A line chart shows the U.S. 30-year fixed-rate mortgage average from the St. Louis Fed, drawn with the vega-lite-api library. The visualization uses a time-encoded x-axis and a quantitative y-axis without a zero baseline to emphasize rate fluctuations. Data loads asynchronously via d3.csv from a Gist, and the chart renders to SVG with a custom config for larger axis labels and tooltips. Vega-Lite API registers Vega, Vega-Lite, and d3, while vega-tooltip provides interactive hover details for each date and rate value.