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README.md

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-license: mit
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+# HTML‑Viewer.org
+> A browser‑native HTML/CSS/JS sandbox with two‑way element‑code sync and visual preview editing
+
+🔗 Live site: https://html-viewer.org
+
+## What is this tool for?
+When you write or study web code, it can be hard to tell which lines of code produce which parts of the rendered page. HTML‑Viewer solves this pain point.
+
+This is an all‑in‑one web sandbox that runs entirely inside your browser. You don’t need to install software or create accounts. Paste your HTML, CSS and JavaScript, and you get instant live preview.
+
+The standout capability is **bidirectional highlighting**:
+- Click code on the left → the corresponding page element lights up in preview
+- Click content in preview → jump straight to the matching source code lines
+
+This is extremely helpful for debugging broken layouts, learning how HTML works, and hunting down where a particular style or text comes from.
+
+On top of code inspection, you can also edit content directly inside the preview window. Use the toolbar to make text bold, change font sizes, add images, or build lists. The tool automatically writes the correct HTML markup for you, so you avoid typing repetitive tags manually.
+
+All parsing, rendering and file handling happens locally on your device. Your code never gets uploaded to any server, keeping your work private.
+
+## Main capabilities
+### Two‑way sync highlight
+- Trace connections between source code and rendered webpage elements
+- Toggle sync on or off to avoid interference while writing large blocks of code
+
+### Visual WYSIWYG editing on preview
+- Format text: bold, italic, font‑size, alignment
+- Insert images, ordered lists, unordered lists
+- All edits reflect instantly into the source code editor
+
+### Helpful developer utilities
+- Import local HTML / CSS / JS files
+- Format messy code with one click
+- Basic HTML syntax error detection
+- Export final code to your computer
+- Dark mode
+- Collapse/expand nested code blocks
+- Open preview or source in new tab
+
+## Who can benefit
+- People learning HTML/CSS/JS and want to see real‑time cause‑and‑effect
+- Developers testing small code snippets and quick prototypes
+- Designers checking static page outputs
+- QA personnel investigating display bugs
+- Hobbyists building small web demos and tools
+
+## Preview assets
+![Two‑way highlight demo](screenshot‑two‑way‑highlight.png)
+![Visual editing toolbar](screenshot‑visual‑edit‑toolbar.png)
+
+Optional demo video: `demo‑html‑viewer‑usage.mp4`
+Shows full workflow of bidirectional highlight and preview‑based visual editing.
+
+## Quick start
+1. Open https://html-viewer.org in your browser
+2. Paste code, or import local files
+3. Watch live preview update on the right
+4. Use bidirectional highlight to explore code‑element mapping
+5. Use visual edit mode to modify content directly on preview
+6. Format code and export to local files when done
+
+## Important notes
+- Best suited for snippets, demos and learning. It is not intended to replace full‑featured IDEs for large production projects.
+- Visual editing works well for content and simple formatting. Advanced layout logic still requires manual code editing.
+- All processing is local, no code is transmitted externally.
+
+## License
+MIT