declarativeNetRequest response-header modifications are not shown in DevTools (Manifest V3)

[Orest Kreminsky]

Hi,

I found the existing Chromium issue 40196848, which appears to describe this behavior. The issue was reported several years ago and currently appears to remain open.

Could someone confirm whether this issue still tracks the current DevTools behavior and whether there are any plans to address it?

We are developing a Manifest V3 header override extension that modifies request and response headers using chrome.declarativeNetRequest.

The dynamic rules are registered using:

const existingRules = await chrome.declarativeNetRequest.getDynamicRules(); await chrome.declarativeNetRequest.updateDynamicRules({ removeRuleIds: existingRules.map(rule => rule.id) }); await chrome.declarativeNetRequest.updateDynamicRules({ addRules: [rule] });

The rule is registered successfully, and the modified header is visible to JavaScript:

const response = await fetch("/some-resource"); console.log( response.headers.get("x-debug-mode") ); // "on"

However, the header does not appear under:

DevTools → Network → Headers → Response Headers

Could you please clarify:

1. Is Chromium issue 40196848 still the correct issue for this behavior?
2. Are there plans for DevTools to display headers added, changed, or removed by extensions?

Thank you.

[Anton Bershanskyi]

Hi Orest,

> Is Chromium issue 40196848 still the correct issue for this behavior?

Yes, you correctly identified this bug and issue number in Chromium bug tracker.

> Are there plans for DevTools to display headers added, changed, or removed by extensions?

In short: As you can see on the issue tracker, patches are welcome, but the core team does not have time to work on this. (Bug was reported in 2021, latest human comment is from April of 2023 and it it one developer asks if this work can be put on schedule to "pick up the work from Joey and land that during the year".)

I am not a Google employee, I'm just an outside contributor with a few patches upstreamed to Chromium project, so the following is based only on my experience. This is a fairly fundamental bug and fix requires a substantial amount of work across multiple repositories (chromium and devtools-frontend). I personally encountered this bug before and worked around it by disabling extensions and logging interesting headers to the console. The latest public comment was in 2023 and there had been no interest in this bug since. It is not very likely that someone will pick this bug to work on, unfortunately.

Sincerely,

Anton.