Adding a built-in code editor (for HTML, CSS, JS)

 That’s a great goal 👏 — building your own CMS like WordPress and adding a built-in code editor (for HTML, CSS, JS) is a powerful feature for users who want full control over styling and scripts.

Let’s go through the best free editor choices specifically for this use case.

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🧠 Your Goal Recap

You want:

• A browser-based code editor (not WYSIWYG like TinyMCE).

• It must let users write and edit HTML, CSS, and JavaScript inside your CMS.

• It should have syntax highlighting, auto-completion, and a modern UI (like VS Code).

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✅ Best Free Editors for Embedding in a CMS

1. Monaco Editor (💡 The same editor used in VS Code)

Website: https://microsoft.github.io/monaco-editor/
License: MIT (Free & Open Source)

✨ Features

• Syntax highlighting for 100+ languages (HTML, CSS, JS, PHP, etc.)

• Auto-completion and IntelliSense-like suggestions

• Error checking (e.g., syntax errors in JS)

• Multiple themes (dark/light)

• Extremely customizable and fast

🧩 Example Integration

<div id="editor" style="height:500px;border:1px solid #ccc;"></div>

<script src="https://cdn.jsdelivr.net/npm/monaco-editor@0.44.0/min/vs/loader.js"></script>
<script>
require.config({ paths: { 'vs': 'https://cdn.jsdelivr.net/npm/monaco-editor@0.44.0/min/vs' }});
require(['vs/editor/editor.main'], function() {
  monaco.editor.create(document.getElementById('editor'), {
    value: "/* Write your CSS or JS here */",
    language: "javascript", // you can switch between 'html', 'css', 'javascript'
    theme: "vs-dark"
  });
});
</script>

🟢 Best For

CMS platforms where users want a developer-level experience — like WordPress’s “Theme Editor”.

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2. CodeMirror 6

Website: https://codemirror.net/
License: MIT (Free & Open Source)

✨ Features

• Fast and lightweight

• Supports HTML, CSS, JS, PHP, etc.

• Syntax highlighting and linting

• Works well in embedded CMS environments

• Can be customized with plugins (auto-complete, themes, line numbers, etc.)

🧩 Example Integration

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/6.65.7/codemirror.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/6.65.7/codemirror.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/6.65.7/mode/javascript/javascript.min.js"></script>

<textarea id="editor">// Write your JS here</textarea>
<script>
var editor = CodeMirror.fromTextArea(document.getElementById('editor'), {
  lineNumbers: true,
  mode: "javascript",
  theme: "monokai"
});
</script>

🟢 Best For

Lightweight CMS systems or admin panels that want a fast, embeddable code editor with minimal setup.

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3. Ace Editor

Website: https://ace.c9.io/
License: BSD (Free & Open Source)

✨ Features

• Syntax highlighting for 110+ languages

• Themes (Monokai, GitHub, Solarized, etc.)

• Find/replace, auto-indent, code folding

• Used in many popular tools like jsFiddle, Cloud9 IDE

🧩 Example Integration

<div id="editor" style="height:500px;width:100%;">/* Write code here */</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/ace/1.32.0/ace.js"></script>
<script>
var editor = ace.edit("editor");
editor.session.setMode("ace/mode/javascript");
editor.setTheme("ace/theme/monokai");
</script>

🟢 Best For

CMS developers who want a solid, proven, and easy-to-embed editor with minimal setup.

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🔍 Quick Comparison

Feature	Monaco	CodeMirror	Ace
License	MIT	MIT	BSD
Size	Large (~2MB)	Medium	Medium
Language Support	100+	100+	100+
Auto-completion	✅ Advanced	⚙️ Basic	⚙️ Basic
Linting	✅ Built-in	✅ via plugin	✅ via plugin
Themes	✅ Many	✅ Many	✅ Many
Best For	Full-featured CMS	Lightweight CMS	General purpose

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🏁 Recommendation

• If you want a modern and professional editor (like VS Code) → Monaco Editor 🥇

• If you want something faster and simpler → CodeMirror 6 🥈

• If you want a battle-tested, easy-to-use option → Ace Editor 🥉