Renders Cursor Rules (*.mdc) markdown on GitHub into actual Markdown locally, using the marked library + highlight.js.
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// ==UserScript==
// @name Cursor Rule Markdown Renderer for GitHub
// @namespace https://github.com/texarkanine
// @version 2025-05-27
// @description Renders Cursor Rules (*.mdc) markdown on GitHub into actual Markdown locally, using the marked library + highlight.js.
// @author Texarkanine
// @match https://github.com/*
// @icon data:image/png;base64,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
// @grant GM_addStyle
// @require https://cdnjs.cloudflare.com/ajax/libs/marked/15.0.7/marked.min.js
// @require https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.11.1/highlight.min.js
// ==/UserScript==
(function() {
'use strict';
const DEBUG = true;
const MDC_FILE_REGEX = /^https:\/\/github\.com\/.*\.mdc$/;
const YAML_FRONTMATTER_REGEX = /^---\s*\n([\s\S]*?)\n---\s*\n([\s\S]*)$/;
const RENDERED_LABEL = 'MD🠯';
const SOURCE_LABEL = '.mdc';
const MAX_RENDER_ATTEMPTS = 50;
const RENDER_RETRY_INTERVAL = 100;
let currentUrl = location.href;
let isActive = false;
let textareaObserver = null;
GM_addStyle(`
.markdown-body {
box-sizing: border-box;
min-width: 200px;
max-width: 980px;
margin: 24px auto 0;
padding: 45px;
word-wrap: break-word;
}
`);
/**
* Processes MDC content by extracting YAML frontmatter and converting it to a code block
* @param {string} content - Raw MDC file content
* @returns {string} Processed content with YAML frontmatter as code block
*/
function processContent(content) {
const match = content.match(YAML_FRONTMATTER_REGEX);
if (match) {
const [, yamlContent, markdownContent] = match;
return `\`\`\`yaml\n${yamlContent}\n\`\`\`\n\n${markdownContent}`;
}
return content;
}
/**
* Creates a button element with GitHub's styling
* @param {string} label - Button text content
* @param {string} mode - View mode ('rendered' or 'source')
* @param {boolean} isSelected - Whether button should be in selected state
* @returns {HTMLLIElement} Complete button list item element
*/
function createButton(label, mode, isSelected = false) {
const li = document.createElement('li');
li.className = `SegmentedControl-item${isSelected ? ' SegmentedControl-item--selected' : ''}`;
li.setAttribute('role', 'listitem');
const button = document.createElement('button');
button.setAttribute('aria-current', isSelected.toString());
button.setAttribute('type', 'button');
button.setAttribute('data-view-component', 'true');
button.className = 'Button--invisible Button--small Button Button--invisible-noVisuals';
button.onclick = () => setViewMode(mode);
const content = document.createElement('span');
content.className = 'Button-content';
const labelSpan = document.createElement('span');
labelSpan.className = 'Button-label';
labelSpan.setAttribute('data-content', label);
labelSpan.textContent = label;
content.appendChild(labelSpan);
button.appendChild(content);
li.appendChild(button);
return li;
}
/**
* Creates a GitHub-styled segmented control for toggling between rendered and source views
* @returns {HTMLDivElement} Complete toggle button control
*/
function createToggleButton() {
const container = document.createElement('div');
container.className = 'mdc-segmented-control';
const segmentedControl = document.createElement('segmented-control');
segmentedControl.setAttribute('data-catalyst', '');
const ul = document.createElement('ul');
ul.setAttribute('aria-label', 'MDC view');
ul.setAttribute('role', 'list');
ul.setAttribute('data-view-component', 'true');
ul.className = 'SegmentedControl--small SegmentedControl';
ul.appendChild(createButton(RENDERED_LABEL, 'rendered', true));
ul.appendChild(createButton(SOURCE_LABEL, 'source', false));
segmentedControl.appendChild(ul);
container.appendChild(segmentedControl);
return container;
}
/**
* Switches between rendered markdown and source code views
* @param {'rendered'|'source'} mode - View mode to activate
*/
function setViewMode(mode) {
const rendered = document.getElementById('mdc-rendered');
const original = document.querySelector('#read-only-cursor-text-area')?.closest('section');
const buttons = document.querySelectorAll('.mdc-segmented-control .SegmentedControl-item');
if (!rendered || !original || buttons.length !== 2) return;
const [renderedItem, sourceItem] = buttons;
const renderedButton = renderedItem.querySelector('button');
const sourceButton = sourceItem.querySelector('button');
const isRenderedMode = mode === 'rendered';
rendered.style.display = isRenderedMode ? 'block' : 'none';
original.style.display = isRenderedMode ? 'none' : 'block';
renderedItem.classList.toggle('SegmentedControl-item--selected', isRenderedMode);
sourceItem.classList.toggle('SegmentedControl-item--selected', !isRenderedMode);
if (renderedButton) renderedButton.setAttribute('aria-current', isRenderedMode.toString());
if (sourceButton) sourceButton.setAttribute('aria-current', (!isRenderedMode).toString());
}
/**
* Renders MDC content as HTML and inserts it into the page
* @returns {boolean} True if rendering was successful, false otherwise
*/
function renderMDC() {
const textarea = document.querySelector('#read-only-cursor-text-area');
if (!textarea) {
DEBUG && console.log('[mdc-lite] No textarea found');
return false;
}
const content = textarea.textContent?.trim();
if (!content) {
DEBUG && console.log('[mdc-lite] No content in textarea');
return false;
}
const existing = document.getElementById('mdc-rendered');
existing?.remove();
const processedContent = processContent(content);
const rendered = document.createElement('div');
rendered.id = 'mdc-rendered';
rendered.className = 'markdown-body';
rendered.innerHTML = marked.parse(processedContent);
rendered.querySelectorAll('pre code').forEach(block => {
hljs.highlightElement(block);
});
const section = textarea.closest('section');
if (!section?.parentElement) {
DEBUG && console.log('[mdc-lite] Could not find section to insert rendered content');
return false;
}
section.parentElement.insertBefore(rendered, section);
section.style.display = 'none';
const toolbar = document.querySelector('.react-blob-header-edit-and-raw-actions');
if (toolbar && !toolbar.querySelector('.mdc-segmented-control')) {
toolbar.insertBefore(createToggleButton(), toolbar.firstChild);
}
// Ensure toggle reflects actual display state (always rendered initially)
setViewMode('rendered');
DEBUG && console.log('[mdc-lite] Successfully rendered MDC');
return true;
}
/**
* Removes all MDC-related elements and restores original state
*/
function cleanup() {
document.getElementById('mdc-rendered')?.remove();
document.querySelector('.mdc-segmented-control')?.remove();
const original = document.querySelector('#read-only-cursor-text-area')?.closest('section');
if (original) original.style.display = 'block';
if (textareaObserver) {
textareaObserver.disconnect();
textareaObserver = null;
}
isActive = false;
DEBUG && console.log('[mdc-lite] Cleaned up');
}
/**
* Sets up a MutationObserver to watch for textarea content changes and re-render accordingly
* @returns {boolean} True if observer was successfully set up, false otherwise
*/
function setupTextareaObserver() {
const textarea = document.querySelector('#read-only-cursor-text-area');
if (!textarea) return false;
textareaObserver?.disconnect();
textareaObserver = new MutationObserver(() => {
DEBUG && console.log('[mdc-lite] Textarea content changed, re-rendering');
renderMDC();
});
textareaObserver.observe(textarea, {
childList: true,
subtree: true,
characterData: true
});
DEBUG && console.log('[mdc-lite] Textarea observer set up');
return true;
}
/**
* Handles page navigation changes, activating or deactivating MDC rendering based on URL
*/
function handlePageChange() {
if (MDC_FILE_REGEX.test(location.href)) {
if (!isActive) {
DEBUG && console.log('[mdc-lite] MDC file detected:', location.href);
isActive = true;
if (renderMDC()) {
setupTextareaObserver();
} else {
// Content not ready yet - retry with exponential backoff would be better, but keeping simple
let attempts = 0;
const interval = setInterval(() => {
attempts++;
if (renderMDC()) {
clearInterval(interval);
setupTextareaObserver();
} else if (attempts >= MAX_RENDER_ATTEMPTS) {
clearInterval(interval);
DEBUG && console.log('[mdc-lite] Timeout waiting for content');
}
}, RENDER_RETRY_INTERVAL);
}
} else {
// SPA navigation to another MDC file - re-render to sync toggle state
if (renderMDC()) {
setupTextareaObserver();
}
}
} else if (isActive) {
cleanup();
}
}
/**
* Initializes the userscript by setting up page change detection and handling the current page
*/
function init() {
handlePageChange();
// Monitor for SPA navigation changes
new MutationObserver(() => {
if (location.href !== currentUrl) {
currentUrl = location.href;
DEBUG && console.log('[mdc-lite] Navigation detected:', currentUrl);
handlePageChange();
}
}).observe(document, { subtree: true, childList: true });
DEBUG && console.log('[mdc-lite] Initialized');
}
if (document.readyState === 'loading') {
document.addEventListener('DOMContentLoaded', init);
} else {
init();
}
})();