# Build a tool
A Lolly tool is a small folder of data. `tool.json` lists what people can change. `template.html` draws the result. A `hooks.js` file is added only when the picture needs a calculation the template cannot do.
From that folder Lolly builds the sidebar, draws the canvas and offers the export formats you allow. The same folder runs unchanged in the web app, the desktop apps and the command line, because each of them reads the folder through one engine.
You do not need code to make a tool. If you already have a finished design, [Share with rules](/info/create/create-a-tool.html) turns a Design document into a tool when you choose the parts people may edit. Those tools are ordinary tool folders too, compiled for you and run by the strict sideload runtime; [Design tool contract](/info/build/design-tool-contract.html) covers how.
This guide is for writing the folder yourself. Start with the two-file tool below, then use the reference pages for each part.
## Your first tool
A working tool needs two files. This one makes a social card with a heading and a background colour.
::: cols
## tool.json
```json
{
"id": "hello-card",
"name": "Hello card",
"version": "1.0.0",
"engineVersion": "^1.0.0",
"status": "community",
"render": {
"width": 1200, "height": 630,
"formats": ["svg", "png", "pdf"]
},
"inputs": [
{ "id": "heading", "type": "text",
"label": "Heading", "default": "Hello" },
{ "id": "background", "type": "color",
"label": "Background", "default": "#2a1a5e" }
]
}
```
## template.html
```html
```
:::
Each declared input becomes a control in the sidebar, a URL parameter and a CLI flag, all with the same `id`. The template prints the current values into `{{heading}}` and `{{background}}`, escaped for you. The seven top-level fields in `tool.json` are the ones the schema requires; [Tool manifests](/info/build/tool-manifest.html) covers the rest.
The hello card rendered with `--heading="Hello, Lolly"`: one rectangle in the background colour and one line of text.
Try the folder in one of two ways:
::: timeline
- **On any Lolly, with no clone.** Zip the folder and drop the zip on [lolly.tools](https://lolly.tools) or another Lolly. Choose **Install this tool** and accept the trust prompt; the tool opens on that device. Drop an edited zip again to replace your copy. [Try it without the monorepo](/info/build/tool-publishing.html#try-it-without-the-monorepo) has the details.
- **In a clone, from the terminal.** Put the folder at `community/hello-card/` and run `pnpm run cli hello-card --heading="Hello, Lolly" --output=hello.svg`. Run `pnpm run cli hello-card` alone to list its inputs.
:::
The template's root is an `