Two years ago, Casey Primozic was wrapping up his undergraduate years at Valparaiso University in Indiana. He was also building a website -- for fun. Little did he know it would grow into a Wall Street obsession.

Now in 2020, his college side project,, has seen site traffic explode as everyone from day traders to institutions flock there for a picture of what retail investors are buying. Primozic says there’s evidence hedge funds are scraping his data. The 23-year-old programmer can hardly keep up with an overflowing email inbox and is getting barraged with pitches from advertisers.

“I’ve never really had anything I built really pop off in popularity quite like this,” Primozic said by phone from Seattle, where he works as a software developer for an early-stage tech startup. “It’s been an experience, for sure.”

Built in three months, Primozic’s aggregator has become a force unto itself in the rally engulfing U.S. equities, holding a mirror to the buying and selling decisions of small-time stock jocks and, arguably, amplifying their impact. The site solves a problem that has long vexed Wall Street’s intelligence-gathering machine: figuring out what retail investors are doing in real time. It’s also sparked a raging debate over how much little-guy investors are driving the gains.

Robintrack isn’t affiliated with the Robinhood investing app, but uses information gleaned from it to show trends in positioning among the brokerage’s users. Every hour, Robintrack downloads popularity data for every stock from Robinhood via a public application programming interface, or API. To Primozic’s knowledge, no other brokerage provides this data publicly and directly -- making Robinhood users a proxy for all individual investors.

Robinhood displays stock ownership data publicly for informational purposes, according to a company spokesperson.

That data is at the center of efforts to judge the role of retail day traders in the epic stock rally since late March. At minimum, it’s evidence they have been on the right side of a lot of improbably good trades. Robintrack shows hundreds of thousands of accounts opening in everything from cruise lines and airlines to bankruptcy stocks, many of which have surged.

Anywhere between 20,000 and 50,000 unique users now visit Robintrack on an average day, according to Primozic. Before this year, a typical day would only see up to 4,000 visitors. In the seven days before Monday, the website attracted 167,000 unique users and 286,000 separate sessions. The spike began back in late April, as Robinhood users piled into the United States Oil Fund LP (USO) amid negative crude prices.

While sharing similarities with other sets of bespoke consumer data that has come to captivate quants globally, Robintrack’s ease-of-use has made for a broader impact. For the last few weeks, anyway, it’s created a kind of observation effect in markets, particularly at their speculative edge, where the sight of retail accounts ballooning in this or that small cap is taken as a signal by others that they should dive in as well.

There’s a “cult of Robinhood watchers developing,” according to Peter Tchir, head of macro strategy at Academy Securities. SocGen quant strategists led by Andrew Lapthorne wrote in a note Monday: “The number of ‘odd’ trades coupled with the availability of Robinhood data via, has increased the noise level.”

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