Deneb: Line Chart Tooltips that don't require you to hover directly over line

Hey Anonymous, you can layer a series of points with an opacity of zero spanning the entire x-axis and encode your tooltips off of those points. You'll want to set nearest to true.

Alternatively if you want a vertical line to show, you could do something similar with a series of rule marks and only have the one that aligns with your cursor be visible.

check out this example: https://vega.github.io/vega-lite/examples/interactive_multi_line_pivot_tooltip.html

if you still need additional help, I can try to generate an example spec later this evening when I have time.

Here you go Anonymous

If this is enough to get you going please consider liking this reply and choosing it as the solution.
gist
spec:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "params": [{"name": "dt", "expr": "hover['date']"}],
  "width": 800,
  "height": 400,
  "description": "Google's stock price over time.",
  "data": {"url": "data/stocks.csv"},
  "transform": [{"filter": "datum.symbol==='GOOG'"}],
  "layer": [
    {
      "encoding": {"x": {"field": "date", "type": "temporal"}},
      "layer": [
        {
          "mark": "line",
          "encoding": {"y": {"field": "price", "type": "quantitative"}}
        },
        {
          "params": [
            {
              "name": "hover",
              "select": {
                "type": "point",
                "fields": ["date"],
                "nearest": true,
                "on": "mouseover",
                "clear": "mouseout"
              }
            }
          ],
          "mark": {"type": "rule", "y": 0, "y2": {"expr": "height"}},
          "transform": [{"calculate": "format(datum['price'], '$')", "as": "price"}],
          "encoding": {
            "opacity": {
              "condition": {
                "test": "+hover['date'] === datum['date']",
                "value": 0.5
              },
              "value": 0
            },
            "tooltip": [
              {"title": "Symbol", "field": "GOOG"},
              {"title": "Price", "field": "price"}
            ]
          }
        }
      ]
    }
  ],
  "config": {"axis": {"grid": false}}
}