From f01756f5a72211d766f18fb5830384ec32f1693f Mon Sep 17 00:00:00 2001 From: Barry Pollard Date: Thu, 29 Jan 2026 18:34:19 +0000 Subject: [PATCH 1/6] Reorganise the spec --- index.bs | 159 ++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 98 insertions(+), 61 deletions(-) diff --git a/index.bs b/index.bs index a3581dc..feb6c72 100644 --- a/index.bs +++ b/index.bs @@ -10,7 +10,7 @@ Editor: Barry Pollard, Google https://google.com, barrypollard@google.com, w3cid Editor: Guohui Deng, Microsoft https://microsoft.com, guohuideng@microsoft.com, w3cid 158258 Former Editor: Shubhie Panicker, Google https://google.com Repository: w3c/device-memory -Abstract: This document defines a HTTP Client Hint header and a JavaScript API to surface device capability for memory i.e. device RAM, in order to enable web apps to customize content depending on device memory constraints. +Abstract: This document defines a HTTP Client Hint header and a JavaScript API to surface device capability for memory (device RAM) in order to enable web apps to customize content depending on device memory constraints. Required IDs: sec-device-memory-client-hint-header Default Highlight: js @@ -27,72 +27,81 @@ urlPrefix: https://datatracker.ietf.org/doc/html/rfc8941; spec: rfc8942 text: HTTP Client Hint; url: #name-introduction -Introduction {#intro} -===================== -Developers need device-class signal for: -1. Serving light version of the site or specific components, for low-end devices. Examples: - * Serve Google "search lite" - a 10KB search results page used in EM. - * Serve a light version of video player in Facebook. - * Serve lightweight tile images in Google Maps. +

Introduction

-2. Normalizing Metrics: analytics need to be able to normalize their metrics against the device-class. For instance, a 100ms long task on a high end device is a more severe issue compared to a low-end device. +A device-class signal is used for several reasons, including: -Device memory is an especially useful signal for determining “device-class”. Low memory devices devices (under 512MB, 512MB - 1GB) are widely used in emerging markets. +- Serving a light version of the site or specific components: This is useful to customize a site for low-end devices. Examples include: + - Serve “search lite” - a 10KB search results page used for low-end devices. + - Serve a light version of video player in a social media web application. + - Serve lightweight tile images in a map web application. -Usage Example {#example} ------------------------- -A server opts in to receive a Sec-CH-Device-Memory [=HTTP Client Hint=] using the Accept-CH header field, or an equivalent HTML meta element with http-equiv attribute: +- Normalizing metrics: analytics need to be able to normalize their metrics against the device-class. For instance, a 100ms long task on a high end device is a more severe issue compared to a low-end device. -
-    Accept-CH: Sec-CH-Device-Memory
-
+Device identification and classification based on advertised User-Agent, and other characteristics of the client, are commonly used to select and provide optimized content. Such solutions frequently rely on commercial device databases, which are costly, hard to integrate, and hard to maintain. -In turn, on receiving the above preferences from the server, a compatible user agent would then advertise the device capability for memory, via the Sec-CH-Device-Memory request header field: +This specification defines a (Client Hint) Header Field and a JavaScript API which exposes the approximate device memory (RAM) to address these needs without needing to use a device database. -
-    GET /example HTTP/1.1
-    Sec-CH-Device-Memory: 0.5
-    ...
-
+

Computing device memory value

+ +
+ The deviceMemory getter steps are: -Sec-CH-Device-Memory (Client Hint) Header Field {#sec-device-memory-client-hint-header} -======================================= + 1. Let |physicalDeviceMemory| be the amount of physical memory in bytes. + 2. Let |minimumLowerBound| be an implementation-specific minimum reported value. + 3. Let |maximumUpperBound| be an implementation-specific maximum reported value. + 4. Let |deviceMemory| be |physicalDeviceMemory|. + 5. Let |power| be 0. + 6. [=iteration/While=] |deviceMemory| is greater than 0: + 1. Bitwise shift |deviceMemory| right 1 place. + 2. Increment |power| by 1. + 7. Let |lowerBound| be 1 to the power of |power|. + 8. Let |upperBound| be 2 to the power of |power|. + 9. If |physicalDeviceMemory| - |lowerBound| <= |physicalDeviceMemory| - |upperBound|, then |deviceMemory|'s value is |lowerBound|. + 10. Otherwise |deviceMemory|'s value is |upperBound|. + 11. |deviceMemory| is |deviceMemory| / 1024.0. + 12. If |deviceMemory| < |minimumLowerBound|, then |deviceMemory| is |minimumLowerBound|. + 13. If |deviceMemory| > |maximumUpperBound|, then |deviceMemory| is |maximumUpperBound|. + 14. Return |deviceMemory|. +
+ +Note: The algorithm includes the ability for implementation-specific upper bound and a lower bounds. The range between the upper and the lower bounds should include the majority of device memory values but exclude rare device memory values to mitigate device fingerprinting. Implementations may adjust these bounds over time. These bounds may differ on different device types. + +

Sec-CH-Device-Memory (Client Hint) Header Field

The Sec-CH-Device-Memory header field is a [=HTTP Client Hint=] header. -It is a [=structured header value=] containing an [=item=] which value is a [=decimal=] that indicates the client’s device memory, i.e. the approximate amount of RAM in GiB. +It is a [=structured header value=] containing an [=item=] which value is a [=decimal=] that indicates the client’s approximate amount of device memory (RAM) in GiB. + +If Sec-CH-Device-Memory header field occurs in a message more than once, the last value overrides all previous occurrences. The ABNF (Augmented Backus-Naur Form) syntax for the Sec-CH-Device-Memory header field is as follows: ~~~ abnf - Sec-CH-Device-Memory = sf-decimal +Sec-CH-Device-Memory = sf-decimal ~~~ -

Computing Device Memory Value

-The value is calculated by using the actual device memory in MiB then rounding it to the nearest number where only the most significant bit can be set and the rest are zeros (nearest power of two). Then dividing that number by 1024.0 to get the value in GiB. - -An upper bound and a lower bound should be set on the list of values. The range between the upper and the lower bounds should include the majority of device memory values but exclude rare device memory values to mitigate device fingerprinting. - - NOTE: The Implementations may set upper and lower bounds and adjust them dynamically over time. These bounds may even differ on different device types. - -If Sec-CH-Device-Memory header field occurs in a message more than once, the last value overrides all previous occurrences. +The Sec-CH-Device-Memory's value should be set to [=this=]'s [=deviceMemory=] +

Client Hint examples

-

Examples

+
+ A server opts in to receive a Sec-CH-Device-Memory [=HTTP Client Hint=] using the Accept-CH header field, or an equivalent HTML meta element with http-equiv attribute: -512 MiB will be reported as: + 
+        Accept-CH: Sec-CH-Device-Memory
+
-
-    Sec-CH-Device-Memory: 0.5
-
+ In turn, on receiving the above preferences from the server, a compatible user agent would then advertise the device capability for memory, via the Sec-CH-Device-Memory request header field: -1000 MiB will be reported as: + 
+        GET /example HTTP/1.1
+        Sec-CH-Device-Memory: 8
+        ...
+
+
-
-    Sec-CH-Device-Memory: 1
-
+

Device Memory JavaScript API

-Device Memory JS API {#sec-device-memory-js-api} -======================================= 
 [
     SecureContext,
@@ -105,24 +114,56 @@ Navigator includes NavigatorDeviceMemory;
 WorkerNavigator includes NavigatorDeviceMemory;
- NOTE: self.navigator.deviceMemory Returns the amount of ram in GiB as described in [[#computing-device-memory-value]] +The deviceMemory getter steps are to return [=this=]'s [=deviceMemory=] + +

JavaScript examples

+ +
+ + A web application can either enable or disable features based on device memory. + + Note: The web application should consider how to handle browsers that do not support the API: either by enabling by default, or disabling by default. -Security Considerations {#sec-security-considerations} -======================================= + 
+        const mem = navigator.deviceMemory;
 
-Sec-CH-Device-Memory Client Hint header and JS API will only be available to HTTPS secure contexts.  
+        // Either disable features if it is known to be a low-memory device
+        if (mem && mem < 2) {
+            // disable features to provide a better experience
+        }
 
-Device identification and classification (e.g. device type and class) based on advertised User-Agent, and other characteristics of the client, are commonly used to select and provide optimized content. Such solutions frequently rely on commercial device databases, which are costly, hard to integrate, and hard to maintain. This specification defines a mechanism to obtain device memory capability that addresses these technical challenges.
+        // Or, alternatively only enable features if the device memory is
+        // either not provided, or known to be above minimum requirements
+        if (!mem || mem > 4) {
+            // enable features to provide a better experience
+        }
+
+
-To reduce fingerprinting risk, reported value is rounded to single most significant bit, as opposed to reporting the exact value. In addition, an upper and lower bound is placed on the reported values. +
+ A RUM solution can query the device memory using navigator.deviceMemory API and include this in performance beacons as additional information to help explain or segment the data. -IANA considerations {#iana} -=================== + 
+        const mem = navigator.deviceMemory;
+        const analyticsData = {
+            memory: mem;
+            ... other metrics
+        }
+        navigator.sendBeacon("/endpoint", analyticsData);
+
+
+ +

Security & privacy considerations

+ +Sec-CH-Device-Memory Client Hint header and JavaScript API will only be available to HTTPS secure contexts. + +To reduce fingerprinting risk, the reported value is rounded to a single significant bit, as opposed to reporting the exact value. In addition, an implementation-specific upper and lower bound is placed on the reported values. These bounds should be reviewed over time as commonly used device memory characteristics change. Device type should be taken into account when defining these bounds since mobile devices typically have different characteristics than desktops and laptops. + +

IANA considerations

This document defines the Sec-CH-Device-Memory HTTP request header field, and registers them in the permanent message header field registry ([[RFC3864]]). -Sec-CH-Device-Memory Header field {#iana-device-memory} ---------------------------------- +

Sec-CH-Device-Memory Header field

: Header field name :: Sec-CH-Device-Memory @@ -139,10 +180,6 @@ Sec-CH-Device-Memory Header field {#iana-device-memory} : Specification document :: this specification ([[#sec-device-memory-client-hint-header]]) - -

Acknowledgements

- - +

Acknowledgements

-Special thanks to all the contributors for their technical input and suggestions that led to improvements to this -specification. +Special thanks to the previous editor Shubhie Panicker and all the contributors for their technical input and suggestions that led to improvements to this specification. From e6024d3fd7c84340b9ebe6d22d9f14d054103975 Mon Sep 17 00:00:00 2001 From: Barry Pollard Date: Thu, 29 Jan 2026 18:56:24 +0000 Subject: [PATCH 2/6] Prefer markdown where possible --- index.bs | 85 ++++++++++++++++++++++++++++++++------------------------ 1 file changed, 48 insertions(+), 37 deletions(-) diff --git a/index.bs b/index.bs index feb6c72..e272448 100644 --- a/index.bs +++ b/index.bs @@ -13,6 +13,7 @@ Repository: w3c/device-memory Abstract: This document defines a HTTP Client Hint header and a JavaScript API to surface device capability for memory (device RAM) in order to enable web apps to customize content depending on device memory constraints. Required IDs: sec-device-memory-client-hint-header Default Highlight: js +Markup Shorthands: markdown yes 
@@ -27,22 +28,24 @@ urlPrefix: https://datatracker.ietf.org/doc/html/rfc8941; spec: rfc8942
         text: HTTP Client Hint; url: #name-introduction
-

Introduction

+Introduction {#intro} +============ A device-class signal is used for several reasons, including: -- Serving a light version of the site or specific components: This is useful to customize a site for low-end devices. Examples include: +- **Serving a light version of the site or specific components**: This is useful to customize a site for low-end devices. Examples include: - Serve “search lite” - a 10KB search results page used for low-end devices. - Serve a light version of video player in a social media web application. - Serve lightweight tile images in a map web application. -- Normalizing metrics: analytics need to be able to normalize their metrics against the device-class. For instance, a 100ms long task on a high end device is a more severe issue compared to a low-end device. +- **Normalizing metrics**: analytics need to be able to normalize their metrics against the device-class. For instance, a 100ms long task on a high end device is a more severe issue compared to a low-end device. -Device identification and classification based on advertised User-Agent, and other characteristics of the client, are commonly used to select and provide optimized content. Such solutions frequently rely on commercial device databases, which are costly, hard to integrate, and hard to maintain. +Device identification and classification based on advertised `User-Agent`, and other characteristics of the client, are commonly used to select and provide optimized content. Such solutions frequently rely on commercial device databases, which are costly, hard to integrate, and hard to maintain. -This specification defines a (Client Hint) Header Field and a JavaScript API which exposes the approximate device memory (RAM) to address these needs without needing to use a device database. +This specification defines a [(Client Hint) Header Field](#sec-device-memory-client-hint-header) and a [JavaScript API](#device-memory-js-api) which exposes the approximate device memory (RAM) to address these needs without needing to use a device database. -

Computing device memory value

+Computing device memory value {#computing-device-memory} +=============================
The deviceMemory getter steps are: @@ -67,42 +70,45 @@ This specification defines a (Cl Note: The algorithm includes the ability for implementation-specific upper bound and a lower bounds. The range between the upper and the lower bounds should include the majority of device memory values but exclude rare device memory values to mitigate device fingerprinting. Implementations may adjust these bounds over time. These bounds may differ on different device types. -

Sec-CH-Device-Memory (Client Hint) Header Field

+`Sec-CH-Device-Memory` (Client Hint) Header Field {#sec-device-memory-client-hint-header} +============================================================ -The Sec-CH-Device-Memory header field is a [=HTTP Client Hint=] header. +The `Sec-CH-Device-Memory` header field is a [=HTTP Client Hint=] header. It is a [=structured header value=] containing an [=item=] which value is a [=decimal=] that indicates the client’s approximate amount of device memory (RAM) in GiB. -If Sec-CH-Device-Memory header field occurs in a message more than once, the last value overrides all previous occurrences. +If `Sec-CH-Device-Memory` header field occurs in a message more than once, the last value overrides all previous occurrences. -The ABNF (Augmented Backus-Naur Form) syntax for the Sec-CH-Device-Memory header field is as follows: +The ABNF (Augmented Backus-Naur Form) syntax for the `Sec-CH-Device-Memory` header field is as follows: -~~~ abnf +```abnf Sec-CH-Device-Memory = sf-decimal -~~~ +``` -The Sec-CH-Device-Memory's value should be set to [=this=]'s [=deviceMemory=] +The `Sec-CH-Device-Memory`'s value should be set to [=this=]'s [=deviceMemory=] -

Client Hint examples

+Client Hint examples {#client-hint-examples} +--------------------
- A server opts in to receive a Sec-CH-Device-Memory [=HTTP Client Hint=] using the Accept-CH header field, or an equivalent HTML meta element with http-equiv attribute: + A server opts in to receive a `Sec-CH-Device-Memory` [=HTTP Client Hint=] using the `Accept-CH` header field, or an equivalent HTML meta element with http-equiv attribute: - 
+    ```http
         Accept-CH: Sec-CH-Device-Memory
-
+ ``` - In turn, on receiving the above preferences from the server, a compatible user agent would then advertise the device capability for memory, via the Sec-CH-Device-Memory request header field: + In turn, on receiving the above preferences from the server, a compatible user agent would then advertise the device capability for memory, via the `Sec-CH-Device-Memory` request header field: - 
+    ```http
         GET /example HTTP/1.1
         Sec-CH-Device-Memory: 8
         ...
-
+ ```
-

Device Memory JavaScript API

+Device Memory JavaScript API {#device-memory-js-api} +============================ -
+```idl
 [
     SecureContext,
     Exposed=(Window,Worker)
@@ -112,11 +118,12 @@ The Sec-CH-Device-Memory's value should be set to [=this=]'s [=devi
 
 Navigator includes NavigatorDeviceMemory;
 WorkerNavigator includes NavigatorDeviceMemory;
-
+``` -The deviceMemory getter steps are to return [=this=]'s [=deviceMemory=] +The `deviceMemory` getter steps are to return [=this=]'s [=deviceMemory=] -

JavaScript examples

+JavaScript examples {#javascript-examples} +-------------------
@@ -124,7 +131,7 @@ The deviceMemory getter steps are to return [=this=]'s [=deviceMemo Note: The web application should consider how to handle browsers that do not support the API: either by enabling by default, or disabling by default. - 
+    ```javascript
         const mem = navigator.deviceMemory;
 
         // Either disable features if it is known to be a low-memory device
@@ -137,33 +144,36 @@ The deviceMemory getter steps are to return [=this=]'s [=deviceMemo
         if (!mem || mem > 4) {
             // enable features to provide a better experience
         }
-
+ ```
- A RUM solution can query the device memory using navigator.deviceMemory API and include this in performance beacons as additional information to help explain or segment the data. + A RUM solution can query the device memory using `navigator.deviceMemory` API and include this in performance beacons as additional information to help explain or segment the data. - 
+    ```javascript
         const mem = navigator.deviceMemory;
         const analyticsData = {
             memory: mem;
             ... other metrics
         }
         navigator.sendBeacon("/endpoint", analyticsData);
-
+ ```
-

Security & privacy considerations

+Security & privacy considerations {#security-and-privacy} +================================= -Sec-CH-Device-Memory Client Hint header and JavaScript API will only be available to HTTPS secure contexts. +`Sec-CH-Device-Memory` Client Hint header and JavaScript API will only be available to HTTPS secure contexts. To reduce fingerprinting risk, the reported value is rounded to a single significant bit, as opposed to reporting the exact value. In addition, an implementation-specific upper and lower bound is placed on the reported values. These bounds should be reviewed over time as commonly used device memory characteristics change. Device type should be taken into account when defining these bounds since mobile devices typically have different characteristics than desktops and laptops. -

IANA considerations

+IANA considerations {#iana} +=================== -This document defines the Sec-CH-Device-Memory HTTP request header field, and registers them in the permanent message header field registry ([[RFC3864]]). +This document defines the `Sec-CH-Device-Memory` HTTP request header field, and registers them in the permanent message header field registry ([[RFC3864]]). -

Sec-CH-Device-Memory Header field

+Sec-CH-Device-Memory Header field {#iana-device-memory} +================================= : Header field name :: Sec-CH-Device-Memory @@ -180,6 +190,7 @@ This document defines the Sec-CH-Device-Memory HTTP request header : Specification document :: this specification ([[#sec-device-memory-client-hint-header]]) -

Acknowledgements

+Acknowledgements {#acknowledgements} +================ -Special thanks to the previous editor Shubhie Panicker and all the contributors for their technical input and suggestions that led to improvements to this specification. +Special thanks to the previous editor Shubhie Panicker and [all the contributors](https://github.com/w3c/device-memory/graphs/contributors) for their technical input and suggestions that led to improvements to this specification. From 8c73260ee905ca06ee7b814a2c3cc81332cfaddf Mon Sep 17 00:00:00 2001 From: Barry Pollard Date: Thu, 29 Jan 2026 19:06:12 +0000 Subject: [PATCH 3/6] Markdown headings --- index.bs | 32 +++++++++++--------------------- 1 file changed, 11 insertions(+), 21 deletions(-) diff --git a/index.bs b/index.bs index e272448..b636bde 100644 --- a/index.bs +++ b/index.bs @@ -28,8 +28,7 @@ urlPrefix: https://datatracker.ietf.org/doc/html/rfc8941; spec: rfc8942 text: HTTP Client Hint; url: #name-introduction -Introduction {#intro} -============ +# Introduction # {#intro} A device-class signal is used for several reasons, including: @@ -44,8 +43,7 @@ Device identification and classification based on advertised `User-Agent`, and o This specification defines a [(Client Hint) Header Field](#sec-device-memory-client-hint-header) and a [JavaScript API](#device-memory-js-api) which exposes the approximate device memory (RAM) to address these needs without needing to use a device database. -Computing device memory value {#computing-device-memory} -============================= +# Computing device memory value # {#computing-device-memory}
The deviceMemory getter steps are: @@ -70,8 +68,7 @@ Computing device memory value {#computing-device-memory} Note: The algorithm includes the ability for implementation-specific upper bound and a lower bounds. The range between the upper and the lower bounds should include the majority of device memory values but exclude rare device memory values to mitigate device fingerprinting. Implementations may adjust these bounds over time. These bounds may differ on different device types. -`Sec-CH-Device-Memory` (Client Hint) Header Field {#sec-device-memory-client-hint-header} -============================================================ +# `Sec-CH-Device-Memory` (Client Hint) Header Field # {#sec-device-memory-client-hint-header} The `Sec-CH-Device-Memory` header field is a [=HTTP Client Hint=] header. It is a [=structured header value=] containing an [=item=] which value is a [=decimal=] that indicates the client’s approximate amount of device memory (RAM) in GiB. @@ -86,8 +83,7 @@ Sec-CH-Device-Memory = sf-decimal The `Sec-CH-Device-Memory`'s value should be set to [=this=]'s [=deviceMemory=] -Client Hint examples {#client-hint-examples} --------------------- +## Client Hint examples ## {#client-hint-examples}
A server opts in to receive a `Sec-CH-Device-Memory` [=HTTP Client Hint=] using the `Accept-CH` header field, or an equivalent HTML meta element with http-equiv attribute: @@ -105,8 +101,7 @@ Client Hint examples {#client-hint-examples} ```
-Device Memory JavaScript API {#device-memory-js-api} -============================ +# Device Memory JavaScript API # {#device-memory-js-api} ```idl [ @@ -122,8 +117,7 @@ WorkerNavigator includes NavigatorDeviceMemory; The `deviceMemory` getter steps are to return [=this=]'s [=deviceMemory=] -JavaScript examples {#javascript-examples} -------------------- +## JavaScript examples ## {#javascript-examples}
@@ -160,20 +154,17 @@ JavaScript examples {#javascript-examples} ```
-Security & privacy considerations {#security-and-privacy} -================================= +# Security & privacy considerations # {#security-and-privacy} `Sec-CH-Device-Memory` Client Hint header and JavaScript API will only be available to HTTPS secure contexts. To reduce fingerprinting risk, the reported value is rounded to a single significant bit, as opposed to reporting the exact value. In addition, an implementation-specific upper and lower bound is placed on the reported values. These bounds should be reviewed over time as commonly used device memory characteristics change. Device type should be taken into account when defining these bounds since mobile devices typically have different characteristics than desktops and laptops. -IANA considerations {#iana} -=================== +# IANA considerations # {#iana} This document defines the `Sec-CH-Device-Memory` HTTP request header field, and registers them in the permanent message header field registry ([[RFC3864]]). -Sec-CH-Device-Memory Header field {#iana-device-memory} -================================= +## `Sec-CH-Device-Memory` header field ## {#iana-device-memory} : Header field name :: Sec-CH-Device-Memory @@ -188,9 +179,8 @@ Sec-CH-Device-Memory Header field {#iana-device-memory} :: IETF : Specification document -:: this specification ([[#sec-device-memory-client-hint-header]]) +:: This specification ([[#sec-device-memory-client-hint-header]]) -Acknowledgements {#acknowledgements} -================ +# Acknowledgements # {#acknowledgements} Special thanks to the previous editor Shubhie Panicker and [all the contributors](https://github.com/w3c/device-memory/graphs/contributors) for their technical input and suggestions that led to improvements to this specification. From 05413854155e5149dc2514b7f604b8ed8d10be20 Mon Sep 17 00:00:00 2001 From: Barry Pollard Date: Wed, 25 Feb 2026 18:59:28 +0000 Subject: [PATCH 4/6] Review feedback --- index.bs | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-) diff --git a/index.bs b/index.bs index b636bde..2cf4705 100644 --- a/index.bs +++ b/index.bs @@ -46,19 +46,19 @@ This specification defines a [(Client Hint) Header Field](#sec-device-memory-cli # Computing device memory value # {#computing-device-memory}
- The deviceMemory getter steps are: + The [=user agent=]'s deviceMemory is calculated by these steps: 1. Let |physicalDeviceMemory| be the amount of physical memory in bytes. - 2. Let |minimumLowerBound| be an implementation-specific minimum reported value. - 3. Let |maximumUpperBound| be an implementation-specific maximum reported value. + 2. Let |minimumLowerBound| be an [=implementation-defined=] minimum bound. + 3. Let |maximumUpperBound| be an [=implementation-defined=] maximum bound. 4. Let |deviceMemory| be |physicalDeviceMemory|. 5. Let |power| be 0. 6. [=iteration/While=] |deviceMemory| is greater than 0: 1. Bitwise shift |deviceMemory| right 1 place. 2. Increment |power| by 1. - 7. Let |lowerBound| be 1 to the power of |power|. - 8. Let |upperBound| be 2 to the power of |power|. - 9. If |physicalDeviceMemory| - |lowerBound| <= |physicalDeviceMemory| - |upperBound|, then |deviceMemory|'s value is |lowerBound|. + 7. Let |lowerBound| be 2 to the power of |power|. + 8. Let |upperBound| be 2 to the power of |power + 1|. + 9. If |physicalDeviceMemory| − |lowerBound| ≤ |upperBound| − |physicalDeviceMemory|, then |deviceMemory|'s value is |lowerBound|. 10. Otherwise |deviceMemory|'s value is |upperBound|. 11. |deviceMemory| is |deviceMemory| / 1024.0. 12. If |deviceMemory| < |minimumLowerBound|, then |deviceMemory| is |minimumLowerBound|. @@ -66,33 +66,33 @@ This specification defines a [(Client Hint) Header Field](#sec-device-memory-cli 14. Return |deviceMemory|.
-Note: The algorithm includes the ability for implementation-specific upper bound and a lower bounds. The range between the upper and the lower bounds should include the majority of device memory values but exclude rare device memory values to mitigate device fingerprinting. Implementations may adjust these bounds over time. These bounds may differ on different device types. +The algorithm includes the ability for [=implementation-defined=] upper bound and a lower bounds. The range between the upper and the lower bounds should include the majority of device memory values but exclude rare device memory values to mitigate device fingerprinting. Implementations may adjust these bounds over time. These bounds may differ on different device types. # `Sec-CH-Device-Memory` (Client Hint) Header Field # {#sec-device-memory-client-hint-header} -The `Sec-CH-Device-Memory` header field is a [=HTTP Client Hint=] header. +The `Sec-CH-Device-Memory` header field is a [=HTTP Client Hint=] header. It is a [=structured header value=] containing an [=item=] which value is a [=decimal=] that indicates the client’s approximate amount of device memory (RAM) in GiB. -If `Sec-CH-Device-Memory` header field occurs in a message more than once, the last value overrides all previous occurrences. +If [:Sec-CH-Device-Memory:] header field occurs in a message more than once, the last value overrides all previous occurrences. -The ABNF (Augmented Backus-Naur Form) syntax for the `Sec-CH-Device-Memory` header field is as follows: +The ABNF (Augmented Backus-Naur Form) syntax for the [:Sec-CH-Device-Memory:] header field is as follows: ```abnf Sec-CH-Device-Memory = sf-decimal ``` -The `Sec-CH-Device-Memory`'s value should be set to [=this=]'s [=deviceMemory=] +The [:Sec-CH-Device-Memory:]'s value [=user agent=]'s [=deviceMemory=]. ## Client Hint examples ## {#client-hint-examples}
- A server opts in to receive a `Sec-CH-Device-Memory` [=HTTP Client Hint=] using the `Accept-CH` header field, or an equivalent HTML meta element with http-equiv attribute: + A server opts in to receive a [:Sec-CH-Device-Memory:] [=HTTP Client Hint=] using the `Accept-CH` header field, or an equivalent HTML meta element with http-equiv attribute: ```http Accept-CH: Sec-CH-Device-Memory ``` - In turn, on receiving the above preferences from the server, a compatible user agent would then advertise the device capability for memory, via the `Sec-CH-Device-Memory` request header field: + In turn, on receiving the above preferences from the server, a compatible user agent would then advertise the device capability for memory, via the [:Sec-CH-Device-Memory:] request header field: ```http GET /example HTTP/1.1 @@ -115,7 +115,7 @@ Navigator includes NavigatorDeviceMemory; WorkerNavigator includes NavigatorDeviceMemory; ``` -The `deviceMemory` getter steps are to return [=this=]'s [=deviceMemory=] +The [=NavigatorDeviceMemory=]'s [=NavigatorDeviceMemory/deviceMemory=] getter steps are to return the [=user agent=]'s [=deviceMemory=]. ## JavaScript examples ## {#javascript-examples} @@ -156,13 +156,13 @@ The `deviceMemory` getter steps are to return [=this=]'s [=deviceMemory=] # Security & privacy considerations # {#security-and-privacy} -`Sec-CH-Device-Memory` Client Hint header and JavaScript API will only be available to HTTPS secure contexts. +[:Sec-CH-Device-Memory:] Client Hint header and JavaScript API will only be available to HTTPS secure contexts. To reduce fingerprinting risk, the reported value is rounded to a single significant bit, as opposed to reporting the exact value. In addition, an implementation-specific upper and lower bound is placed on the reported values. These bounds should be reviewed over time as commonly used device memory characteristics change. Device type should be taken into account when defining these bounds since mobile devices typically have different characteristics than desktops and laptops. # IANA considerations # {#iana} -This document defines the `Sec-CH-Device-Memory` HTTP request header field, and registers them in the permanent message header field registry ([[RFC3864]]). +This document defines the [:Sec-CH-Device-Memory:] HTTP request header field, and registers them in the permanent message header field registry ([[RFC3864]]). ## `Sec-CH-Device-Memory` header field ## {#iana-device-memory} From aebf68d2b205c313aae5ecf83e915e8873829e24 Mon Sep 17 00:00:00 2001 From: Barry Pollard Date: Tue, 10 Mar 2026 18:27:05 +0000 Subject: [PATCH 5/6] Apply suggestion from @tunetheweb --- index.bs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/index.bs b/index.bs index 2cf4705..dfb5f89 100644 --- a/index.bs +++ b/index.bs @@ -81,7 +81,7 @@ The ABNF (Augmented Backus-Naur Form) syntax for the [:Sec-CH-Device-Memory:] he Sec-CH-Device-Memory = sf-decimal ``` -The [:Sec-CH-Device-Memory:]'s value [=user agent=]'s [=deviceMemory=]. +The [:Sec-CH-Device-Memory:]'s value should be set to the [=user agent=]'s [=deviceMemory=]. ## Client Hint examples ## {#client-hint-examples} From 214528c510258c03c4853cadd2799068937ccafe Mon Sep 17 00:00:00 2001 From: Barry Pollard Date: Tue, 10 Mar 2026 18:28:12 +0000 Subject: [PATCH 6/6] Fix algo --- index.bs | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/index.bs b/index.bs index 2cf4705..3908a80 100644 --- a/index.bs +++ b/index.bs @@ -51,19 +51,18 @@ This specification defines a [(Client Hint) Header Field](#sec-device-memory-cli 1. Let |physicalDeviceMemory| be the amount of physical memory in bytes. 2. Let |minimumLowerBound| be an [=implementation-defined=] minimum bound. 3. Let |maximumUpperBound| be an [=implementation-defined=] maximum bound. - 4. Let |deviceMemory| be |physicalDeviceMemory|. + 4. Let |deviceMemory| be |physicalDeviceMemory| / 1024.0. 5. Let |power| be 0. - 6. [=iteration/While=] |deviceMemory| is greater than 0: + 6. [=iteration/While=] |deviceMemory| is greater than 1: 1. Bitwise shift |deviceMemory| right 1 place. 2. Increment |power| by 1. 7. Let |lowerBound| be 2 to the power of |power|. 8. Let |upperBound| be 2 to the power of |power + 1|. 9. If |physicalDeviceMemory| − |lowerBound| ≤ |upperBound| − |physicalDeviceMemory|, then |deviceMemory|'s value is |lowerBound|. 10. Otherwise |deviceMemory|'s value is |upperBound|. - 11. |deviceMemory| is |deviceMemory| / 1024.0. - 12. If |deviceMemory| < |minimumLowerBound|, then |deviceMemory| is |minimumLowerBound|. - 13. If |deviceMemory| > |maximumUpperBound|, then |deviceMemory| is |maximumUpperBound|. - 14. Return |deviceMemory|. + 11. If |deviceMemory| < |minimumLowerBound|, then |deviceMemory| is |minimumLowerBound|. + 12. If |deviceMemory| > |maximumUpperBound|, then |deviceMemory| is |maximumUpperBound|. + 13. Return |deviceMemory|.
The algorithm includes the ability for [=implementation-defined=] upper bound and a lower bounds. The range between the upper and the lower bounds should include the majority of device memory values but exclude rare device memory values to mitigate device fingerprinting. Implementations may adjust these bounds over time. These bounds may differ on different device types. @@ -81,7 +80,7 @@ The ABNF (Augmented Backus-Naur Form) syntax for the [:Sec-CH-Device-Memory:] he Sec-CH-Device-Memory = sf-decimal ``` -The [:Sec-CH-Device-Memory:]'s value [=user agent=]'s [=deviceMemory=]. +The [:Sec-CH-Device-Memory:]'s value should be set to the [=user agent=]'s [=deviceMemory=]. ## Client Hint examples ## {#client-hint-examples}