The implementation agent that writes your actual codebase
What does the Fullstack Builder do?
“Code belongs to the Develop sub-agent.”From the agent's actual system prompt
The Fullstack Builder is the implementation agent: a full coding agent running headless inside your project's live sandbox, editing files and running commands directly against a pre-installed Next.js project. In the Design stage it appears as the Frontend Engineer; in Develop it builds the whole stack.
It consumes the design system tokens and the PRD, so the code it writes implements the product you specified, screen for screen, on the tokens your Design System Agent locked. The Orchestrator is forbidden from writing code itself: implementation belongs here.
What tools does the Fullstack Builder use?
Full sandbox toolsetReads, writes, and edits files and runs shell commands inside the project sandbox
delegate_to_develop_fixReceives targeted auto-fix runs generated from QA findings
dispatch_to_design_builderRuns live Next.js builds in the Design Builder tab during the Design stage
Put the Fullstack Builder
Every agent works from the same shared context. Describe your idea once and the whole team builds on it.