Robinhood itself posts the number of account holders who hold any individual equity on that stock’s page, something that none of the other retail brokerages do. Primozic’s program simply aggregates that data into a broad snapshot.

“It’s accountable, they’re data from Robinhood -- there is no guessing going on,” Benn Eifert, managing partner of QVR Advisors, said of the Robintrack platform. “That’s a relatively unique thing about Robinhood relative to TD Ameritrade or Schwab or something, where most brokerages don’t provide that data. Robinhood just does.”

The traffic increase at Robintrack has been so large that Primozic has had to make a couple changes to the site’s operations to keep up with the overflow. Visitors to the site aren’t just perusing. Rather, many are pulling the available data into their own programs.

“These days, especially, there’s at least three or four people who will run these scrapers at any given time,” he said. “I’ve actually had to limit the rate at which they can do it just to prevent them from overloading my hardware.”

Primozic claims he’s seen evidence that users at hedge funds including D.E. Shaw & Co. and Point72 have looked into or are directly collecting data from Robintrack. Representatives of the firms declined to comment on whether they’re plugging into Robinhood.

“It’s certainly a thing,” said Larry Tabb, Bloomberg Intelligence’s head of market structure research. “We are seeing more of this through social investing, where folks either post their own trades or firms broadcast folks’ trades. This can be looked at in two ways, first as a self-fulling prophecy -- i.e. pump and dump. Or, it’s providing the market the same information that their execution partners have.”

Compliance representatives at large Wall Street banks have also contacted Primozic, he says, asking how he sources the data to figure out how they themselves can use it legally.

“To be clear, that’s totally fine with me. I allow the data I collect to be used freely for any purpose,” he wrote in an email. “It was neat to see that the institutional investors are interested in the data just the same as everyone on Twitter.”

There’s an ironic subplot to Primozic’s success with Robintrack. Shortly after releasing the website to the public back in May 2018, folks at Robinhood caught wind. A recruiter from the investing app reached out to Primozic, and the company flew him out to interview for a job.

He didn’t get it.