HTML Viewer & Editor
Edit, format, preview and explore HTML — everything runs in your browser
Sandboxed preview — scripts run but can't reach the rest of the app.
HTML Viewer & Editor — Complete Guide & Instructions
MakeCard HTML Viewer & Editor is a free in-browser workbench for HTML. Edit or paste markup in the Code tab, pretty-print it with Format, inspect the element hierarchy in the DOM Tree tab, and render it live in a sandboxed Preview iframe where scripts run safely isolated. Import .html/.txt files, export your work, copy to clipboard, and flip between light and dark editor themes — no setup, no sign-up.
How to Use HTML Viewer & Editor
- 1 Paste your HTML into the Code tab, click "Sample" for a starter page, or "Import file" to load an .html/.txt file.
- 2 Press "Format" to pretty-print messy markup with proper indentation.
- 3 Switch to the "DOM Tree" tab to explore the parsed element hierarchy — Expand all / Collapse all controls included.
- 4 Open the "Preview" tab to render the page inside a sandboxed iframe.
- 5 Use "Copy" or "Export file" to save your work, and toggle 🌙 Dark / ☀ Light for the editor theme.
Key Features & Capabilities
- Three work modes: code editor, interactive DOM tree, and live preview.
- One-click HTML formatter for consistent indentation.
- Sandboxed preview iframe — scripts run but cannot reach the rest of the app.
- Import .html/.htm/.txt files and export the result as a file.
- Expandable/collapsible DOM tree for structure inspection.
- Dark and light editor themes.
- 100% client-side — your markup never leaves the browser.
Supported Formats & Specifications
| Parameter | Specification |
|---|---|
| Tabs | Code, DOM Tree, Preview (sandboxed iframe) |
| File I/O | Import .html/.htm/.txt; export to file; clipboard copy |
| Preview Safety | iframe sandbox="allow-scripts" — isolated from the app |
| Extras | Formatter, sample loader, dark mode |
Practical Everyday Use Cases
- Testing an HTML snippet before pasting it into a CMS or email template.
- Inspecting the DOM structure of markup copied from a webpage.
- Formatting minified or messy HTML for readability.
- Teaching HTML — students edit code and watch the preview update.
- Quickly verifying a fragment renders correctly without spinning up a server.
Pro Tips for Best Results
- Use the DOM Tree tab to debug unclosed tags — the parser shows exactly how the browser interpreted your markup.
- The preview is sandboxed with allow-scripts, so scripts run but cannot escape — still, avoid pasting third-party scripts you do not trust.
- External CSS/JS links will try to load in the preview; inline styles are guaranteed to render.
- Format first, then preview — clean indentation makes broken structure obvious.
Common Problems & Solutions
Check for unclosed tags or malformed markup in the DOM Tree tab — the browser's error recovery may be restructuring your HTML differently than expected.
Linked stylesheets, fonts, or scripts on other domains may be blocked by the sandbox or the remote server's headers — inline the critical parts for a reliable preview.
Privacy & Security
100% Client-Side Execution
Editing, formatting, and previewing all happen inside your browser — no code or file content is uploaded to any server.
Frequently Asked Questions
Everything you need to know about using HTML Viewer & Editor
Yes — completely free with no sign-up. Everything runs in your browser, including formatting, preview, and file import/export.
Yes — the Preview tab runs in a sandboxed iframe with scripts allowed, so inline JS executes safely isolated from the rest of the app.
Click Import file and pick an .html, .htm, or .txt file — its contents load into the code editor instantly.
Format re-indents your markup but does not repair syntax errors — check the DOM Tree tab to see how the browser actually parsed it.
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100% free, browser-based, and private. No installation, registration, or file upload to external servers required.
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