Altair — Calendar Heatmap

GitHub-style 365-day grid: weeks across, days of the week down. Colour interpolates from surface to accent based on activity. Hover any cell for the exact date.

Notes

• Each cell is a Vega-Lite rect with x = week, y = weekday. The colour scale is a two-stop linear interpolation, which renders as a continuous palette rather than the 5-step discrete one we used in the Plot version.
• Tooltips show ISO-date, weekday name, and activity count — all from declarative encoding.tooltip entries.
• Vega-Lite’s legend renders an automatic colour gradient. We kept the title short (Activity) and pinned gradientLength to keep it compact.
• Pseudo-random data is generated once at module scope with a deterministic seed so SSR and client agree on cell values.