Substack Explorer, by Build to Launch, is for writers who want to know who else writes in their niche and how big they are. Find newsletters in your niche and see subscriber counts and engagement. Benchmark your newsletter against the top ones in your space and track how they grow. Developers get API documentation for the Substack endpoints the app uses, and MCP access is available via waitlist. Jenny built it to find newsletters in specific niches for her own research, then used it to study 3,000 articles by top AI writers.
I wanted to know where my own newsletter stood in my niche. After I read a study of 75,000 Substack newsletters, I worked with my AI assistant to analyze 1,200 newsletters across three keywords that describe Build to Launch. I published what I found and offered to run the same analysis for the first 10 readers who left three keywords in a comment. Each of those 10 requests came from a niche totally different from mine, and more kept coming, so I built an MVP that lets anyone run the search themselves. I built it in early 2025 with Cursor, as a personal research tool that happened to be shareable. At first it felt perfect, with a smooth UI and working data fetching. Then I fed it large sets of data and it slowed to a crawl, and it took a system-level fix to make it hold up. I still use it to compare a niche before I decide what to study more closely, and I used it to study 3,000 articles by top AI writers.