> ## Documentation Index
> Fetch the complete documentation index at: https://docs.evidence.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Tooltip Fields

> Add extra rows to a chart's hover tooltip with the tooltip_fields attribute.

`tooltip_fields` adds extra rows to a chart's hover tooltip without dropping to `custom_echart`. Each field is an aggregate (or `GROUP BY`–safe) SQL expression that Evidence appends to the chart's query and renders as an extra row under the primary value.

## Example

```liquid theme={null}
{% bar_chart
    data="orders"
    x="month"
    y="sum(total_sales)"
    y_fmt="usd"
    tooltip_fields=[
        { value="count(distinct order_id)" label="Orders" },
        { value="sum(total_sales) / nullif(count(distinct order_id), 0)" label="Avg order" fmt="usd" }
    ]
/%}
```

## Fields

| Field           | Required | Description                                                                                                                                                                                           |
| --------------- | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `value`         | Yes      | SQL expression to show in the tooltip, e.g. `"sum(share)"`. Must be an aggregate or a `GROUP BY`–safe column — it runs under the same `GROUP BY`, filters, and date range as the chart's primary `y`. |
| `label`         | No       | Text shown to the left of the value. Defaults to a title-cased version of the expression.                                                                                                             |
| `fmt`           | No       | [Format code](/core-concepts/value-formatting) applied to the value (e.g. `"usd"`, `"pct1"`, `"num0"`, or an Excel-style custom format). Defaults to `num`.                                           |
| `color_by_sign` | No       | Colour the value green when ≥ 0 and red when \< 0. Defaults to `false`.                                                                                                                               |
| `down_is_good`  | No       | Flip the sign colouring so negatives are green and positives red. Only applies when `color_by_sign=true`. Defaults to `false`.                                                                        |

## Syntax

This is **Markdoc, not JSON** — the separator rules differ:

* **Object properties are separated by spaces, not commas**: `{ value="sum(x)" label="X" fmt="usd" }`
* **Array elements are separated by commas**: `[{ … }, { … }]`
* Strings use double quotes; booleans are bare (`color_by_sign=true`).

<Warning>
  Do not put commas *between properties inside an object* — `{ value="x", label="y" }` will fail to parse. Commas belong only *between array elements*.
</Warning>

## Map layers

`point_layer` and `area_layer` take a simpler form — an array of column-name strings:

```liquid theme={null}
{% point_layer data="plants" lat="lat" long="long"
    tooltip_fields=["fuel_type", "capacity_mw", "emissions"]
/%}
```