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Sangwoo Han

Replit Agent Builder


Organization: Replit
Time: 10.2025 - 2.2026
Project Team: Sangwoo Han (Product Designer), Amadeo Pellicce (Product Manager, Tech Lead), Nick Ondo (AI Engineer), Phil MacEachron (Frontend Engineer), Ajay Nayak (Product Engineer)



What is Replit Agent Builder?

Replit’s Agent Builder (Externally knows as Automation Stack) lets users build and run multi-step, production-ready workflows using natural language. Powered by the Replit Agent and Mastra AI, it translates intent into event-driven automations with triggers, logic, integrations, and scheduled execution—making complex process orchestration accessible without traditional coding.

Context

This initiative began as an experimental hack by an AI engineer to explore whether Replit Agent could generate and orchestrate agents using Mastra and Inngest. As adoption and internal excitement grew, it became clear that formalizing and productizing the concept could meaningfully expand Replit’s existing app stack, turning a proof of concept into a scalable automation layer within the platform.

My Roles

  • Owned and designed the end-to-end product experience
  • Shaped product vision and go-to-market strategy
  • Partnered with internal teams and external customers to validate high-impact use cases and drive leadership buy-in



Key Decisions

  • Formalized Agent + Mastra + Inngest into a reusable automation layer, not just agent chaining
  • Designed for event-driven, production-grade workflows (triggers, async execution, error handling)
  • Avoided deterministic module authoring — Replit is vibe-coding native, and modules are AI-generated
  • Reframed the flowchart as a debugging & transparency layer, not a primary builder
  • Added natural language descriptions at the agent and module level to preserve clarity without sacrificing simplicity



Impact

  • Successfully launched; 100K automations created within the first week
  • Elevated a single-engineer experiment into a platform-level automation capability
  • Expanded Replit beyond app generation into workflow orchestration
  • Established the foundation for Replit’s evolution from an app-building tool to a “build everything” platform
  • Drove internal alignment and leadership momentum toward long-term product expansion