---
title: Header reference
summary: null
url: https://www.fastly.com/documentation/reference/http/http-headers
---

Fastly cache servers read and write HTTP headers as part of the process of caching and routing requests and responses. This section defines all the headers that are meaningful to Fastly and how they affect the way a Fastly service will behave.

### Edge Platform

- [Accept](https://www.fastly.com/documentation/reference/http/http-headers/Accept/)
- [Accept-Encoding](https://www.fastly.com/documentation/reference/http/http-headers/Accept-Encoding/)
- [Accept-Language](https://www.fastly.com/documentation/reference/http/http-headers/Accept-Language/)
- [Age](https://www.fastly.com/documentation/reference/http/http-headers/Age/)
- [Alt-Svc](https://www.fastly.com/documentation/reference/http/http-headers/Alt-Svc/)
- [Cache-Control](https://www.fastly.com/documentation/reference/http/http-headers/Cache-Control/)
- [CDN-Loop](https://www.fastly.com/documentation/reference/http/http-headers/CDN-Loop/)
- [Content-Length](https://www.fastly.com/documentation/reference/http/http-headers/Content-Length/)
- [Content-Range](https://www.fastly.com/documentation/reference/http/http-headers/Content-Range/)
- [Cookie](https://www.fastly.com/documentation/reference/http/http-headers/Cookie/)
- [Date](https://www.fastly.com/documentation/reference/http/http-headers/Date/)
- [Expect](https://www.fastly.com/documentation/reference/http/http-headers/Expect/)
- [Expires](https://www.fastly.com/documentation/reference/http/http-headers/Expires/)
- [Fastly-Cachetype](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Cachetype/)
- [Fastly-Client](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Client/)
- [Fastly-Client-IP](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Client-IP/)
- [Fastly-Cookie-Overflow](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Cookie-Overflow/)
- [Fastly-Debug](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug/)
- [Fastly-Debug-Digest](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug-Digest/)
- [Fastly-Debug-Path](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug-Path/)
- [Fastly-Debug-TTL](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug-TTL/)
- [Fastly-FF](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-FF/)
- [Fastly-Force-Shield](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Force-Shield/)
- [Fastly-IO-Error](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-IO-Error/)
- [Fastly-IO-Info](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-IO-Info/)
- [Fastly-IO-Warning](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-IO-Warning/)
- [Fastly-Key](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Key/)
- [Fastly-No-Shield](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-No-Shield/)
- [Fastly-SSL](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-SSL/)
- [Fastly-Stats](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Stats/)
- [Host](https://www.fastly.com/documentation/reference/http/http-headers/Host/)
- [Proxy-Authenticate](https://www.fastly.com/documentation/reference/http/http-headers/Proxy-Authenticate/)
- [Proxy-Authorization](https://www.fastly.com/documentation/reference/http/http-headers/Proxy-Authorization/)
- [Surrogate-Control](https://www.fastly.com/documentation/reference/http/http-headers/Surrogate-Control/)
- [Surrogate-Key](https://www.fastly.com/documentation/reference/http/http-headers/Surrogate-Key/)
- [TE](https://www.fastly.com/documentation/reference/http/http-headers/TE/)
- [Trailer](https://www.fastly.com/documentation/reference/http/http-headers/Trailer/)
- [Transfer-Encoding](https://www.fastly.com/documentation/reference/http/http-headers/Transfer-Encoding/)
- [Upgrade](https://www.fastly.com/documentation/reference/http/http-headers/Upgrade/)
- [Vary](https://www.fastly.com/documentation/reference/http/http-headers/Vary/)
- [X-Cache](https://www.fastly.com/documentation/reference/http/http-headers/X-Cache/)
- [X-Cache-Hits](https://www.fastly.com/documentation/reference/http/http-headers/X-Cache-Hits/)
- [X-Compress-Hint](https://www.fastly.com/documentation/reference/http/http-headers/X-Compress-Hint/)
- [X-Fastly-Imageopto-API](https://www.fastly.com/documentation/reference/http/http-headers/X-Fastly-Imageopto-API/)
- [X-Fastly-Imageopto-Montage](https://www.fastly.com/documentation/reference/http/http-headers/X-Fastly-Imageopto-Montage/)
- [X-Fastly-Imageopto-Overlay](https://www.fastly.com/documentation/reference/http/http-headers/X-Fastly-Imageopto-Overlay/)
- [X-Forwarded-For](https://www.fastly.com/documentation/reference/http/http-headers/X-Forwarded-For/)
- [X-Forwarded-Host](https://www.fastly.com/documentation/reference/http/http-headers/X-Forwarded-Host/)
- [X-Forwarded-Server](https://www.fastly.com/documentation/reference/http/http-headers/X-Forwarded-Server/)
- [X-Served-By](https://www.fastly.com/documentation/reference/http/http-headers/X-Served-By/)
- [X-Timer](https://www.fastly.com/documentation/reference/http/http-headers/X-Timer/)
- [X-Varnish](https://www.fastly.com/documentation/reference/http/http-headers/X-Varnish/)

### API

- [Accept](https://www.fastly.com/documentation/reference/http/http-headers/Accept/)
- [Accept-Encoding](https://www.fastly.com/documentation/reference/http/http-headers/Accept-Encoding/)
- [Accept-Language](https://www.fastly.com/documentation/reference/http/http-headers/Accept-Language/)
- [Age](https://www.fastly.com/documentation/reference/http/http-headers/Age/)
- [Alt-Svc](https://www.fastly.com/documentation/reference/http/http-headers/Alt-Svc/)
- [Cache-Control](https://www.fastly.com/documentation/reference/http/http-headers/Cache-Control/)
- [CDN-Loop](https://www.fastly.com/documentation/reference/http/http-headers/CDN-Loop/)
- [Content-Length](https://www.fastly.com/documentation/reference/http/http-headers/Content-Length/)
- [Content-Range](https://www.fastly.com/documentation/reference/http/http-headers/Content-Range/)
- [Cookie](https://www.fastly.com/documentation/reference/http/http-headers/Cookie/)
- [Date](https://www.fastly.com/documentation/reference/http/http-headers/Date/)
- [Expect](https://www.fastly.com/documentation/reference/http/http-headers/Expect/)
- [Expires](https://www.fastly.com/documentation/reference/http/http-headers/Expires/)
- [Fastly-Cachetype](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Cachetype/)
- [Fastly-Client](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Client/)
- [Fastly-Client-IP](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Client-IP/)
- [Fastly-Cookie-Overflow](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Cookie-Overflow/)
- [Fastly-Debug](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug/)
- [Fastly-Debug-Digest](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug-Digest/)
- [Fastly-Debug-Path](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug-Path/)
- [Fastly-Debug-TTL](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug-TTL/)
- [Fastly-FF](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-FF/)
- [Fastly-Force-Shield](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Force-Shield/)
- [Fastly-IO-Error](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-IO-Error/)
- [Fastly-IO-Info](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-IO-Info/)
- [Fastly-IO-Warning](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-IO-Warning/)
- [Fastly-Key](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Key/)
- [Fastly-No-Shield](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-No-Shield/)
- [Fastly-SSL](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-SSL/)
- [Fastly-Stats](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Stats/)
- [Host](https://www.fastly.com/documentation/reference/http/http-headers/Host/)
- [Proxy-Authenticate](https://www.fastly.com/documentation/reference/http/http-headers/Proxy-Authenticate/)
- [Proxy-Authorization](https://www.fastly.com/documentation/reference/http/http-headers/Proxy-Authorization/)
- [Surrogate-Control](https://www.fastly.com/documentation/reference/http/http-headers/Surrogate-Control/)
- [Surrogate-Key](https://www.fastly.com/documentation/reference/http/http-headers/Surrogate-Key/)
- [TE](https://www.fastly.com/documentation/reference/http/http-headers/TE/)
- [Trailer](https://www.fastly.com/documentation/reference/http/http-headers/Trailer/)
- [Transfer-Encoding](https://www.fastly.com/documentation/reference/http/http-headers/Transfer-Encoding/)
- [Upgrade](https://www.fastly.com/documentation/reference/http/http-headers/Upgrade/)
- [Vary](https://www.fastly.com/documentation/reference/http/http-headers/Vary/)
- [X-Cache](https://www.fastly.com/documentation/reference/http/http-headers/X-Cache/)
- [X-Cache-Hits](https://www.fastly.com/documentation/reference/http/http-headers/X-Cache-Hits/)
- [X-Compress-Hint](https://www.fastly.com/documentation/reference/http/http-headers/X-Compress-Hint/)
- [X-Fastly-Imageopto-API](https://www.fastly.com/documentation/reference/http/http-headers/X-Fastly-Imageopto-API/)
- [X-Fastly-Imageopto-Montage](https://www.fastly.com/documentation/reference/http/http-headers/X-Fastly-Imageopto-Montage/)
- [X-Fastly-Imageopto-Overlay](https://www.fastly.com/documentation/reference/http/http-headers/X-Fastly-Imageopto-Overlay/)
- [X-Forwarded-For](https://www.fastly.com/documentation/reference/http/http-headers/X-Forwarded-For/)
- [X-Forwarded-Host](https://www.fastly.com/documentation/reference/http/http-headers/X-Forwarded-Host/)
- [X-Forwarded-Server](https://www.fastly.com/documentation/reference/http/http-headers/X-Forwarded-Server/)
- [X-Served-By](https://www.fastly.com/documentation/reference/http/http-headers/X-Served-By/)
- [X-Timer](https://www.fastly.com/documentation/reference/http/http-headers/X-Timer/)
- [X-Varnish](https://www.fastly.com/documentation/reference/http/http-headers/X-Varnish/)

### Media Products

- [Accept](https://www.fastly.com/documentation/reference/http/http-headers/Accept/)
- [Accept-Encoding](https://www.fastly.com/documentation/reference/http/http-headers/Accept-Encoding/)
- [Accept-Language](https://www.fastly.com/documentation/reference/http/http-headers/Accept-Language/)
- [Age](https://www.fastly.com/documentation/reference/http/http-headers/Age/)
- [Alt-Svc](https://www.fastly.com/documentation/reference/http/http-headers/Alt-Svc/)
- [Cache-Control](https://www.fastly.com/documentation/reference/http/http-headers/Cache-Control/)
- [CDN-Loop](https://www.fastly.com/documentation/reference/http/http-headers/CDN-Loop/)
- [Content-Length](https://www.fastly.com/documentation/reference/http/http-headers/Content-Length/)
- [Content-Range](https://www.fastly.com/documentation/reference/http/http-headers/Content-Range/)
- [Cookie](https://www.fastly.com/documentation/reference/http/http-headers/Cookie/)
- [Date](https://www.fastly.com/documentation/reference/http/http-headers/Date/)
- [Expect](https://www.fastly.com/documentation/reference/http/http-headers/Expect/)
- [Expires](https://www.fastly.com/documentation/reference/http/http-headers/Expires/)
- [Fastly-Cachetype](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Cachetype/)
- [Fastly-Client](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Client/)
- [Fastly-Client-IP](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Client-IP/)
- [Fastly-Cookie-Overflow](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Cookie-Overflow/)
- [Fastly-Debug](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug/)
- [Fastly-Debug-Digest](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug-Digest/)
- [Fastly-Debug-Path](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug-Path/)
- [Fastly-Debug-TTL](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Debug-TTL/)
- [Fastly-FF](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-FF/)
- [Fastly-Force-Shield](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Force-Shield/)
- [Fastly-IO-Error](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-IO-Error/)
- [Fastly-IO-Info](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-IO-Info/)
- [Fastly-IO-Warning](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-IO-Warning/)
- [Fastly-Key](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Key/)
- [Fastly-No-Shield](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-No-Shield/)
- [Fastly-SSL](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-SSL/)
- [Fastly-Stats](https://www.fastly.com/documentation/reference/http/http-headers/Fastly-Stats/)
- [Host](https://www.fastly.com/documentation/reference/http/http-headers/Host/)
- [Proxy-Authenticate](https://www.fastly.com/documentation/reference/http/http-headers/Proxy-Authenticate/)
- [Proxy-Authorization](https://www.fastly.com/documentation/reference/http/http-headers/Proxy-Authorization/)
- [Surrogate-Control](https://www.fastly.com/documentation/reference/http/http-headers/Surrogate-Control/)
- [Surrogate-Key](https://www.fastly.com/documentation/reference/http/http-headers/Surrogate-Key/)
- [TE](https://www.fastly.com/documentation/reference/http/http-headers/TE/)
- [Trailer](https://www.fastly.com/documentation/reference/http/http-headers/Trailer/)
- [Transfer-Encoding](https://www.fastly.com/documentation/reference/http/http-headers/Transfer-Encoding/)
- [Upgrade](https://www.fastly.com/documentation/reference/http/http-headers/Upgrade/)
- [Vary](https://www.fastly.com/documentation/reference/http/http-headers/Vary/)
- [X-Cache](https://www.fastly.com/documentation/reference/http/http-headers/X-Cache/)
- [X-Cache-Hits](https://www.fastly.com/documentation/reference/http/http-headers/X-Cache-Hits/)
- [X-Compress-Hint](https://www.fastly.com/documentation/reference/http/http-headers/X-Compress-Hint/)
- [X-Fastly-Imageopto-API](https://www.fastly.com/documentation/reference/http/http-headers/X-Fastly-Imageopto-API/)
- [X-Fastly-Imageopto-Montage](https://www.fastly.com/documentation/reference/http/http-headers/X-Fastly-Imageopto-Montage/)
- [X-Fastly-Imageopto-Overlay](https://www.fastly.com/documentation/reference/http/http-headers/X-Fastly-Imageopto-Overlay/)
- [X-Forwarded-For](https://www.fastly.com/documentation/reference/http/http-headers/X-Forwarded-For/)
- [X-Forwarded-Host](https://www.fastly.com/documentation/reference/http/http-headers/X-Forwarded-Host/)
- [X-Forwarded-Server](https://www.fastly.com/documentation/reference/http/http-headers/X-Forwarded-Server/)
- [X-Served-By](https://www.fastly.com/documentation/reference/http/http-headers/X-Served-By/)
- [X-Timer](https://www.fastly.com/documentation/reference/http/http-headers/X-Timer/)
- [X-Varnish](https://www.fastly.com/documentation/reference/http/http-headers/X-Varnish/)

## Reading and setting HTTP headers

In [VCL](https://www.fastly.com/documentation/guides/full-site-delivery/fastly-vcl/about-fastly-vcl), it's possible to read and write HTTP headers on the incoming client request (`req.http.{NAME}`), the request to the backend (`bereq.http.{NAME}`), the response from the backend (`beresp.http.{NAME}`), or the response to the client (`resp.http.{NAME}`). It's also possible to read and write headers on a cache object (`obj.http.{NAME}`) in some parts of the VCL flow.

To set the value of a header, use the `set` or `add` statements:

```vcl
set req.http.Custom-Header = "some=1, data=2, here=3";
set req.http.Another-Header = "header-values-can-be-any-string-data";
```

While you can set the value of a header in any format you like, using [structured fields](https://tools.ietf.org/html/draft-ietf-httpbis-header-structure-19) is a good way to make the values easier to parse later. In fact, if you use this format, you can access subfields using a convenience syntax in VCL:

```vcl
set req.http.Cache-Control:max-age = "3600";
```

This subfield accessor syntax also works for reading headers:

```vcl
if (req.http.cookie:cookie-name) {
  # Do something with the 'cookie-name' cookie
}
```

Some headers, such as `Vary`, take a list of keys (in the case of `Vary`, a list of other header names), but no values. Subfield syntax can be used to add or remove keys from these kinds of headers:

```vcl
set resp.http.Vary:Accept-Encoding = ""; // Add "Accept-Encoding" to the Vary header
unset resp.http.Vary:User-Agent;         // Remove "User-Agent" from the Vary header
```