index.md

---

title: ECT
slug: Web/HTTP/Headers/ECT
status:
  - experimental
browser-compat: http.headers.ect

---

{{HTTPSidebar}} {{SeeCompatTable}}

The ECT Client hint request header field indicates the {{Glossary("effective connection type")}}: slow-2g, 2g, 3g, 4g.

Header type	{{Glossary("Request header")}}, Client hint
{{Glossary("Forbidden header name")}}	no

The value represents the "network profile" that best matches the connection's latency and bandwidth, rather than the actual mechanisms used for transferring the data. For example, 2g might be used to represent a slow Wi-Fi connection with high latency and low bandwidth, while 4g might be used to represent a fast fibre-based broadband network.

The hint allows a server to choose what information is sent based on the broad characteristics of the network. For example, a server might choose to send smaller versions of images and other resources on less capable connections. The value might also be used as a starting point for determining what information is sent, which is further refined using information in {{HTTPHeader("RTT")}} and {{HTTPHeader("Downlink")}} hints.

Note: A server that specifies {{HTTPHeader("ECT")}} in {{HTTPHeader("Accept-CH")}} may also specify it in {{HTTPHeader("Vary")}} to indicate that responses should be cached for different ECT values.

Syntax

ECT: <value>

Directives

• <value>

  • : A value indicating {{Glossary("effective connection type")}}. This is one of: slow-2g, 2g, 3g, or 4g.

Examples

A server first needs to opt in to receive the ECT header by sending the {{HTTPHeader("Accept-CH")}} response header containing ECT.

Accept-CH: ECT

Then on subsequent requests the client might send an ECT header back:

ECT: 2g

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• Improving user privacy and developer experience with User-Agent Client Hints (web.dev)

• Network client hints

  • {{HTTPHeader("Downlink")}}

  • {{HTTPHeader("RTT")}}

  • {{HTTPHeader("Save-Data")}}

• {{HTTPHeader("Accept-CH")}}

• HTTP Caching > Varying responses and {{HTTPHeader("Vary")}}

• {{domxref("NetworkInformation.effectiveType")}}