HTML Site Comparator — Free Online
Upload two website zip files to instantly compare every file. See what changed, what was added, and what was deleted — with a line-by-line diff viewer for changed files. Runs entirely in your browser.
What This Tool Does
The HTML Site Comparator takes two zip files — each containing a complete website — and compares every file between them. It extracts both archives in your browser, matches file paths, and categorises each file as unchanged, added, deleted, or changed.
For changed files, you can click through to a line-by-line diff viewer that highlights exactly what was added or removed. This is essential for reviewing site updates, verifying deployments, auditing template changes, or comparing staging vs production builds.
How to Use the HTML Site Comparator
- Zip each version of your website into a .zip file (the original and the updated version)
- Drag and drop (or browse) Site A into the left drop zone and Site B into the right drop zone
- Click Compare Sites — the tool extracts both zips and compares all files
- Review the summary: unchanged, added, deleted, and changed file counts
- Click any changed file to open the line-by-line diff viewer
- Green lines are additions (in Site B), red lines are deletions (from Site A)
Use Cases
| Scenario | How This Tool Helps |
|---|---|
| Pre-deployment review | Compare your staging build against production to verify only intended changes are present |
| Template auditing | Ensure a CMS template update did not introduce unintended changes across pages |
| Version tracking | Compare two saved snapshots of a static site to see what changed between releases |
| Collaboration | Review a colleague's changes to a static site without requiring Git |
| Migration validation | After migrating a site to a new platform, compare the output HTML to confirm nothing was lost |
How the Diff Algorithm Works
The comparator uses a longest common subsequence (LCS) algorithm to produce line-by-line diffs. This is the same fundamental approach used by diff on Unix systems and by Git internally. It finds the longest sequence of lines that appear in both files in order, then marks everything else as an addition or deletion.
The result is a clear, colour-coded view where green lines show content that exists only in Site B (additions), red lines show content that exists only in Site A (deletions), and grey lines show unchanged context. Line numbers for both the original and updated file are displayed side by side.
Privacy & Security
All zip extraction and file comparison runs in your browser using JavaScript and JSZip. No files are uploaded to any server. This is especially important when comparing websites that contain API keys, internal URLs, authentication tokens, or customer data in their HTML or configuration files.
💡 Need to compare plain text instead of entire websites? Use the Text Compare tool for a quick side-by-side diff. For formatting HTML before comparing, try the HTML Formatter.
Related Guides & Tutorials
Comparison Workflow Tools
- Need to compare just two blocks of text? The Text Compare tool gives you a fast side-by-side diff.
- Format your HTML consistently before comparing so that whitespace differences do not produce noise. → HTML Formatter
- Working with JSON config files inside your site? Format them first. → JSON Formatter
- Minifying CSS before deployment? Compare minified vs unminified output. → CSS Minifier
- Validating HTML structure independently? → XML Validator