ZeroServer.tools

HTML Compare

Compare two HTML documents: source line diff plus a rendered side-by-side preview.

Original HTML (Left)

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Modified HTML (Right)

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Source Line Diff

1<!DOCTYPE html>

2<html>

3<head>

4- <title>Landing Page</title>

4+ <title>Landing Page v2</title>

5</head>

6<body>

7- <h1>Welcome to our site</h1>

7+ <h1>Welcome to our platform</h1>

8- <p>We build tools for developers.</p>

8+ <p>We build fast, free tools for developers.</p>

9- <button>Sign Up</button>

9+ <button class="cta">Get Started</button>

10</body>

11</body>

11</html>

12</html>

Added: +5 linesRemoved: -4 linesUnchanged: 7 lines

How HTML Compare works

This tool compares two HTML documents entirely in your browser using a line-based Myers diff algorithm, the same approach used by git diff. Nothing you paste is uploaded anywhere — both the diffing and the rendering happen locally on your device.

Switch to Source Diff to see line-by-line additions and removals highlighted side by side, or Rendered Preview to see both documents rendered visually next to each other inside sandboxed <iframe sandbox> elements — scripts are disabled in both previews, so it's safe to compare markup from an untrusted source.

Common use cases

Template revisions: spot exactly what changed between two versions of an email template or landing page.
CMS output diffing: compare HTML exported before and after a content edit or plugin update.
Visual regression checks:confirm a markup change doesn't unexpectedly alter the rendered layout.

Private & free — this tool runs entirely in your browser.