The HTML diff tool parses two HTML documents using the browser's built-in DOMParser and compares them at the element level — detecting added tags, removed tags, changed attributes, and text content modifications. Unlike plain text diff tools, HTML diff understands document structure so reformatted but identical code won't produce false positives.
How to Use the HTML Diff Tool
Comparing HTML files is a common task when reviewing template changes, debugging visual regressions, or auditing edits to web pages. Our free HTML diff tool parses both documents and compares them at the DOM level — giving you element-level precision rather than a raw line-by-line text comparison.
Step 1: Paste Your HTML Documents
Paste the original (older) HTML into the left panel and the modified (newer) version into the right panel. The tool accepts full HTML pages with DOCTYPE declarations, partial templates, component snippets, or even bare HTML fragments. There is no size limit for typical documents.
Step 2: Click Compare HTML
Click the Compare HTML button to run the comparison. The tool uses the browser's built-in DOMParser to parse both documents into DOM trees, then serializes them with normalized formatting before computing the line-level diff. This means minor formatting differences — extra spaces, attribute ordering — won't create false positives.
Step 3: Read the Color-Coded Output
Lines highlighted in green with a + prefix were added. Lines in red with a - prefix were removed. Lines in yellow show modified elements. HTML tags are highlighted in blue, attributes in green, and attribute values in orange so you can quickly spot structural versus content changes.
Step 4: Choose Your View Mode
Use "Side by Side" to see original and modified in parallel columns — ideal for seeing context around each change. Switch to "Unified" for a compact single-column diff with +/- prefixes, similar to git diff output. Use "Rendered Preview" to see both documents displayed as a browser would render them side by side — great for catching visual regressions.
Copy the Diff
Click "Copy Diff" to copy the unified diff output to your clipboard — ready to paste into a code review, bug report, or documentation. The diff uses standard unified diff format compatible with most diff viewers and version control systems.
FAQ
Is this HTML diff tool free?
Yes, completely free with no account or signup required. All comparison happens in your browser — your HTML code is never sent to any server.
Is my HTML code private?
Yes. The entire diff runs in client-side JavaScript. Nothing is uploaded or stored. You can safely use this tool with proprietary templates, internal codebases, or sensitive HTML content.
How does HTML diff differ from plain text diff?
HTML diff parses both documents into DOM trees and compares at the element level — detecting added/removed tags, changed attributes, and modified text content. Plain text diff just compares raw lines, which means a reformatted but semantically identical HTML file would show many false differences.
What does the rendered preview mode show?
The rendered preview shows both HTML documents displayed visually in sandboxed iframes side by side, so you can see the visual appearance of each document as a browser would render it. This helps you spot visual regressions alongside the structural diff.
Can I compare HTML fragments, not full pages?
Yes. The tool accepts any HTML — full pages with DOCTYPE, partial templates, component snippets, or even a single div. DOMParser handles fragments gracefully so you can compare any valid HTML input.
What does the yellow highlight mean?
Yellow highlighting indicates a modified element — the element exists in both documents but has changed attributes, text content, or child structure. Green means added (only in the new version) and red means removed (only in the original).