---
title: accept.encoding_lookup
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/functions/content-negotiation/accept-encoding-lookup
---

```
STRING accept.encoding_lookup(STRING requested_content_encodings, STRING default, STRING accept_header)
```

**Available in:** all subroutines

Selects the best match from a string in the format of an `Accept-Encoding` 
header's value in the listed content encodings using the algorithm described 
in Section 5.3.3 of 
[RFC 7231](https://httpwg.org/specs/rfc7231.html#rfc.section.5.3.3).

This function takes the following parameters:

1. a colon-separated list of content encodings available for the resource,
2. a fallback return value,
3. a string representing an `Accept-Encoding` header's value.

This function does not have special handling of `x-compress` or `x-gzip` values.

## Example

```vcl
set bereq.http.Accept-Encoding =
  accept.encoding_lookup("compress:gzip", "identity",
    req.http.Accept-Encoding);
```