# Preview

MUST use when opening the Windmill dev page / visual preview of a flow, script, or app.

- Repository: https://github.com/windmill-labs/windmill (18352 stars)
- Category: Writing
- License: see repository
- Last updated: 2026-11-01
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add windmill-labs/windmill --skill preview -g -a claude-code -y`
Codex: `npx skills add windmill-labs/windmill --skill preview -g -a codex -y`
Cursor: `npx skills add windmill-labs/windmill --skill preview -g -a cursor -y`
Gemini CLI: `npx skills add windmill-labs/windmill --skill preview -g -a gemini-cli -y`

## Description

MUST use when opening the Windmill dev page / visual preview of a flow, script, or app. Triggers on words like preview, open, navigate to, visualize, see the flow/app/script, and after writing a flow/script/app for visual verification.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Windmill Preview Workflow

Use this skill any time the user wants to **see**, **open**, **navigate to**, **visualize**, or **preview** a flow, script, or app, and any time you've just finished writing one and want to offer visual verification.

The Windmill dev page renders the flow graph / script editor, lets the user step through steps, and live-reloads on every save. It runs locally via `wmill dev` and is reached on a localhost port.

## Two independent decisions

### 1. Mode: proxy or direct?

`wmill dev` runs in two modes; pick by asking what kind of URL whatever will display the preview needs.

- **Proxy** (`--proxy-port <port>`), exposes the dev page on `http://localhost:<port>/`. Use it when the embedder you'll hand the URL to **only accepts localhost URLs** (most in-IDE / in-chat preview embedders do, because they sandbox cross-origin loads).
- **Direct** (default), the user's browser loads the dev page from the remote workspace's HTTPS URL; the local `wmill dev` only runs the WebSocket back-channel for live reload. Use it when the URL will be opened in a regular browser tab.

Default to **direct** unless you have a specific embedder that needs localhost.

### 2. Who starts the server?

- **You start it** in the background. Spawn `wmill dev …` (or `wmill app dev …`) yourself, capture the URL it prints, do whatever's next (open a tab, hand the URL to an embedder).
- **The runtime starts it from `.claude/launch.json`.** Some runtimes (currently the Claude Desktop / Claude Code MCP preview integration, tools prefixed with `mcp__Claude_Preview__`) can read a `launch.json` configuration and launch the dev server on demand when you invoke their preview tool. **Only take this path if you actually have such a tool**, otherwise nothing reads the file and `wmill dev` never starts.

The two decisions compose. The common cases:

The rest: https://github.com/windmill-labs/windmill/blob/HEAD/system_prompts/auto-generated/skills/preview/SKILL.md