Software Engineer, Platform

We're a small team, YC X25, and backed by a $7M Series A led by Standard Capital with participation from Paul Graham, Perplexity, SV Angel, and Y Combinator. We're based in San Francisco and build in person every day.

Our mission is simple: agents will run the world, and Sim is the primary means by which that happens.

You'll lead the Sim platform: the visual, end-to-end agent builder that tens of thousands of developers use every day. You'll own the front-end architecture, the real-time canvas, and the systems that turn visual flows into reliable, production agents.

Sim has been called the "Figma for AI agents" — an intuitive drag-and-drop canvas where developers connect LLMs, tools, APIs, and logic blocks into complex agentic workflows. Your job is to make this experience fast, delightful, and powerful enough that developers never want to go back to writing agents in code.

This is a foundational role. You'll define the front-end architecture, set performance standards, and shape the developer ergonomics of a product used by 70,000+ builders. On a small team, you own the entire surface area that developers interact with.

• Own the Sim visual canvas — the real-time, drag-and-drop workflow editor at the heart of the product

• Architect and build the front-end systems that render, connect, and manage complex agent workflows

• Design the interaction model for how developers create, test, debug, and deploy agents visually

• Build the bridge between visual flows and the underlying execution engine — ensuring what you see is what runs

• Drive performance and responsiveness across the editor, even as workflows grow in complexity

• Shape developer ergonomics and UX patterns across the platform — block configuration, variable wiring, real-time feedback, deployment flows

• Work across the stack in our Next.js monorepo when needed, shipping to production daily

• Set front-end standards for the codebase — component architecture, state management, testing patterns

• Design-minded full-stack engineer with deep React and TypeScript experience

• Strong sense of product and UX — you care deeply about how things feel, not just how they work

• Experience building complex, interactive UIs — canvas editors, real-time collaborative tools, visual programming environments, or similarly demanding front-end systems

• Track record of shipping polished developer tools or creative tools to production

• Deep understanding of front-end performance — you know how to keep complex interfaces fast and responsive

• High agency and ownership — on a team this small, you define the roadmap as much as you execute it

• Comfort working across the stack in a Next.js monorepo; backend work is part of the job

• Experience with real-time systems (WebSockets, CRDTs, or similar) is a plus

• Experience with AWS infrastructure is a plus

• Contributions to open-source projects are a plus

• Foundational impact. You're not joining a team — you're building one. Every decision you make shapes the product and the company.

• Real users, real scale. 70,000+ developers use Sim today. Your work ships fast and matters immediately.

• World-class backers. Series A - Paul Graham, Perplexity, SV Angel, and Y Combinator believe in what we're building.

• Open source at the core. We've been open source from day one and we're proud of it. 26,000+ GitHub stars and growing.

• Competitive salary + meaningful equity. Early team, significant ownership.

• Full benefits. Comprehensive health insurance, relocation.

• Visa sponsorship available.

Sim is committed to creating an inclusive environment for all employees. We celebrate diversity and are committed to creating an inclusive environment for all team members. We do not discriminate on the basis of race, religion, color, national origin, gender, sexual orientation, age, marital status, veteran status, or disability status.