Text Compare & Diff Checker — free online
Compare two blocks of text and highlight every added, removed and changed line. A free diff checker that runs in your browser — nothing is uploaded.
About the Text diff tool
Comparing two versions of something by reading them side by side is unreliable in a way most people underestimate. The eye skips over a changed digit, a flipped negation, a swapped name. Anyone who has tried to find what changed between two drafts of a contract, two exports of a configuration file, or two revisions of a translation knows that the difference is often a single character in a thousand lines, and that finding it manually is a matter of luck.
A diff removes the luck. It compares the two texts line by line and marks precisely what was added, what was removed and what stayed the same, so the answer to "what actually changed" takes a second rather than an afternoon. It is the same mechanism behind version control, code review and every "track changes" feature, applied to any two blocks of text you happen to have.
The everyday uses have little to do with programming. Checking what a colleague altered in a document when they did not use track changes. Verifying that a configuration file on one server matches another. Confirming which lines of a translated file are still missing. Comparing yesterday's data export with today's to see what moved. Any time two things should be identical and you need to know whether they are, this is the fastest way to find out.
Comparison here is line-based, which is the right granularity for most work but worth understanding. A line with one word changed is shown as a removal and an addition rather than as a highlighted word, so a text of long unbroken paragraphs will report whole paragraphs as changed even when the edit was tiny. Breaking the text at sentences before comparing gives a much more precise picture when that happens.
How it works
Paste the original
Put the earlier or reference version in the left pane. Both texts stay in your browser tab.
Paste the changed version
Put the newer or suspect version on the right. The comparison runs as soon as both sides have content.
Read the differences
Added and removed lines are marked and counted, so you can see at a glance how much actually changed.
Frequently asked questions
- Does it compare word by word or line by line?
- Line by line. A line with a single altered word appears as one removal plus one addition rather than as a highlighted word within the line. That is ideal for code, configuration and lists, where lines are naturally short. For flowing prose it can be blunt — splitting long paragraphs onto separate lines before comparing makes the result far more readable.
- Can I compare two files?
- Open each file and paste its contents into the corresponding pane. That keeps both documents on your own machine, which is the point of a browser-based diff, and it also lets you compare just a section — one function, one chapter, one config block — rather than the whole file, which is often what you actually want.
- Why is everything showing as changed?
- Usually different line endings. Windows terminates lines with a carriage return and line feed, Unix and macOS with a line feed alone, and a file that has crossed between the two can differ on every single line invisibly. Trailing whitespace and a switch between tabs and spaces cause the same effect. Normalise one side and compare again.
- Is it case sensitive?
- Yes. "Error" and "error" are reported as different, which is correct for code, identifiers, configuration values and anything where case carries meaning. If you are comparing prose and only care about substance, converting both sides to lowercase first with the Change case tool will filter out capitalisation noise.
- How large can the two texts be?
- Thousands of lines on each side compare quickly. Very large inputs are limited by the browser rendering that much marked-up text rather than by the comparison itself, so the tab may feel sluggish well before the algorithm struggles. Comparing the relevant section rather than two entire large files is both faster and easier to read.
- Can it merge the two versions?
- No — this tool shows you what differs and leaves the decision to you. Merging means choosing which side wins for every conflicting change, which needs a purpose-built merge tool and, usually, someone who understands the content. Seeing the differences clearly is normally what unblocks the task anyway.
- Is my text sent to a server?
- No. Both texts are compared in JavaScript inside your browser tab and neither is transmitted, stored or logged. Diffs are routinely run on contracts, credentials, configuration files and unreleased drafts, so keeping them local is not a nicety. Closing the tab discards both sides entirely.