December 2025 (2025-12) focused on strengthening code quality in biomejs/biome. Key feature delivered was the introduction of a noMultiAssign lint rule to prevent chained assignments, ported from ESLint (#8316). This change enhances readability and reduces risk of subtle bugs in complex code paths. The work included a single, targeted feature with a commit that ported the rule: d64e92d485e9f19ac77c4e00e2f3d6366079dadd, co-authored by Maikel van Dort. No major bugs were fixed this month; the priority was proactive quality improvements. Overall, the initiative improved code safety, consistency, and maintainability, and sets the stage for broader lint policy adoption across the repository. Technologies demonstrated included ESLint-based lint rule porting, JavaScript/TypeScript linting, and collaborative development practices with cross-team contributions.