Dev & Preview

The CLI can run scripts and flows against a remote workspace without deploying them, which is useful for iterating on local files, validating codebase scripts, or testing flow changes with local inline script modifications.

wmill script preview

Preview a local script file against the remote workspace. Supports both regular scripts and codebase scripts (which are bundled before running).

wmill script preview <path> [options]

Options

Option	Description
-d, --data <data>	Inputs as a JSON string, @filename, or @- for stdin.
-s, --silent	Only output the final result (no logs, useful for scripting).

Examples

# Regular script
wmill script preview u/admin/my_script.ts --data '{"x": 5}'

# Codebase script (bundled before preview)
wmill script preview f/codebase_test/my_script.ts --data '{"x": 7}'

# Silent mode for piping
wmill script preview f/scripts/hello.ts -d '{"n":3}' --silent | jq

wmill flow preview

Preview a local flow against the remote workspace. The flow definition is read from the local .flow / __flow folder — any changes to inline scripts are picked up without deploying.

wmill flow preview <path> [options]

Options

Same -d, --data and -s, --silent options as script preview.

Example

wmill flow preview f/my_flows/etl__flow --data '{"date":"2026-01-01"}'

wmill flow dev

wmill flow dev starts a local dev loop for a flow: it watches the flow's local files, and on each change pushes the flow so you can test it interactively from the Windmill UI with fast feedback.

wmill flow dev <path>

Run wmill flow dev --help to see the full set of flags. Use this when iterating on flow YAML / inline scripts and testing via the UI; use wmill flow preview when you want a one-shot run with a specific payload.