HeaderInject

Inject custom HTTP headers into web requests before interacting with pages. HeaderInject is built for testing, development, and authentication workflows that need precise header control. HeaderInject - Custom Headers Made Simple Add, edit, and manage HTTP request headers from a clean popup UI, then apply them instantly to matching sites - globally or per-header. Key Features: - One-click enable/disable toggle - Global URL pattern targeting (leave blank to apply everywhere) - Per-header domain scoping: assign one or more domains to a header (e.g. a different API key per environment) - headers without domains follow the global pattern - Add, edit, and delete multiple headers - Prevents duplicate header names - Save and apply changes in one action - Light and dark theme - Works across most request types (pages, XHR, fetch, media, etc.) - Local-only settings stored in the browser How It Works: 1. Open the extension popup 2. (Optional) Enter a global URL pattern like *://api.example.com/* 3. Add one or more headers (name + value) 4. (Optional) Scope a header to specific domains like api.example.com, staging.example.com 5. Click "Save & Apply" 6. Reload the page so the rules take effect Perfect For: - Testing APIs that require custom authentication headers or flags - Using different API keys for different domains or environments at the same time - Debugging staging environments with feature flags - Injecting tenant, locale, or environment headers - Quickly switching between header sets during development Privacy First: - No servers involved - Settings are stored locally - No data collection Tips: - If a header does not appear, the browser may restrict certain headers from being modified. - Reload the page after saving to ensure changes apply. - Leave a header's Domains field empty to let it follow the global URL pattern.