A few months ago I was helping a friend review a revised freelance contract.
The client had "made a few small changes" - their words.
We had two PDF versions. No track changes. No diff. Just two documents that looked almost identical.
So we did what anyone does in that situation: opened both side by side and started reading. Line by line. Paragraph by paragraph.
Two hours later we found three changes. One of them was a payment clause that had been quietly reworded to cap late fees.
That experience stuck with me. Not because it was dramatic — but because it was completely avoidable.
The tools that exist weren't solving my actual problem
I knew diff checkers existed. I'd used them before for code.
But when I went looking for something that could handle:
- Long-form text documents (not just code)
- File uploads (not just paste)
- URL comparison (compare two web pages directly)
- Something that didn't upload my content to a server
I kept running into the same problems:
- Most tools are built for developers comparing code, not people comparing documents
- The ones that accepted files often uploaded them to external servers — not ideal for contracts or sensitive content
- URL comparison either didn't exist or was buried behind a signup wall
- The similarity score (how similar are these two texts, as a percentage?) was almost never shown
So I built my own.
What I focused on while building it
Browser-only processing. Everything runs in JavaScript inside your browser. No file ever touches a server. For contracts, legal documents, HR content — this matters.
Three comparison modes in one tool:
- Paste text directly (Content A vs Content B)
- Upload two files — TXT, CSV, JSON, HTML, MD, LOG
- Paste two URLs and compare the live page content directly
Word-level diff, not just line-level. Most diff tools highlight entire changed lines. Word-level highlighting shows you exactly which word changed inside a sentence — much more useful for documents.
Similarity score. A percentage that tells you at a glance how similar two texts are. Useful when you need a quick sanity check before diving into the details.
Inline and side-by-side views. Some people prefer reading changes in flow. Others prefer the two-column comparison. Both are there.
One thing I didn't expect
URL comparison sounds simple. Fetch two pages, strip the HTML, compare the text.
It's not simple.
Cross-origin requests get blocked by a lot of websites. Some pages load content dynamically via JavaScript, which means a basic fetch only gets the shell. Others serve different content based on location, device, or login state.
I ended up building a best-effort URL comparison — it works well for most public pages, but I document the limitation clearly: if a site blocks cross-origin requests, text paste is the fallback.
Honest tools tell you what they can't do.
Who actually uses this (from real feedback)
I built it for my own problem, but the use cases that came back surprised me:
- Writers comparing drafts before sending to editors
- HR teams checking policy document versions
- Developers comparing API response outputs during debugging
- Students checking if two sources are too similar before submission
- Anyone dealing with government or exam portals that return "updated" documents with no change log
That last one is very common in India specifically. Government portals update forms silently. You download a form, fill it out, then find out the portal has a newer version with different fields. A diff checker would have caught it in 10 seconds.
What I'm still working on
- Better handling of tables inside documents (HTML table comparison is messy)
- Export diff as PDF or HTML report
- Bulk comparison across more than two files
If you've run into a specific comparison problem that existing tools don't handle well — I'd genuinely like to hear it in the comments.
Try it
If this sounds useful: Content Difference Checker
No signup. No file upload. Works in your browser.
What's the most frustrating "these two documents look the same but aren't" situation you've dealt with?
I'm asking because half of my feature ideas come from people describing problems I hadn't thought of. The contract story above came from a friend. The government form problem came from a comment on my last post. Curious what else is out there.