Header Modifier

Chrome extension that allows you to modify HTTP headers for specific URLs and apply rules based on the current page you're visiting.

# Header Modifier ## Description **Header Modifier** is a powerful Chrome extension that allows you to modify HTTP request headers for specific URLs and apply rules based on the current page you're visiting. Perfect for developers, testers, and power users who need to customize request headers for API testing, authentication, user-agent spoofing, or debugging web applications. ### Key Features: - **Global Plugin Toggle**: Instantly enable or disable the entire extension with a single switch at the top of the popup — your rules stay saved - **Smart Page-Based Rules**: Apply header modifications only when visiting specific websites - **Global or Contextual**: Create rules that work globally or only on specific pages - **Header Modification**: Add, modify, or override any HTTP request header using a simple key-value editor — no JSON required - **URL Redirection**: Redirect specific requests to different URLs - **Per-Rule Toggle**: Enable or disable individual rules without deleting them - **Per-Header Toggle**: Enable or disable individual headers within a rule independently - **Grouped Rule List**: Rules are grouped by page pattern with an expandable detail view to inspect header values - **Filter / Search**: Quickly find rules by URL pattern, page pattern, or header name/value - **Smart Suggestions**: Autocomplete for page patterns, request URL patterns, common header names, and header values - **Use Current URL**: Pre-fill both patterns from the active browser tab with one click - **Real-time Updates**: Rules activate atomically when switching tabs or navigating — no gap where requests go unmodified - **Import / Export**: Backup, share, or migrate your rule configurations as JSON files --- ## How to Use ### 1. Turning the Plugin On / Off The **ON/OFF toggle** in the top-right corner of the popup controls the entire extension. When set to **OFF**, all declarativeNetRequest rules are removed immediately — no requests are modified. When turned back **ON**, all your saved rules are reapplied. Individual rule states are preserved. --- ### 2. Creating Rules 1. Click the extension icon in your toolbar 2. In the **Add Rule** section at the bottom of the popup, fill in: - **Page Pattern** *(optional)*: The page URL where this rule should be active (e.g., `*://example.com/*`). Leave empty for a global rule that is always active. - **Request URL Pattern**: Which outgoing requests to intercept (e.g., `*://api.example.com/*`) - **Action**: Choose **Modify Headers** or **Redirect** 3. Click **Use Current URL** to auto-fill both patterns from the active tab 4. Click **Add Rule** #### For Header Modification: Use the key-value row editor to add headers: - Click **+ Add Header** to add a new row - Type the header name (autocomplete suggestions are provided for common headers) - Type the header value (context-aware suggestions appear based on the header name) - Add as many headers as needed #### For URL Redirection: Enter the full destination URL in the **Redirect URL** field. --- ### 3. URL Pattern Examples #### Page Patterns (when to apply the rule): | Pattern | Matches | |---|---| | `*://example.com/*` | Only on example.com | | `*://localhost:3000/*` | Only on localhost port 3000 | | `*://*.google.com/*` | All Google subdomains | | *(empty)* | Global — applies on every page | #### Request URL Patterns (which requests to modify): | Pattern | Matches | |---|---| | `*://api.example.com/*` | All requests to api.example.com | | `*://*/api/v1/*` | API v1 endpoints on any domain | | `https://cdn.example.com/*` | Only HTTPS CDN requests | --- ### 4. Common Use Cases #### API Authentication: ``` Page Pattern: *://myapp.com/* Request Pattern: *://api.myapp.com/* Headers: Authorization → Bearer abc123 ``` #### Redirect Dev Traffic to Local Server: ``` Page Pattern: *://localhost:3000/* Request Pattern: *://api.production.com/* Action: Redirect to http://localhost:8080/api/ ``` #### User-Agent Override (global): ``` Page Pattern: (empty — global) Request Pattern: *://*/* Headers: User-Agent → Custom Browser 2.0 ``` --- ### 5. Managing Rules #### Rules List: - Rules are **grouped by page pattern** (Global rules appear first) - Click **▼** next to a rule to expand and see its header key-value pairs - Each rule shows an **ON/OFF** toggle and a **×** delete button - Each individual header row also has its own **ON/OFF** toggle and **×** delete button - Use the **Filter** input at the top of the list to search by URL, page pattern, header name, or header value #### Enable / Disable: - **Plugin toggle** (top of popup): turns the entire extension on or off - **Rule toggle**: enables or disables a single rule - **Header toggle**: enables or disables one header within a rule, without affecting others #### Import / Export: - Click **↓ Export** to download all rules as a JSON file - Click **↑ Import** to load rules from a JSON file — choose **Merge** (add to existing) or **Replace All** --- ### 6. Tips & Best Practices 1. **Leave Page Pattern empty for rules you always need** — global rules are always active regardless of the current tab 2. **Use specific patterns** — overly broad patterns like `*://*/*` intercept every request and can slow things down 3. **Disable instead of delete** — use the toggle to temporarily turn off a rule while keeping its configuration 4. **Check the active count** — the context bar shows how many rules are active for the current page 5. **Page vs Request pattern**: - *Page pattern* = what website you must be on for the rule to activate - *Request pattern* = which outgoing requests actually get modified --- ### 7. Security Note This extension modifies HTTP request headers which can affect website security. Use responsibly: - Do not expose sensitive tokens in shared rule exports - Use specific page patterns to avoid unintended header injection - Test rules in a development environment before deploying to production - Review and clean up unused rules periodically --- ### 8. Troubleshooting #### Headers not being applied? 1. Check the **plugin toggle** — ensure it is set to **ON** 2. Check the **rule toggle** — ensure the specific rule is enabled 3. Verify the **Request URL Pattern** matches the actual request URL (you can inspect this in DevTools → Network) 4. Open the background service worker console (chrome://extensions → Header Modifier → "Service Worker") and check for errors 5. Reload the extension from **chrome://extensions** after any manual file changes #### Rules not showing in the popup? 1. Reload the extension from **chrome://extensions** 2. Reopen the popup #### Pattern tips: - `*://` matches both `http://` and `https://` - `*://localhost:3000/*` correctly includes the port number - A missing trailing `/*` means the pattern only matches the exact URL, not sub-paths