Text Diff Checker — Compare Text Online, No Upload, Free
Compare two blocks of text and see added, removed, and unchanged lines highlighted side by side. Uses a line-by-line LCS diff — the same approach as Git. Runs in your browser: no upload, no account.
How to use this tool
- Paste original text in the left panel and revised text in the right.
- Review the highlighted differences.
- Copy the diff summary if needed.
About Diff Checker
A diff checker compares two versions of text and shows you exactly what changed between them: which lines were added, which were removed, and which stayed the same. This tool works at the line level, treating each line as an indivisible unit. It splits both inputs on line breaks and then aligns them to find the longest sequence of lines they have in common, marking everything that falls outside that common sequence as either an addition (present only in the changed version) or a removal (present only in the original).
The underlying technique is a longest-common-subsequence (LCS) diff, the same family of algorithm that version-control systems like Git use to display changes. The LCS approach finds the largest set of lines that appear in the same order in both versions, anchors the output around them, and reports the rest as edits. This produces a stable, readable result: unchanged lines stay put as reference points, and edits cluster around the lines that actually differ rather than the whole file appearing to change because one line shifted. The tool also gives you a running tally of added, removed, and unchanged line counts so you can see the size of a change at a glance.
Because the comparison is line-based, a line that was edited rather than wholly inserted or deleted shows up as a removal of the old line paired with an addition of the new one, not as an inline highlight of the changed words within it. This is the expected behavior of line diffs and is usually what you want for code and structured text, where a line is the natural unit. It does mean that reformatting, such as rewrapping a paragraph or changing indentation, can register as many changes even when the meaning is identical, since every reflowed line is now technically different from before.
The common use cases are code review and revision tracking: comparing two versions of a config file, a function, a SQL query, or a piece of prose to confirm what an edit actually did. People also use it to compare contract drafts, spot unintended changes between two copies of a document, verify that a copy-paste preserved content exactly, and check the difference between expected and actual program output. Everything runs locally in your browser, so you can compare confidential code or legal text without it ever leaving your device.
Frequently Asked Questions
- How does the comparison actually work?
- The tool splits both blocks of text into lines and runs a longest-common-subsequence (LCS) diff, the same approach version-control tools use. It finds the largest set of lines that appear in the same order in both inputs, treats those as unchanged anchors, and reports everything else as either an added line (only in the changed side) or a removed line (only in the original side).
- Does it highlight changes word by word within a line?
- No. It compares whole lines, so an edited line is shown as the original line removed and the new line added, rather than highlighting the specific words that differ. This is standard for line-based diffs and matches how code reviews typically present changes.
- Why does a small wording change mark a whole line as changed?
- Because the unit of comparison is the entire line. If you change a single word, the old version of that line no longer matches the new version, so the tool reports one removal and one addition. To see finer detail, keep each sentence or statement on its own line before comparing.
- What do the added, removed, and unchanged counts mean?
- They summarize the diff: added is the number of lines present only in the changed text, removed is the number present only in the original, and unchanged is the number of lines common to both. The totals give you a quick sense of how large an edit is before you read the line-by-line output.
- Why does reformatting show up as many changes?
- Line diffs treat any difference in a line, including whitespace, indentation, or where a paragraph wraps, as a change. If you reflow a paragraph or reindent a block, every affected line becomes a new line as far as the comparison is concerned, even though the content reads the same. Comparing before and after reformatting is the cleanest way to avoid this.
- What is this useful for besides code?
- Any time you need to know what changed between two texts: comparing contract or document drafts, checking two configuration files, verifying that a paste preserved content exactly, reviewing edits to a translation, or comparing expected versus actual output from a program or test.
- Is my text sent to a server?
- No. Both inputs are compared entirely in your browser. Nothing is uploaded, logged, or stored, so you can safely diff confidential source code, contracts, or private documents.
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<iframe src="https://brevio.pro/embed/diff-checker" width="100%" height="600" loading="lazy" style="border:1px solid #e5e5e5;border-radius:8px" title="Diff Checker — brevio"></iframe> <p style="font:12px/1.4 sans-serif"><a href="https://brevio.pro/tools/diff-checker">Diff Checker</a> by <a href="https://brevio.pro">brevio</a></p>