Diff Checker: Compare Text Online for Free

A diff checker compares two versions of a text and shows exactly what changed. This free diff checker lets you paste text or upload a TXT, DOC, DOCX or PDF file for each side, then highlights removed text in red and added text in green. It suits writers, editors, developers and students.

What Is a Diff Checker?

A diff checker is a utility that compares two blocks of text and reports every difference between them. The name comes from the Unix diff command, which has listed changes between two files for decades. The idea is the same here: one version is the baseline and the other is the revision.

Text that exists in the original but not in the modified version counts as a deletion. Text that appears only in the modified version counts as an addition. A replaced word counts as both, because the old word was removed and the new word was added.

The comparison works on the exact characters you provide, so small formatting differences such as capital letters, punctuation and extra spaces can show up as changes. That precision is what makes a text comparison reliable for catching a single altered number or a missing comma.

How to Use the Diff Checker

You can compare two texts in under a minute by filling both sides and pressing one button. Follow these steps:

1. Under Original Text, keep the Text tab selected and paste the older version into the box that says "Paste your original text here...".
2. Under Modified Text, keep the Text tab selected and paste the newer version into the box that says "Paste your modified text here...".
3. To compare a document instead, switch either side to the File tab, click the area labeled "Click to select or drag a file" and choose a .doc, .docx, .pdf or .txt file. The file name appears once it is selected. You can mix the two methods, for example a file on the left and pasted text on the right.
4. Click Compare. Each side needs a selected file or at least 10 characters of text, otherwise you will see a message telling you which side to fix.
5. Scroll to Comparison Results. The Old Version panel shows removed text in red and the New Version panel shows added text in green.
6. Click Clear All to empty both text boxes and file selections before starting a new comparison.

Worked Example: Spotting a Small Edit in a Notice

Suppose you sent a team notice and someone edited it before it went out. You paste the version you wrote into Original Text and the version that was sent into Modified Text.

• Original: The team meeting is on Monday at 9 AM in Room 4.
• Modified: The team meeting is on Tuesday at 10 AM in Room 4.

After you click Compare, the Old Version panel highlights "Monday" and "9" in red. The New Version panel highlights "Tuesday" and "10" in green. Everything else, including "Room 4", stays uncolored because it matches in both versions.

You can read this at a glance: the day and the start time changed, the room did not. Without a comparison, you could easily skim past a two-character change like 9 to 10. The same approach works on a 3,000-word article, where the highlights reveal edits you would never find by rereading.

How Do You Read the Comparison Results?

Read the results by matching each color to its panel: red marks text that was removed or replaced, and green marks text that was added or substituted in. Uncolored text is identical on both sides.

Only a few short highlights

This is the expected result for a light edit, such as a corrected typo or an updated price. Check each colored fragment to confirm it is an intended change.

Almost everything is highlighted

If most of both panels is colored, the two texts are very different, or you pasted the wrong versions. First confirm that the older text is on the Original side. Then check whether one version was reformatted, for example with different line breaks, which can make unchanged wording look changed.

No highlights at all

If nothing is colored, the two texts are identical as far as the tool can see. That is a useful confirmation when you need proof that a copy, export or migration did not alter the wording.

Highlights you did not expect

Look closely at spaces, line breaks, curly versus straight quotes and capitalization. These invisible or near-invisible differences are the most common cause of surprise highlights. Clean the text on both sides the same way, then compare again.

Who Should Use a Text Comparison Tool?

Anyone who revises text and needs to know what really changed benefits from a side-by-side review of old and new wording. These are the situations where it earns its place:

• SEO and content teams: compare a page before and after a content refresh, check that a rewritten title or meta description changed only what you intended, or confirm that migrated copy matches the original.
• Editors and writers: review a colleague's revisions to a draft, or check your own second draft against the first.
• Developers: compare configuration snippets, SQL queries, HTML fragments or JSON that you paste in as plain text.
• Students and researchers: check a paraphrased passage against its source wording, or compare two versions of an essay.
• Operations and admin staff: compare two versions of a policy, template email or product description before publishing.

For contracts or legal wording, the highlights show you where to look, but a qualified person should still review the meaning of every change.

Best Practices, Common Mistakes and Troubleshooting

Better input produces a cleaner comparison, so a little preparation saves time reading the results.

Put the older version on the left

The Original side is the baseline. If you swap the sides, additions appear as deletions and the story you read is reversed.

Compare like with like

Copying one version from a web page and the other from a Word file often brings different spacing and line breaks. If capitalization is only noise, run both texts through a text case converter first so that only real wording changes are highlighted.

Break long documents into sections

A full report is easier to review one chapter at a time. Smaller chunks keep the colored fragments easy to scan and make it obvious which part of the document changed.

Tidy lists before comparing them

When you are comparing keyword lists or URL lists, repeated entries can drown out the real differences. Use a duplicate line remover on each list, or turn a column into a single line with a comma separating tool if that format is easier to read.

Fix the "at least 10 characters" message

Both sides need a selected file or at least 10 characters of text. A very short phrase will not run, so include a full sentence. Check that the Text or File tab you want is the one currently selected on each side.

If a file will not upload or looks empty

Use only .doc, .docx, .pdf or .txt files. If a file is rejected, try saving it as plain text or pasting its contents into the text box instead. Scanned PDFs that contain only images have no text to extract, so the comparison will have nothing to work with.

Count characters when you need a quick sanity check

If two versions look the same but still show differences, a quick look at a character frequency counter can reveal stray symbols or extra characters one version contains.

Can It Compare JSON, Code, PDF or Excel Data?

Yes for anything you can paste or save as readable text, with a few honest limits. Code, HTML, CSS and JSON compare well when pasted into the boxes, but the tool treats them as plain text. It does not understand syntax, so reordering keys in a JSON object or changing indentation will appear as changes even when the data means the same thing.

PDF files can be uploaded, but you are comparing extracted text, not page layout. Fonts, images, columns and tables are not compared. Text pulled from a PDF can also carry odd line breaks, which may add highlights that were not in the visible document.

For spreadsheets, there is no Excel file upload. Copy the cells you want to compare and paste them as text, or save the sheet as a .txt file first. Remember that the tool reports textual differences only: it does not judge whether a change is correct, good or harmful.

You can find related utilities for cleaning and formatting your text in the Text Utility Tools category.

When you need to know what changed between two versions, the fastest route is to paste both, click Compare and read the red and green highlights. Add your original and modified text above, or upload two files, and run the comparison now.