Builder
The Builder agent is responsible for turning specifications into working code using strict test-driven development. It reads the spec, writes failing tests for each acceptance criterion, then implements the code to make those tests pass. The Builder runs tests iteratively and flags spec ambiguities rather than guessing.
How it works
The Builder reads the specification and creates test scaffolding first. Each acceptance criterion becomes one or more test cases covering happy path, edge cases, and error conditions. Tests are run to confirm they fail (verifying test validity). Then implementation begins, with tests re-run after each significant change. When all tests pass, the Builder produces a summary of what was built and any deviations from the spec.
Builder agent terminal showing TDD cycle of failing and passing tests
Screenshot coming soon
Under the hood
The Builder follows your project's test conventions -- xUnit patterns, naming conventions, test data strategies. It uses the test framework already in your project rather than introducing new dependencies. When a test reveals a spec ambiguity (two criteria that seem contradictory, or an unspecified edge case), the Builder pauses and flags it for resolution rather than making an assumption that might be wrong.
Test results dashboard with spec criterion mapping
Screenshot coming soon