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

> ## Agent Instructions
> Automate.ax automations are TypeScript programs.
> Use Bun for installation and command examples.
> Use Automate.ax for the product name and automate.ax for the package, CLI, and domain.
> Treat documented public APIs as current; do not invent transitional or deprecated names.

# Create Custom Field

> Create a typed Custom Field on a Trello board.

`trello.createCustomField` creates a Custom Field definition on one board.

The board must belong to a Standard, Premium, or Enterprise Workspace. Free Workspaces return Trello's `403 Custom Fields Power-Up disabled for board` response; see [Authorization and raw API](/reference/integrations/trello/authorization-and-raw-api#custom-fields-prerequisite).

```ts automations/create-trello-custom-field.automation.ts theme={null}
import { automation, onDashboardRun } from "automate.ax"
import { trello } from "automate.ax/trello"

export default automation("Create Trello Custom Field", () => {
  onDashboardRun({ title: "Create Trello Custom Field" })
  trello.createCustomField({
    board: "board-id",
    displayOnCardFront: true,
    name: "Estimate",
    position: "bottom",
    type: "number",
  })
})
```

Provide `board`, non-empty `name`, and `type` as `"checkbox"`, `"date"`, `"list"`, `"number"`, or `"text"`. `displayOnCardFront` defaults to `true`. `position` accepts `"top"`, `"bottom"`, or a nonnegative number and defaults to `"bottom"`. Optional second argument `{ account }` selects a Trello binding.

Returns the created `TrelloCustomField`. Add dropdown choices separately with `trello.createCustomFieldOption` when `type` is `"list"`.