143.dev
Why we built 143
Coding agents are very impressive in fresh repos, but we needed more in order to actually get them working well in our production systems across teams of engineers and non-engineers. That's why we built 143 and open sourced it.
By John, from Assembled
At Assembled, we wanted coding agents to help with real product work, not just demos and internal tools. Even heading into 2026, we were not seeing the velocity increase we expected. Other people seemed to be getting huge leverage from new repos. We were still losing time to setup, context, CI, review, and handoff.
We kept asking what we were doing wrong. After talking to a lot of other teams, the answer felt much clearer: this was a shared infrastructure problem, not just an individual prompting problem.
We started with a small tiger team. We cleaned up our instructions, invested more in CI/CD, built agent hooks, and made the agent environment less fragile. All of that helped, but it also made the bigger issue obvious: we needed a system that made this work shared by the team, not trapped inside one engineer's terminal.
That is why we built 143.dev. We were inspired by internal systems like Stripe Minions and Ramp Inspect, but those were not available to the public. We wanted to build something open source that other teams could use, adapt, and improve.
Vibe coding is not the right word for what we want. I care much more about productionalized coding. The point is not one-off apps. It is helping professional engineers move faster on important work, and giving domain experts and non-engineers a real path to write real code in production systems.
That last part matters a lot to me. 143 should not pretend a PM, designer, support leader, or operator suddenly becomes a senior engineer. But they should be able to turn product knowledge into a scoped code change, with shared context, previews, pull requests, CI, and review gates before anything ships.
A lot of today's tools make individual engineers faster, but they can make the team part harder. That makes sense; many were built by engineers for their own workflows. Running engineering teams made us notice that a lot of primitives were sitting at the wrong level.
Automations should be visible to the team, not hidden on one person's laptop. Teams should be able to swap out intelligence as coding agents and models improve. Usage should be legible by person, PR, issue, automation, and outcome, not just token count. Hooks should make it natural to start work from Sentry issues, Linear assignments, PR comments, or scheduled checks. And you should be able to set up a great environment once for everyone, with the same repos, credentials, tools, logs, docs, and product context available to the whole team.
Open source from day one
I owe a lot of my career to early open-source work on Ruby on Rails. That is where I learned software fundamentals from people like Aaron Patterson, Santiago Pastorino, Jose Valim, and Jeremy Doerr. Their PR reviews, their patience, and their willingness to design-pair with strangers on the internet shaped how I think about software.
I was just a college student, but the Rails core team did not care who I was. If a PR was good and well-intentioned, it was welcome. I started with tests and tiny refactors, learned more of the codebase, and eventually fixed Active Record bugs. That work helped me get my job at Stripe and became the launching pad for the rest of my career.
I want 143 to be available in that same spirit. I hope it helps other people and teams the way open source helped me.
I also wanted the hosted version to feel like the old days of developer tools, when pricing was simpler. For hosted 143, we are charging just for the containers you run. Bring whatever LLM provider or coding agent you prefer. We want you to help pay for the servers, not make your team pay our model markup.
The name comes from 1943, when the Lockheed Skunk Works team built the XP-80 Shooting Star in 143 days. It is a nod to small teams with enough ownership and infrastructure to move quickly.
I really hope you like it.
John