---
title: synthetic.base64
summary: null
url: https://www.fastly.com/documentation/reference/vcl/statements/synthetic-base64
---

```
synthetic.base64(STRING content);
```

**Available in:** error

The `synthetic.base64` statement replaces the content of the cache object's response body with the specified string, when processing an error state. The argument is treated as base64-encoded and decoded, the resulting bytes are passed into the output buffer. Since the decoded data never exists as a `STRING` type, this statement is safe to use with non-textual data, such as images.

> **HINT:** To learn about using `synthetic.base64` to deliver custom responses at the edge, see the `error` statement.

Typically, synthetic responses are used to create customized error messages or responses to API calls, but can be used to serve full pages of content, favicons or small images.