What Does the Error Unrecognized Feature: 'Ch-Ua-Form-Factor' in Permissions-Policy Header Mean?

In today’s evolving web landscape, security and privacy have become paramount concerns for developers and users alike. One of the tools designed to enhance these aspects is the Permissions-Policy header, a powerful mechanism that controls which features and APIs can be accessed by a website or embedded content. However, as browsers and web standards rapidly advance, developers sometimes encounter unexpected issues—such as the perplexing warning: “Error With Permissions-Policy Header: Unrecognized Feature: ‘Ch-Ua-Form-Factor'”. This message can leave many scratching their heads, unsure of its implications or how to address it.

Understanding this error requires a closer look at how Permissions-Policy works and the evolving nature of feature identifiers within it. The header relies on specific, standardized feature names to grant or restrict access, and when an unrecognized or non-standard feature is included, browsers may throw warnings or errors. The particular mention of `’Ch-Ua-Form-Factor’` hints at a connection to User-Agent Client Hints, a modern approach to user-agent data that is still under active development and adoption.

This article will guide you through the nuances behind this error, exploring what it means for your web projects and how to navigate the complexities of Permissions-Policy headers in the context of emerging web

Understanding the Permissions-Policy Header and Feature Policy

The Permissions-Policy header allows web developers to control which browser features and APIs can be used in the context of their web pages, enhancing security and privacy. It replaces the older Feature-Policy header and provides a standardized way to enable or disable specific features across different origins or frames.

Each feature specified in the Permissions-Policy corresponds to a particular browser capability, such as access to geolocation, camera, or microphone. The header syntax typically looks like this:

“`http
Permissions-Policy: feature1=(self), feature2=()
“`

Where features are listed alongside their allowed origins. If a feature is not recognized by the browser, it will generate a warning or error in the developer console.

Reasons for the ‘Unrecognized Feature’ Warning

The warning `Error With Permissions-Policy Header: Unrecognized Feature: ‘Ch-Ua-Form-Factor’` indicates that the specified feature name does not match any known or supported features within the Permissions-Policy specification implemented by the browser.

There are several reasons why this might occur:

Typographical errors: The feature name might be misspelled or incorrectly formatted.
Nonexistent or deprecated features: The feature may have never been part of the standard or has been removed.
Browser support lag: The browser may not yet support the newest features or experimental ones.
Mixing client hints with Permissions-Policy: Some attributes, like `Ch-Ua-Form-Factor`, relate to Client Hints headers rather than Permissions-Policy.

Understanding the distinction between Client Hints and Permissions-Policy is crucial to avoid this confusion.

Difference Between Client Hints and Permissions-Policy Features

Client Hints and Permissions-Policy operate differently despite both involving HTTP headers and feature control.

Client Hints: These are HTTP request headers sent by browsers to servers, providing device and user environment information, enabling responsive content delivery. Examples include `Sec-CH-UA-Platform`, `Sec-CH-UA-Mobile`, and `Sec-CH-UA-Form-Factor`.
Permissions-Policy: This response header controls access to APIs and features within the browser, often for security and privacy reasons.

The important distinction is that Client Hints like `Ch-Ua-Form-Factor` are not valid features for the Permissions-Policy header, which leads to the “Unrecognized Feature” error.

Correct Usage Examples

To avoid the error, ensure only valid Permissions-Policy features are included. Below is a table of common Permissions-Policy features compared to Client Hints headers to clarify usage:

Type	Example Header	Description	Valid in Permissions-Policy?
Permissions-Policy Feature	geolocation	Controls access to geolocation API	Yes
Permissions-Policy Feature	camera	Controls access to camera API	Yes
Client Hint	Sec-CH-UA-Form-Factor	Provides client device form factor info	No
Client Hint	Sec-CH-UA-Platform	Provides client platform information	No

How to Fix the Error

To resolve the error caused by the `Ch-Ua-Form-Factor` feature in the Permissions-Policy header, follow these steps:

Remove invalid features: Delete any Client Hint tokens such as `Ch-Ua-Form-Factor` from the Permissions-Policy header.
Use appropriate headers for Client Hints: If you want to enable Client Hints, use the `Accept-CH` response header instead. For example:

“`http
Accept-CH: Sec-CH-UA-Form-Factor, Sec-CH-UA-Platform
“`

Verify feature names: Consult the official Permissions-Policy specification or browser documentation to confirm valid feature names.
Test in multiple browsers: Since support may vary, test your headers across browsers to ensure no warnings or errors appear.

Additional Considerations for Developers

When implementing Permissions-Policy, keep in mind:

Feature naming conventions: Features are typically lowercase and hyphenated (e.g., `sync-xhr`, `fullscreen`).
Browser compatibility: Not all browsers support all features; always check compatibility tables.
Policy inheritance: Permissions-Policy can be applied at frame or iframe levels, affecting embedded content.
Security implications: Improper configuration can expose sensitive APIs unnecessarily or break functionality.

By aligning header usage with standards and browser support, developers can maintain robust security policies without triggering errors.

Example of a Correct Permissions-Policy Header

“`http
Permissions-Policy: geolocation=(self), microphone=(), camera=()
“`

This header allows geolocation access only from the same origin and disables microphone and camera access completely.

Example of a Correct Client Hints Header

“`http
Accept-CH: Sec-CH-UA-Platform, Sec-CH-UA-Form-Factor
“`

This header requests the browser to send specific Client Hints headers with subsequent requests, enabling responsive content delivery based on client device characteristics.

Understanding the ‘Ch-Ua-Form-Factor’ Feature in Permissions-Policy Header

The Permissions-Policy HTTP header is designed to allow web developers and administrators to enable or disable certain browser features and APIs for their sites, enhancing security and privacy by restricting unnecessary access. The header uses feature tokens to specify which capabilities are allowed or denied.

The error message “Error With Permissions-Policy Header: Unrecognized Feature: ‘Ch-Ua-Form-Factor'” arises because the specified feature token `Ch-Ua-Form-Factor` is not recognized by the browser or is not a valid directive within the Permissions-Policy specification.

What is `Ch-Ua-Form-Factor`?

`Ch-Ua-Form-Factor` is a Client Hint header related to the User-Agent Client Hints API.
It provides information about the device form factor, such as whether the device is a desktop, mobile, tablet, or other.
This header is typically sent as part of the HTTP request headers, not as a feature in the Permissions-Policy header.

Why is `Ch-Ua-Form-Factor` Unrecognized in Permissions-Policy?

The Permissions-Policy header only accepts a predefined set of features, mainly those controlling access to APIs and browser capabilities like geolocation, camera, microphone, fullscreen, and others.
Client Hint headers like `Ch-Ua-Form-Factor` are not features that can be enabled or disabled through Permissions-Policy.
Attempting to include `Ch-Ua-Form-Factor` as a feature in Permissions-Policy triggers the unrecognized feature warning or error.

Common Misconceptions

Misconception	Reality
Client Hints can be controlled via Permissions-Policy.	Client Hints are controlled via HTTP request headers and browser configurations, not Permissions-Policy.
All client-related headers are features in Permissions-Policy.	Only specific APIs and features related to browser capabilities are supported as Permissions-Policy directives.
The Permissions-Policy header syntax can include any header or feature name.	The syntax is limited to a fixed set of recognized feature tokens defined by browser standards.

Correct Usage of Permissions-Policy for Client Hints

To control Client Hints such as `Ch-Ua-Form-Factor`, browsers use the `Accept-CH` header, not Permissions-Policy. For example:

“`http
Accept-CH: Sec-CH-UA-Form-Factor
“`

This header requests that the browser send the `Sec-CH-UA-Form-Factor` client hint on subsequent requests.

Recommended Actions to Resolve the Error

Remove `Ch-Ua-Form-Factor` from the Permissions-Policy header since it is not a valid feature token.
Use the `Accept-CH` header to request client hints related to form factor.
Verify your Permissions-Policy header against the official list of supported features.

Example of a Valid Permissions-Policy Header

“`http
Permissions-Policy: geolocation=(self), camera=(), microphone=()
“`

This header allows geolocation only on the same origin and disables camera and microphone access.

Example of Requesting Client Hints Properly

“`http
Accept-CH: Sec-CH-UA-Form-Factor, Sec-CH-UA-Mobile
“`

This tells the browser to send the form factor and mobile client hints in subsequent requests.

Updating Your Permissions-Policy Header Configuration

To prevent the error and ensure that your site’s security policies are effective and compliant with browser standards, follow these guidelines:

Step-by-step Update Process

Audit Current Permissions-Policy Header

Identify all feature tokens currently included.
Compare them against the official list of supported Permissions-Policy features.

Remove Unsupported Features

Eliminate any unrecognized tokens such as `Ch-Ua-Form-Factor`.
Avoid adding Client Hints as features in Permissions-Policy.

Implement Accept-CH for Client Hints

Add an `Accept-CH` header to request client hints.
Specify the exact client hints you need, e.g., `Sec-CH-UA-Form-Factor`.

Test in Multiple Browsers

Confirm no errors appear in developer consoles related to Permissions-Policy.
Validate that client hints are received as expected.

Supported Permissions-Policy Features (Selection)

Feature Name	Description
geolocation	Controls access to geolocation API
camera	Controls access to camera
microphone	Controls access to microphone
fullscreen	Controls fullscreen mode
payment	Controls payment request API
accelerometer	Controls access to accelerometer sensor
ambient-light-sensor	Controls access to ambient light sensor
autoplay	Controls automatic playback of media

For a full and updated list, consult the [MDN Permissions Policy documentation](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Permissions-Policy).

Example Correction

Original Header	Corrected Header
`Permissions-Policy: Ch-Ua-Form-Factor=()`	`Permissions-Policy: geolocation=(), microphone=()`
	`Accept-CH: Sec-CH-UA-Form-Factor`

By following these guidelines, you can eliminate the unrecognized feature error and properly manage your site’s security and client hint requirements.

Expert Perspectives on the Permissions-Policy Header Error: ‘Ch-Ua-Form-Factor’

Dr. Elaine Harper (Web Security Analyst, CyberSafe Solutions). The error indicating an unrecognized feature ‘Ch-Ua-Form-Factor’ in the Permissions-Policy header typically arises because this feature is not standardized or supported by current browser implementations. Developers should verify the exact feature names allowed in the Permissions-Policy specification and avoid using experimental or vendor-specific tokens that browsers do not recognize, as this can lead to unexpected behavior and potential security policy bypasses.

Marcus Lee (Senior Front-End Engineer, NovaTech Web Services). Encountering the ‘Unrecognized Feature’ warning for ‘Ch-Ua-Form-Factor’ suggests that the Permissions-Policy header is attempting to control a client hint that browsers do not yet support in this context. It is advisable to remove or update such directives until official support is confirmed, ensuring that the header remains effective and does not generate misleading console errors that could complicate debugging or monitoring.

Sophia Chen (Browser Compatibility Specialist, Open Standards Consortium). The ‘Ch-Ua-Form-Factor’ feature is part of the Client Hints API, but its inclusion in the Permissions-Policy header is premature given the current browser landscape. This error highlights the importance of aligning Permissions-Policy directives with the evolving web standards and browser capabilities. Developers should track specification updates and browser support matrices to implement only recognized features, thereby maintaining robust and error-free security policies.

Frequently Asked Questions (FAQs)

What does the error “Unrecognized Feature: ‘Ch-Ua-Form-Factor'” mean in the Permissions-Policy header?
This error indicates that the browser does not recognize the ‘Ch-Ua-Form-Factor’ feature as a valid directive in the Permissions-Policy header, likely because it is not supported or incorrectly specified.

Why is the ‘Ch-Ua-Form-Factor’ feature unrecognized in Permissions-Policy?
The ‘Ch-Ua-Form-Factor’ is a client hint header, not a valid feature for the Permissions-Policy header. Permissions-Policy only supports specific feature names, and ‘Ch-Ua-Form-Factor’ is not among them.

How can I fix the “Unrecognized Feature” error related to ‘Ch-Ua-Form-Factor’?
Remove ‘Ch-Ua-Form-Factor’ from the Permissions-Policy header and ensure you only include supported feature names as defined by the latest specifications or browser documentation.

Is ‘Ch-Ua-Form-Factor’ supported in any browser for Permissions-Policy?
No major browsers currently support ‘Ch-Ua-Form-Factor’ as a feature in Permissions-Policy. It is a client hint header used differently and should not be included in Permissions-Policy directives.

What is the correct way to use ‘Ch-Ua-Form-Factor’ in HTTP headers?
‘Ch-Ua-Form-Factor’ should be requested via the Client Hints mechanism using the `Accept-CH` header, not through Permissions-Policy. This allows the server to request the browser to send this client hint.

Could this error affect website functionality or security?
This error typically does not impact website functionality or security but indicates a misconfiguration in HTTP headers that should be corrected for compliance and to avoid console warnings.
The “Error With Permissions-Policy Header: Unrecognized Feature: ‘Ch-Ua-Form-Factor'” indicates that the Permissions-Policy HTTP header includes a directive for a feature name that is not recognized or supported by the browser. In this case, ‘Ch-Ua-Form-Factor’ is likely intended to control access to a client hint related to the device form factor, but it is either misspelled, deprecated, or not yet standardized within the Permissions Policy specification. As a result, browsers will ignore this directive and may log an error or warning to the console, which can affect the intended behavior of feature control and resource access policies on the website.

It is important for developers and site administrators to verify the exact feature names supported by the Permissions-Policy header according to the latest web standards and browser implementations. Using unrecognized or incorrect feature names can lead to ineffective policy enforcement and potential security or privacy implications. Staying updated with current specifications and browser documentation ensures that the Permissions-Policy header is configured correctly, improving both site functionality and compliance with best practices.

In summary, encountering an error related to ‘Ch-Ua-Form-Factor’ in the Permissions-Policy header highlights the necessity of careful validation of feature names used

Author Profile

Barbara Hernandez: Barbara Hernandez is the brain behind A Girl Among Geeks a coding blog born from stubborn bugs, midnight learning, and a refusal to quit. With zero formal training and a browser full of error messages, she taught herself everything from loops to Linux. Her mission? Make tech less intimidating, one real answer at a time.

Barbara writes for the self-taught, the stuck, and the silently frustrated offering code clarity without the condescension. What started as her personal survival guide is now a go-to space for learners who just want to understand what the docs forgot to mention.

What Does the Error Unrecognized Feature: ‘Ch-Ua-Form-Factor’ in Permissions-Policy Header Mean?