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Baseline Widget: Definition, Implementation, and Expansion on MDN

8 March 2026 by
Suraj Barman

Baseline Widget Overview

The Baseline widget is a visual indicator added to MDN reference pages that instantly conveys a feature's support status across major browsers. By applying a clear three‑tier model-Limited availability, Newly available, and Widely available-it helps developers assess readiness without consulting raw data, streamlining feature adoption decisions.

Deep Technical Analysis

Implementation of the widget relies on the web platform support data curated by the Web Features project. The system evaluates each feature against a core browser set, now expanded to include mobile versions, and assigns a status based on recent releases. When a feature meets the newly available criteria, the widget displays additional metadata such as the exact release date and a concise description, enabling developers to track the progression from debut to widespread stability.

Widget Status Categories

Three distinct categories are presented:

  • Limited availability: Feature support is sparse or experimental.
  • Newly available: Feature has just reached all stable core browsers the widget shows the rollout date (e.g., CSS custom properties on April 5 2017).
  • Widely available: Feature has been stable for at least 30 months, indicating broad user adoption.

Baseline Timeline Mechanics

The timeline tracks two primary events per feature: the initial newly available release and the subsequent transition to widely available after a maturation period. This dual‑event model reflects real‑world adoption lag, accounting for user update cycles and operating‑system constraints.

Governance and Override Procedures

The Web Features governance team can manually adjust a feature's status to address implementation bugs or misleading data, ensuring the widget reflects practical usability rather than strict metric compliance.

Rollout Strategy and Coverage Expansion

Following a phased deployment, the widget now appears on 315 MDN pages, with plans to extend coverage as the Web Features dataset grows. Continuous feedback loops via the widgets icon allow the community to suggest improvements, maintaining alignment with evolving browser landscapes.