Sentry, a startup co-founded by a former Dropbox engineer that helps developers run more reliable code, just raised $40 million

• On Tuesday, the software monitoring startup Sentry announced it raised $40 million from Accel and New Enterprise Associates.
• CEO and co-founder David Cramer started Sentry as an open source project while he was still an engineer at Dropbox.
• Cramer tells Business Insider that in Sentry's earliest days, not all investors understood why open source software was important.
• Cramer says making its software available as open source has allowed it to spread faster among developers.
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When Sentry CEO and co-founder David Cramer first started creating his error monitoring software, he felt like it was "two full time jobs."

At the time, he worked as a software engineer at Dropbox, while Sentry was a side project that he worked on in his spare time. Sentry, which helps developers understand and mitigate the impacts of bugs and other problems with their code, was released as open source - meaning it was free for anyone to use, download, or modify. It caught on with the open source community, leading Sentry to a prominent place among developers. Now, on Tuesday, Sentry announced it raised $40 million in series C funding led by Accel, with participation from existing investor New Enterprise Associates. Including this investment, Sentry has raised about $107 million all told.

"People will hear about Sentry and learn about the numbers and say, 'I had no idea Sentry was that big,'" Cramer told Business Insider. "We want to be explaining more of what the value is for these organizations that are trying to go to this modern emerging tech."

While Sentry's core software is free, Sentry sells a cloud-hosted service that's easier for developers to use, rather than having to run it on their own servers.

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"The way we always think about is you as a customer is, you want to call an Uber to get home. You want to load the app on the phone. If the app crashes, what do you do?" Cramer said. "For me personally, I would probably open Lyft. What we do is we give the right information for those kind of events to the right time."

A 'big change in how software development works'

Cramer left Dropbox in 2015 to start Sentry. Initially, he says, not all investors understood the value of open source and it was difficult to explain to investors why it mattered. Accel and NEA, who both invested in the round announced today, were two of the earliest believers, Cramer says - they both invested in Sentry's Series A round. "Do you go with an interesting product you didn't build yourself or one that clearly has something for you?" Cramer said. "It was interesting back in the day. Four years ago open source was still a little foreign. Good investors already identified there was something here. This is where Accel and NEA continue to be really bullish...Once we were able to secure that first investment, it was a lot easier."

Still, Cramer says that when he first started Sentry, he didn't realize how big the product would become. But he says it has become popular because of its focus on developers, which allows them to update their code faster and more often.

Read more: VCs say these 19 startups for open-source software developers will blow up in 2019

"When we started with Sentry, it was very much catering to the problems we had at the time," Cramer said. "Over the course of time, we saw this big change in how software development works...It's about, how can you more quickly make changes to the business? That often also increases the risk and the likely chance of these issues. With something like Sentry, it helps you identify those in real time and decide what you want to do immediately."