Browser-harness drives a browser at the coordinate/CDP level instead of having the agent generate fresh Playwright scripts on every run. The token win is structural: you preconfigure how to navigate your site once, and the agent reuses that structure rather than re-producing the nav code (and re-burning tokens) each time.

It sits between raw Playwright, which throws its generated scripts away every run, and Stagehand, which caches the resolved action outright. If your agent runs the same browser flows repeatedly, that preconfigured structure is what stops the bill climbing. The browser-work angle on Token Saving.