---
title: Variables
description: Define a value once in blume.config.ts and write {{name}} anywhere a page needs it, in prose, code, links, and component props.
---

Define a value once and use it across every page. A version number, an API host, or a product name lives in `blume.config.ts`, and `{{name}}` in a page reads its value:

```ts blume.config.ts lineNumbers
export default defineConfig({
  variables: {
    version: "2.1.0",
    "api-url": "https://api.example.com",
  },
});
```

```mdx docs/quickstart.mdx
Install version {{version}}, then call {{api-url}}.

## What's new in {{version}}

<Card title="Release {{version}}" href="{{api-url}}/changelog" />
```

References work in prose, headings, links, code blocks, inline code, and component props, in `.md` and `.mdx` pages and in the files they [include](/docs/content/includes). Spaces inside the braces are fine (`{{ version }}`). Change the value in the config and every page picks it up on the next build.

Names take letters, digits, `_`, and `-`. Values are plain text on one line.

## Where they apply

A variable is replaced before anything reads the page, so the rendered HTML, [search](/docs/configuration/search), the page's [`.md` mirror](/docs/discoverability/markdown), and `llms-full.txt` all show the value.

Front matter is left as written: a `title` or `description` with `{{version}}` in it shows the braces.

## Undefined names

A `{{name}}` that isn't defined in prose is a build error, `BLUME_UNDEFINED_VARIABLE`, reported at its line, so a typo never reaches readers. Inside a code block or inline code, an undefined name is left as written, since templating examples like a Handlebars `{{title}}` are common there.

To show a reference in prose without defining it, put it in inline code: `` `{{name}}` ``.

A site that defines no variables is unaffected: `{{…}}` in its pages stays as written.