rightmodeler is a CLI tool that replays existing agent traces through cheaper candidate models and measures their outputs against previously accepted results. It autodetects ten trace formats from platforms like LangSmith, OpenAI SDK, Langfuse, and Braintrust into a unified per-step schema. Each candidate model is evaluated for output agreement, cost savings, evidence quality, and abstentions. Approved model swaps are packaged and shipped as pull requests with evidence attached, turning model migrations into a standard code review workflow.