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Stage ② of the loop · owned by the Builder skill.
Build takes a validated agentspec.yaml and implements it into the target you chose — a framework or a coding-agent harness. It works test-first: it lays down the checks the spec implies, then builds until they pass. Two agents run in tandem: an implementer writes the code, and a reviewer checks each pass against the spec and flags drift. They loop — implement, review, correct — until the checks are green. You get the finished agent and a build report, not the intermediate steps.

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Run it

Point Helix at the spec and the target:
Other ways people ask:
  • Implement the Lead Qualification agent for Codex — enrich each lead, score it, and route the hot ones to sales — and stop at a working agent I can run.
  • Add the escalation rule so the Refund Processing agent hands disputes over $500 to a human instead of auto-approving.
Build implements the spec, runs its checks, and stops when you have a working agent.

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Keeping spec and code in sync

Code drifts from the spec as you iterate. When that happens, ask Helix to resync the spec — it reconciles agentspec.yaml against what the implementation actually does, so the definition and the code stay in agreement. Any change to the spec is shown to you before it’s written.

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What you get

  • A working agent that implements your spec.
  • A spec and an implementation that agree.

Next: Evaluate

Score the agent against your real traces.