same founder energy: design, code, App Store, owned end to end.