HTML Previewer

The HTML Previewer is a free online tool that lets you paste raw HTML code and instantly see how it renders in a browser. Whether you are building an email template, debugging a blog post, testing AI-generated markup, or learning HTML basics, this tool gives you a live visual preview without needing to save files or open a code editor.

Who Uses an HTML Previewer

Email marketers use it to test newsletter layouts before sending to thousands of subscribers — catching broken tables and misaligned columns before they go live. Web developers paste code snippets to verify rendering without switching to a browser tab. Content managers preview blog posts exported from CMS platforms like WordPress, Ghost, or Substack to ensure formatting survived the transfer. Students learning HTML get instant feedback on every tag they write, turning abstract syntax into visible results. And anyone working with AI-generated HTML can paste Claude or ChatGPT output to verify it actually looks right before using it.

How It Works

Paste or type HTML into the input area, and the rendered output appears instantly in the preview pane below. The preview is sandboxed using an iframe for security — scripts will not execute, keeping your browser safe while you experiment with any markup. A 300-millisecond debounce prevents the preview from flickering while you type, giving you a smooth live-editing experience.

Built-In Formatting Tools

The Prettify button auto-formats messy or minified HTML into readable, indented code with proper nesting — following the same conventions described in the MDN HTML guide. The Minify button does the reverse — stripping whitespace and comments to produce the smallest possible output, useful for email templates with character limits or embedding HTML in other systems. Copy puts your HTML on the clipboard with one click. And the responsive toggle previews your work at desktop, tablet (768px), and mobile (375px) breakpoints — essential for testing layouts that need to work across devices.

Starter Templates

Start from one of five ready-made templates instead of a blank page. The templates are loaded from our database, so new ones appear automatically as we add them:

Email Newsletter

A complete newsletter layout with branded header, body text, call-to-action button, and unsubscribe footer. Uses inline CSS for maximum email client compatibility, following the patterns recommended by Can I Email.

Blog Post

A structured article with headings, paragraph text, lists, inline code samples, and a styled blockquote. Demonstrates semantic HTML using article, h1, h2, ul, and blockquote elements — the same markup structure that search engines prefer for content indexing.

Landing Page

A hero section with gradient background and call-to-action button, plus a three-column feature grid using CSS grid layout. Shows how to combine visual design with semantic structure in a single HTML document.

Data Table

A formatted sales report with header row, numeric alignment, and color-coded status badges. Demonstrates proper table structure using thead, tbody, th, and td — skills that transfer directly to building data tables in tools like the Board Feet Calculator or any data-heavy application.

AI Exposure Comparison

A multi-row comparison table with color-coded risk scores, role descriptions, and smart pivot recommendations. Shows advanced table techniques including colspan, conditional row colors, and badge-style spans — patterns useful across any ProCalc domain from Finance to Engineering.

Stats and Analysis

A live stats bar tracks four metrics as you work: character count (total HTML length including tags), word count (visible text only with tags excluded), line count, and HTML element count (number of opening tags). These are useful for checking email template size limits — Gmail clips emails over 102KB — estimating content length for SEO, or verifying that your markup structure matches expectations.

Privacy and Security

No signup required, no data sent to any server. Your HTML stays entirely in your browser, rendered in a sandboxed iframe that prevents script execution and blocks access to your cookies, local storage, and other page data. Templates are loaded from our database, but everything you type or paste remains on your device. Use this tool freely with confidential content, proprietary code, or client work.

HTML Quick Reference

HTML documents are built from elements — tags that wrap content and give it meaning. The full HTML reference at MDN covers every element, but here are the ones you will use most often:

Structural Elements

Use div as a generic container, section for thematic groups, article for self-contained content, header and footer for introductory and closing content, nav for navigation, and main for the primary content area. These semantic elements help screen readers and search engines understand your page structure.

Text and Content

Headings from h1 (largest, most important) through h6 (smallest) create a document outline. Paragraphs use p, inline text styling uses strong (bold) and em (italic), and br creates line breaks. For quoted content, use blockquote. For code samples, use code for inline snippets and pre for preformatted blocks.

Lists and Tables

Unordered lists (ul with li items) create bullet points; ordered lists (ol) create numbered sequences. Nest lists by placing a new ul or ol inside an li. Tables use a nested structure: table contains thead and tbody, which contain tr rows, which contain th (header) or td (data) cells. Use colspan and rowspan to merge cells across columns or rows.

Inline CSS Essentials

When external stylesheets are not available — as in email templates or embedded HTML — inline styles are the standard approach. The CSS reference at MDN documents every property, but the most common ones for inline use are:

Typography

Control typeface with font-family (stick to web-safe fonts like Arial, Georgia, and Courier for emails), size with font-size (use px for consistency), weight with font-weight (400 normal, 700 bold), and color with the color property. Line-height controls vertical spacing between lines — 1.5 to 1.8 works well for body copy.

Spacing and Borders

Padding creates space inside an element border; margin creates space outside it. Both accept values in px, em, or rem. Borders combine width, style, and color: border: 1px solid #e5e7eb is a standard light border. Add border-radius for rounded corners — 4px for subtle rounding, 50% for circles. Use border-collapse: collapse on tables to remove gaps between cells.

Layout

Modern CSS layout uses flexbox (display: flex with justify-content and align-items) and grid (display: grid with grid-template-columns). For email compatibility, stick to table-based layouts or simple block elements with explicit widths. The display property controls element flow: block takes full width, inline flows with text, inline-block combines both, and none hides the element.

Colors

Specify colors as named values (red, blue), hex codes (#FF0000), RGB (rgb(255, 0, 0)), or RGBA with transparency (rgba(255, 0, 0, 0.5)). Background-color fills an element; color sets text. For gradients, use background: linear-gradient(135deg, #1e3a5f, #2563eb) — though note that gradients do not render in Microsoft Outlook.