Software Engineer, Platform

Sim•San Francisco, CA

3h•Onsite

About The Position

Sim is a YC X25 company, backed by a $7M Series A led by Standard Capital with participation from Paul Graham, Perplexity, SV Angel, and Y Combinator. Based in San Francisco, the company's mission is to enable agents to run the world, with Sim being the primary means for this. The role involves leading the Sim platform, which is a visual, end-to-end agent builder used by tens of thousands of developers. The platform is described as the "Figma for AI agents," allowing developers to connect LLMs, tools, APIs, and logic blocks into complex agentic workflows through an intuitive drag-and-drop canvas. The goal is to make this experience fast, delightful, and powerful, eliminating the need for developers to write agents in code. This is a foundational role where the engineer will define the front-end architecture, set performance standards, and shape the developer ergonomics of a product used by over 70,000 builders. As part of a small team, the engineer will own the entire surface area that developers interact with.

Requirements

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

Nice To Haves

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

Responsibilities

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