Leadbay: an AI-powered B2B prospecting platform

I built Leadbay's whole frontend from scratch in React: the web app sales teams use to discover leads, and its iOS and Android app. One codebase served the web and both mobile platforms, and kept pace with a product that changed at every iteration.

Client: Leadbay (Y Combinator F25)
Role: Senior frontend developer, React
Duration: 21 months, September 2023 to May 2025
Setting: Freelance, fully remote, full technical autonomy

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001·Context

Lead discovery for B2B sales teams

Leadbay is an AI-powered B2B prospecting startup. On its platform, sales teams browse leads by sector, location and size, follow their activity on a dashboard and find their leads on a map from their phone.

“I strongly recommend working with JB. He was instrumental in getting our frontend off the ground, handling everything with zeal, unwavering dedication, and unparalleled reliability.”

Milan StankovicCo-founder & CTO, Leadbay (Y Combinator F25)February 2025

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002·Approach

How I worked for Leadbay

Brief and my role: No existing code to start from: I owned the frontend throughout, working directly with the CTO and the product team.
Constraints: One codebase for the web, iOS and Android, and a product that changed with every iteration.
Technical decisions: A Redux state architecture for the whole app, Ionic for iOS and Android on the shared codebase, and a landing page in Framer and Spline 3D.
Checks and releases: I tested the application end to end with Cypress and integrated it fully into CI/CD.

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003·Deliverables

What I delivered for Leadbay

Web applicationThe platform's complete frontend in React and TypeScript, with Redux for state
Hybrid mobile appiOS and Android with Ionic, on the web app's codebase
Landing pageAn interactive landing page built with Framer and Spline 3D
Product iterationsFixes and new features shipped continuously as the product evolved