It looks like this also affects the text encoding, which makes the issue easier to see (open in editor):

{
  "data": {"values": [{"date": "2021-01-01"}]},
  "mark": "text",
  "encoding": {
    "text": {"field": "date", "timeUnit": "utcyearmonthdatehours"},
    "x": {"field": "date", "timeUnit": "utcyearmonthdatehours"}
  }
}

I am experiencing the same problem here. It is a pretty big issue for us and is blocking on going to production since data integrity is very important

Ahh, the joy of time zones again.

@rnvarma can you look into what's going on in the Vega specs? It would help us immensely scope the effort for the fix.

the config for the x encoding above is:

{
  field: "created",
  title: "Created",
  type: "temporal",
  timeUnit: "utcyearmonthdate",
  axis: { format: "%b %d" },
}

The date value itself in the data is 2020-08-04T00:00:00. It is correctly using UTC for the x axis value, but in the tooltip converting to local time and going back to the previous day

I'm also running into this for point charts. Apologies if this isn't a minimal example, I'm new to Vega-Lite.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {
    "values": [
      {"Date": "2020-01-01", "Value": 10}
    ]
  },
  "mark": {"type": "point", "tooltip": true, "point": true},
  "height": "container",
  "width": "container",
  "encoding": {
    "x": {"field": "Date", "type": "temporal"},
    "y": {"field": "Value", "type": "quantitative"},
    "opacity": {"condition": {"param": "hover", "value": 1}, "value": 0.1},
  },
  "title": {"text": "Diff"},
  "params": [
    {
      "name": "hover",
      "bind": "legend",
      "select": {"type": "point", "fields": ["symbol"]}
    }
  ]
}

Open the Chart in the Vega Editor

@jakevdp Do you plan to upgrade the altair version so it supports scale on the tooltip?

Still running into this issue. Any ETA for a fix?

I haven't had cycles to look into this yet. Can you investigate and maybe send a pull request?

I can take a look. I had thought the workaround wasn't working, but it actually does. The schema has a squiggle under the value, but I am learning that shouldn't always be trusted.

Anyone find a solution for this issue yet? I was going crazy thinking there was an issue with my data or how my data was read by altair, but finally realized it's an error in how altair renders the mark line tooltip.

You can add "scale": { "type": "utc" } to the encoding as a workaround.

My PR fixes the issue but I wasn't able to get it merged because of the github access token. It still might be worth trying to merge that, @domoritz

That worked - thank you!

You can add "scale": { "type": "utc" } to the encoding as a workaround.

My PR fixes the issue but I wasn't able to get it merged because of the github access token. It still might be worth trying to merge that, @domoritz

Did that PR make it in? If so, what version fixes this?