# change_subdomain

Source: https://modulify.ai/docs/mcp/sites/change-subdomain

Changes the free modulify.website address a site is served on, and the old address stops working at once.

- Title: Change the free web address
- Scope: `sites:write`
- Access: Destructive

This is the live public web address, so the old one stops resolving the moment this succeeds, and every link, bookmark or QR code pointing at it breaks. The tool tells the client to do this only when you have asked for this exact address. Custom domains, if the site has any, are not affected.

The CDN address of the site moves with the subdomain too. A published site, with custom domains or not, must be published again for its storage files, email sending and analytics API calls to keep working. Files linked by their full CDN address in pages or stored content, such as a public file embedded in a page, must be updated to the new address, because a publish alone does not change them.

The value is 3 to 63 characters of lowercase letters, numbers and single hyphens, never at either end, and it is lowercased for you. Reserved words and anything starting with `prj-` are refused. If another site anywhere on the platform already holds it, the call fails with `That subdomain is already taken!`, and `check_subdomain_available` tests a subdomain before you try. A locked site refuses the change. See [Your free web address](https://modulify.ai/docs/publish/your-web-address#changing-the-subdomain).

## Inputs

| Input | Type | Required | Description |
| --- | --- | --- | --- |
| `projectId` | string | Yes | The site id. |
| `subdomain` | string | Yes | The new address, without the `.modulify.website` suffix, for example `acme-bakery`. |