---
title: Create a custom 404 page
description: Replace the default 404 page with branded content written in MDX.
url: https://pr-7-a9c4e9fe1b6c.thally.app/guides/custom-404
---
# Create a custom 404 page
Replace the default 404 page with branded content written in MDX.
By default, Thally shows a built-in "Page not found" screen when a URL doesn't match any content. You can replace it with your own branded 404 page written in MDX.
## Creating a custom 404
Create a file at `src/content/404.mdx`:
```mdx
---
title: Page Not Found
description: We couldn't find what you were looking for.
---
# 404 — Page not found
Looks like this page has moved or no longer exists.
Return to the documentation home.
Try searching for what you need.
```
Thally automatically detects this file and renders it through the standard MDX pipeline — so all components (``, ``, etc.) work normally.
## Fallback behavior
If `src/content/404.mdx` does not exist, Thally renders its built-in 404 UI. You can always delete or rename `404.mdx` to revert to the default.
## Frontmatter
The `title` and `description` frontmatter fields are used for the page `` and OG metadata. The `mode` field also works — use `mode: "center"` for a clean centered layout.
```mdx
---
title: Page Not Found
description: We couldn't find that page.
mode: center
---
```
> **Note:**
The 404 page does not appear in the sidebar or sitemap. It is automatically given a `noindex` robots tag.