51Degrees API Documentation  4.4


User-Agent Client Hints (UA-CH) are part of a Google proposal to replace the existing User-Agent HTTP header.

This page gives an overview of UA-CH detection in our API and guidance on which of several possible mechanisms to use based on your use-case.

There are two ways to retrieve UA-CH values. You can either set HTTP headers in your response to the user's browser to ask it to send UA-CH values as HTTP headers, or you can use a JavaScript API to retrieve the UA-CH values on the client. See the Guidance section below if you're unsure which to use.

This topic has the following subpages:

  • Headers - How to use UA-CH HTTP headers with our API.
  • JavaScript - How to use the UA-CH JavaScript API with our API.
  • Required Values - Which UA-CH values do I need?

In addition, we have examples that demonstrate detection using UA-CH in a variety of scenarios:

The console examples pass UA-CH values directly to the API, so will work in any situation. The web examples run as a simple web page, so you will need a browser that supports UA-CH such as Chrome, Edge or other Chromium-based browsers in order to try them out.


Support for detection from Client Hints

The 51Degrees Device Detection API has provided support for detection based on one of the Client Hints headers (Sec-CH-UA) in data files from 7 December 2020. Full support for the detection of devices, operating systems, and browsers from UA-CH headers was added in Version 4.4 and data files from June 2022 onwards.

This support also includes identifying Windows 11 using User-Agent Client Hints as there is no other way to do so.

Support for getting values using the UA-CH JavaScript API was added in .NET API version 4.4.19 and data files from 6th March 2023. (Dates for availability in other APIs TBC)



UA-CH has several different mechanisms for accessing these values. This section explains our recommendations for different use-cases.

  • Our Pipeline API is running on-premise on the web server sending responses to the end-user:
    • If you are using our web integration, ensure the SetHeaderBrowserAccept-CH, SetHeaderHardwareAccept-CH and SetHeaderPlatformAccept-CH properties are included (all properties are included by default for on-premise). Our software will ensure the Accept-CH header is set to request the client hints you need from the browser.
    • If you are not using our web integration, see the 'non-integrated' section on the UA-CH Headers page
  • Our Pipeline API is running on-premise as part of a system that is not serving responses to end-users directly:
    • Ideally, we recommend you ask your clients to set Delegate-CH meta http-equiv tag or set the Permissions-Policy and Accept-CH response headers. This will allow their user's browser to send UA-CH values to your service. See the 'B2B service supplier' section on the UA-CH Headers page for instructions.
    • If the above is not feasible, and/or you want a backup option in case your clients do not implement the required changes, then you can use the UA-CH JavaScript API to retrieve the values. See the 'non-integrated' section on the UA-CH JavaScript page for instructions.
  • Calling our cloud service from client-side code:
    • For best performance, set Delegate-CH meta http-equiv tag or Permissions-Policy and Accept-CH response headers as described in the 'Cloud' section on the UA-CH Headers page
    • If making the changes for the option above is not feasible, you can simply ensure your Resource Key includes the JavascriptGetHighEntropyValues property. This will gather the values and send them to our cloud service without any other changes required.


Background reading

The authors of the proposal have created an article covering how UA-CH works. 51Degrees has blogged extensively on the subject. We also have an explainer and a test page that shows how UA-CH headers interact with the Accept-CH and Permissions-Policy response headers.

In May 2021, Google outlined their plans for the rollout of UA-CH. This also mentioned that the deprecation of the existing User-Agent will not happen until at least 2022. In September 2021, there was further detail about the plan for the phased deprecation of the User-Agent. This will start with Chrome 101 (roughly Q2 2022) and end with Chrome 113 (roughly Q2 2023).

User-Agent Client Hints extends the previously existing Client Hints content negotiation feature.

There is documentation of the general Client Hints feature on MDN and from Google.

Caniuse.com can be used to check browser support for both Client Hints and User-Agent Client Hints.

Finally, on 28 September 2022, we hosted a webinar discussing User-Agent Client Hints and the future of the User-Agent. Watch the webinar recording here.