AI step

AI fill

The ai_fill step asks the AI to determine the right value or the right field from the page context — a resilient fallback when a layout varies and a fixed selector would be brittle.

In a workflow, this is a step object with "type": "ai_fill". Steps run in order, and each step can read the outputs of the steps before it. See the full workflows reference for the 30+ step types.

Writ runs on your own accounts, with your own credentials and data, on sites you are authorized to use.

Fields

Field	Type	Description
`description` required	`string`	What to fill, in plain words.
`selector`	`selector`	Optional hint to scope the AI to a region.

Example

A single ai_fill step as it appears in a workflow's steps array:

{
  "type": "ai_fill",
  "config": { "description": "Enter the shipping city from the provided address" }
}

How it behaves

AI steps are metered by the tokens they use; recorded steps replay with no AI cost.
Prefer deterministic fill/type steps; use ai_fill only where the page genuinely varies.

Where it runs

The ai_fill step executes wherever the run executes. On your local or BYO agent there is no compute charge and the agent can reach intranet-only systems; on Writ cloud the run is metered by running time (~$0.12 per browser-hour, from your plan’s included usage wallet.

Related steps

fill: Set a field's value in one operation.
ai_fill_form: Let the AI complete a whole form from the available data.
ai_continue: Let the AI decide and take the next actions toward a goal.

What next

Workflows - the full step vocabulary and the workflow object.
Recorder - capture steps by clicking through a site.
Managed endpoints - turn the workflow into a REST endpoint, or an MCP tool.