A data-driven A/B testing platform for YouTube creators to optimize thumbnails and titles for maximum CTR.
Overview
ThumbnailTest helps YouTube creators run real A/B experiments on their thumbnails and titles. I joined as a junior working alongside an experienced lead, learned the codebase and YouTube API intricacies, then eventually became the sole developer responsible for the entire frontend and new feature development.
The Problem
New users dropped off before running their first test — A/B testing felt intimidating and complex.
The Solution
Designed an onboarding flow with interactive demo showing that running a test only takes 5 steps. Made the process feel approachable. Was part of the team that scaled the product from $15K to $25K MRR.
Key Achievements
- 1Grew from junior to lead developer, taking full ownership of frontend and feature development
- 2Part of scaling the product from $15K MRR to $25K MRR
- 3Designed onboarding flow with interactive demo — improved user retention
- 4Reverse-engineered competitors to improve AI title generation and propose new features
- 5Built RAG chatbot backend: Hono/Bun service → YouTube API → transcript processing → Pinecone embeddings
- 6Ported Chrome extension to Firefox & Safari, navigating platform-specific API quirks
Technical Highlights
YouTube API & Extension Architecture
Maintained a Chrome extension that scrapes YouTube by replicating internal API request patterns. Not a simple REST integration — required understanding YouTube's undocumented request structures and keeping up with changes.
RAG Pipeline Architecture
Built end-to-end: Hono/Bun backend receives channel ID → fetches last 20 videos via YouTube API → extracts and cleans transcripts → generates embeddings → stores in Pinecone. Includes rate limiting and resource monitoring.
Cross-Browser Extension Porting
Adapted Chrome extension to Firefox (Manifest V2/V3 differences) and Safari (Xcode packaging, native container app). Each platform had its own gotchas around permissions and API compatibility.
Reflection
This was my first major project, and it taught me that the hard problems aren't always the obvious ones. The YouTube API scraping taught me more about reverse engineering and API patterns than any tutorial could. Going from 'the new dev' to 'the person who owns this' was the real growth.
Tech Stack
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