Modifly
Getting started

Custom request headers, without changing your code.

Modifly adds the headers you choose to requests for specific websites. Use it for local development, staging environments, feature flags, or API testing.

Create your first rule
Local only Rules stay in this Chrome profile.
Per-site access You approve each configured hostname.
Under your control Pause, edit, or delete a rule at any time.
01

Quick start

Create your first rule

  1. 1

    Open the website

    Visit the website where the header should be applied, then open Modifly from the Chrome toolbar. The hostname is filled in automatically when possible.

  2. 2

    Enter the rule

    Hostname api.example.com
    Header name X-Debug
    Header value enabled

    Enter a bare hostname without https://, a port, or a path. You can separate multiple hostnames with commas.

  3. 3

    Add the rule and allow access

    Select Add rule. Chrome asks whether Modifly may access the configured site. Choose Allow to activate the rule.

  4. 4

    Reload and test

    Reload the target website so it makes new network requests. Your enabled rule is applied automatically to matching requests.

02

Everyday use

Manage your rules

Pause or resume

Use the switch beside a rule to disable it temporarily without deleting its settings.

Edit

Select the pencil icon, change the hostname, header name, or value, then save your changes.

Delete

Select the trash icon to permanently remove a rule from this Chrome profile.

Restore site access

If a rule says Permission required, select Grant and approve access in Chrome.

03

Use credentials carefully

Privacy and security

What stays on your device

Hostnames, header names, and header values are stored locally in your Chrome profile. Modifly does not sync them or send them to the extension publisher.

What you should avoid

Chrome extension storage is not encrypted. Avoid long-lived production tokens and revoke any credential that may have been exposed.

04

Troubleshooting

Common questions

The rule says “Permission required.”

Select Grant beside the rule and approve the Chrome access prompt. If the prompt does not appear, open chrome://extensions, select Modifly, and review its site access.

The header does not appear on my request.

Confirm that the rule is enabled, access is granted, and the destination hostname matches the rule. Reload the page to create a new request. Modifly intentionally does not attach a rule to requests initiated by unrelated websites.

Which hostname format should I use?

Use only the hostname, such as api.example.com. Do not include a protocol, port, path, query, or fragment.

Why did the popup close after I selected Add rule?

Chrome can close extension popups while showing a site-access prompt. Your draft is preserved. After approving or declining access, reopen Modifly to continue.

Does Modifly read or upload page content?

No. It uses Chrome's request-rule system to set the headers you configure. It does not read page responses or upload your rules to an external service.