ModHeaders

A Chrome extension that lives in the side panel and lets you configure HTTP request/response header rules with a polished, distraction-free UI.

Built on Chrome's modern declarativeNetRequest API (Manifest V3).

Features

• Side panel UX — open from any tab, stays out of your way
• Per-rule header set / append / remove for both request and response
• URL, domain, or regex matching
• Per-resource-type filters (XHR, main_frame, script, …)
• Master toggle to instantly pause every rule
• Search, duplicate, import / export JSON
• Light + dark theme (follows system)
• Keyboard: / focus search · ⌘N new rule · ⌘S save · Esc back

Browser support

Browser	Side panel	DNR rules	Status
Chrome ≥116	yes	yes	full
Edge ≥116	yes	yes	full
Brave ≥1.58	yes	yes	full
Opera ≥102	yes	yes	full
Arc	yes	yes	full
Vivaldi ≥6.4	yes	yes	full
Chromium ≥116	yes	yes	full
Firefox	no (1)	partial	load as temp add-on

(1) Firefox does not implement the side panel API. Use about:debugging to load.

Quick start

1. Open the side panel by clicking the ModHeaders toolbar icon.
2. Click + New Rule (or press ⌘N / Ctrl+N).
3. Give it a name, set a URL pattern (e.g. *://api.example.com/*).
4. Add headers — choose request or response, pick set/append/remove.
5. Click Save (⌘S / Ctrl+S). Headers inject immediately.
6. Toggle the master switch to pause/resume all rules at once.

Import/export your rule set as JSON from the ⋮ menu.

Install

One-liner

# macOS / Linux
curl -fsSL https://raw.githubusercontent.com/4nkitd/mod-headers/main/tools/install.sh | bash

# macOS / Linux — temporary load (gone after browser quits)
curl -fsSL https://raw.githubusercontent.com/4nkitd/mod-headers/main/tools/install.sh | bash -s -- --load-temp

# Windows PowerShell
iex "& { $(irm https://raw.githubusercontent.com/4nkitd/mod-headers/main/tools/install.ps1) }"

:: Windows CMD — opens browser extension pages (requires Git Bash)
curl -fsSL https://raw.githubusercontent.com/4nkitd/mod-headers/main/tools/install.sh | bash

From local checkout

bash tools/install.sh
# or temp load:
bash tools/install.sh --load-temp

Detects your OS and installed browsers (Chrome, Edge, Brave, Opera, Arc, Vivaldi, Chromium, Firefox, Firefox Dev) — opens each to the right page and prints instructions. When piped via curl the script clones the repo automatically.

Manual (unpacked)

1. Open chrome://extensions
2. Toggle Developer mode on (top right)
3. Click Load unpacked and choose this folder
4. Pin the extension and click its toolbar icon to open the side panel

Project layout

manifest.json
icons/                        generated PNGs
src/
  background/service-worker.js   syncs storage → DNR dynamic rules
  lib/storage.js                 chrome.storage facade
  lib/rules.js                   rule shape + DNR translation
  sidepanel/                     UI (HTML / CSS / JS)
tools/make-icons.py              regenerate icons (uv run …)
tools/install.sh                  cross-browser auto-installer
tools/test-ui.mjs                 visual smoke test (Playwright)

Regenerating icons

uv run tools/make-icons.py

How rules become DNR rules

Storage holds a plain rules[] array. The service worker watches chrome.storage and rebuilds the dynamic DNR ruleset on every change:

• enabled rules with at least one valid header op are emitted
• match type translates to urlFilter / requestDomains / regexFilter
• resource-type filter is applied if specified, otherwise all types

When the master toggle is off, the dynamic ruleset is simply emptied — no rules fire until you flip it back on.