URL Query Parameter Appender

URL Query Parameter Appender is a practical and efficient browser extension designed to automate the process of adding custom query parameters to URLs based on specified hostnames. This tool is especially useful for developers, marketers, testers, and power users who need to consistently apply parameters such as tracking codes, analytics tags, affiliate identifiers, or feature flags across multiple browsing sessions without manually editing URLs. By seamlessly integrating into your browsing experience, the extension ensures that every visit to specified domains automatically includes your defined query parameters, eliminating errors and saving time.

The user interface is accessible via a compact, streamlined popup inspired by popular tools like ModHeader. You can easily create and manage mappings between hostnames and their appending query parameters. Simply click "+ Add mapping" at the bottom of the list, enter a hostname (for example "example.com") along with query parameters like "utm_source=extension&utm_campaign=promo," and your mapping is saved instantly. Input validation is built in to verify hostnames and parameter strings, providing immediate feedback to prevent mistakes.

All your mappings are displayed in a clean, space-efficient list where each entry can be edited inline—just click on the hostname, parameters, or comment field to modify them, and changes are auto-saved as you type. Each mapping includes a checkbox to quickly enable or disable it without deleting, perfect for temporarily turning off certain parameters while keeping your configuration intact. Add optional comments to document what each mapping is used for, making it easy to remember the purpose of each configuration. Removing a mapping is just one click away with the delete button.

A powerful feature is the ability to create multiple mappings for the same hostname. This allows you to organize different parameter sets separately—for example, one mapping for analytics tracking and another for A/B testing—and enable or disable them independently. When multiple mappings for the same hostname are enabled, their parameters are automatically merged. If the same parameter key appears in multiple enabled mappings, the value from the mapping added later in the list takes precedence. Entries that share a hostname with other entries are visually indicated with a colored border, making it easy to identify related configurations at a glance.

Leveraging the declarativeNetRequest API, the extension performs its URL modifications quickly, securely, and at a network-request level inside the browser. This means URLs are altered before navigation happens, making the process robust and reliable even under complex browsing conditions. Further enhancing usability, your settings are stored in the browser's sync storage, enabling automatic synchronization across your devices and profiles where you are signed in and have extension sync enabled in your browser settings.

The extension has been developed with privacy as a foremost concern. It does not collect or inspect any personal browsing data, cookies, or page content. All data related to query parameter mappings remain on your device or within your browser sync account, giving you full control and transparency.