PartyKit implements real-time multiuser interaction for any application

If a company wants to offer in-app messaging or voice calls, they don’t need to develop the infrastructure themselves when they have something like Twilio at their disposal. Similarly, if payment support is required, there’s Stripe, and the mighty Google for geographic maps.

But what if a developer is tasked with building real-time multi-user collaboration like Google Docs or Figma into their software? That’s where things get a little more complicated. One option is to build the software yourself and deploy it in the cloud, but this is a complex and resource-intensive task. Another option is to use a managed service such as Pusher (currently owned by Twilio competitor MessageBird) or Atlassian-backed Liveblocks. These services are popular, but can hardly provide the flexibility a company needs when building its own software, as they are proprietary third-party services.

That’s where PartyKit comes in – a deployable, open source platform with all the libraries needed to integrate multi-user functionality into your applications.

“Previously, building and scaling collaborative backends required specialized expertise and large operational investments,” PartyKit founder and CEO Sunil Pai told TechCrunch. “With PartyKit, it’s literally a matter of minutes, and it’s accessible to most.”

Pai left his position as a senior systems engineer at Cloudflare last year and soon after launched the initial version of PartyKit in partnership with whiteboard collaboration app Tldraw. Over the intervening months, Pai completely reworked the initial product to make it suitable for a wider range of tasks and then raised $2.5 million in pre-funding.

That amount was led by venture capital fund Sequoia Capital, with participation from Cursor Capital, Remote First Capital and angels including Cloudflare co-founder and CEO Matthew Prince and Vercel co-founder and CEO Guillermo Rauch.

PartyKit is perhaps somewhat similar to Vercel or Netlify, but with a particular emphasis on collaboration – developers simply bring in all their code and then can integrate PartyKit with their own tools and services and test it on their local machines in continuous integration/continuous delivery (CI/CD) environments.

“By providing powerful low-level building blocks on which developers can write code, PartyKit allows developers to build applications on their own terms without worrying about the complexities of the underlying infrastructure,” added Pai.

In addition to facilitating real-time human collaboration, perhaps within a digital whiteboard, game or code editing application, companies can integrate large language models (LLMs) from OpenAI or even their own models so that a human operator can be paired with an AI agent and PartyKit handles all the long-running processes, memory and context storage for the machine agent. All with just a few lines of code.

“Building applications like this requires a real-time infrastructure that delivers data and actions to users,” Pai said. “LLM now means people are collaborating not just with humans, but with small AI entities with different goals. There is a huge shortage of platforms that can allow developers to build such applications. That’s why I created PartyKit.”

PartyKit’s platform is built on Cloudflare, indicating that the technology dates back to when Pai worked at that cloud infrastructure company for more than a year. And before that, Pai worked on multi-user applications at Meta*’s Oculus division (low latency and real-time are key to collaboration in VR).

“In each of these situations, I was surprised at how much investment and effort was put into the infrastructure to enable collaboration,” Pai said. “While the rest of the application stack has become very accessible to developers over the past 20 years – I remember a time when you had to be a database specialist to put a blog online – the same level of commercialization and accessibility hasn’t happened in multi-tenant infrastructure. It’s no coincidence that it takes a multi-billion dollar company to create a Google Docs, Figma, or a triple-A game.”

PartyKit has been in open beta testing since July, and a few weeks ago the company announced that it was hiring its first employees. So today, the company actually announced the funding and launch of its platform. The company is also gearing up to roll out premium enterprise-focused features and services, including team support, analytics, compliance, and more. Pai also confirmed that PartyKit will support both on-premises and cloud hosting for those who need it, which is especially important for enterprises that face strict regulatory scrutiny over the storage and handling of sensitive data.

“The idea is to make real-time multiplayer development available to millions of developers around the world, and the only way to do that is to sell it as infrastructure,” Pai said.