Text Diff Checker
Compare two texts line by line and see what was added, removed, or unchanged. Runs in your browser, nothing uploaded. Great for drafts, lists, messages, and code snippets.
Your texts stay in the browser and are not uploaded. The comparison runs locally only, using an LCS algorithm. The tool is meant for everyday work with text; it is not a substitute for a professional review of contracts or sensitive documents.
The text diff checker is a free browser tool for comparing two pieces of text and finding the differences between them. Paste the original text on one side, the text to compare on the other, and the tool shows you line by line what was added, what was removed, and what stayed the same. Results are available in two view modes: a unified diff view (every line with a +/-/space marker) and a side-by-side view (left/right). The tool is handy for comparing drafts of articles, messages, lists, code snippets, translation versions, and any text that has been edited. The comparison is based on the classic LCS (Longest Common Subsequence) algorithm, which is deterministic and always returns the same result for the same inputs. The tool supports a few simple options: ignore case, ignore whitespace differences, and ignore blank lines. These options only affect the key used for the comparison; the original text is always shown exactly as it was typed. Everything happens in your browser: the texts, the options, and the result are never uploaded or stored. The tool is meant for everyday work with text; it is not a substitute for a professional review of contracts, legal documents, or any sensitive document that requires an expert. Last updated: May 2026.
How to use this tool
- 01Paste the two textsIn the "Original text" box, paste the first version (for example the draft before editing). In the "Text to compare" box, paste the second version (after editing).
- 02Choose options (optional)Ignore case suits text that only had capitalization changes. Ignore whitespace suits code or text with different formatting. Ignore blank lines suits texts that differ only in how many empty lines they contain.
- 03Read the differencesThe summary shows how many lines were added, how many were removed, and how many stayed the same. In the view you see the actual differences: green lines with a + are added lines, red lines with a - are removed lines, and gray lines are unchanged.
- 04Copy the resultClicking "Copy result" copies the unified diff to memory. You can paste it into an email, a message, a document, or a version control system.
When is this useful?
- Compare a message before and after editingYou wrote a long email, a colleague edited it, and you want to see exactly what changed. Paste both versions and the tool shows you all the differences.
- Compare versions of a listYou have a list of names / addresses / products and you updated some of the items. The comparison shows which items were added to the list and which were removed.
- Check what changed in a code snippetYou copied a function into another file and changed something. Comparing the original version with the current one shows the changes you made clearly.
- Translation: compare a corrected translation versionYou got a translation back with corrections. Comparing the original translation with the corrected version shows where the translation changed and where it stayed.
- Track changes in an article draftA first version of an article against a version after editor feedback. The tool shows all the differences laid out line by line.
Examples
- A message that was lightly editedOriginal: "I wanted to update you about the project." versus "I wanted to update you about the new project." In this case one line was removed and one line was added, marked as a changed line.
- A list with an addition and a removalOriginal: apple / banana / cherry / date / elderberry. Changed: apple / banana / blueberry / date / fig. The tool shows a removed line (cherry), an updated line (banana -> blueberry depending on order), and an added line (fig).
- Ignore whitespace differencesOriginal: "a b c" versus "a b c". Without the option the comparison is marked as different. With "Ignore whitespace" the tool sees the line as identical.
- Ignore blank linesOriginal: "First paragraph\n\n\nSecond paragraph" versus "First paragraph\nSecond paragraph". With "Ignore blank lines" both versions are treated as identical.
Tips for a better result
- How the comparison algorithm worksThe tool uses the classic LCS (Longest Common Subsequence) algorithm. It finds the longest run of lines that appear in both texts in the same order, and then everything not in that run is marked as an added or removed line. This is deterministic: the same inputs always return the same result.
- When to use the "Ignore whitespace" optionWhen the texts look identical but the comparison finds a lot of differences, the difference might be in spaces, tabs, or lines that end with a space. Turning on the option collapses all those line variations into a single line for the comparison.
- Works with English, Hebrew, and codeThe tool compares lines as strings. It supports all texts: right-to-left text, left-to-right text, mixed, punctuation, emoji, and code with special characters. There is no automatic character normalization.
- Your texts stay with youBoth texts, the options, and the result are not saved to localStorage, not uploaded, and not sent to analytics. Refreshing the page resets everything.
How the comparison works
The tool splits both texts into lines (normalizing CRLF/CR to LF), builds a list of lines for each side, and runs a two-dimensional LCS algorithm. The result is a sequence of "edits": identical lines, added lines, and removed lines. An additional representation, the "side-by-side view", groups a removed line immediately followed by an added line into a "changed line" so you can see the change in place. The complexity is O(M*N) in time and memory, where M and N are the number of lines on each side. The tool limits each side to 5,000 lines for a good user experience; for larger files, command-line tools are recommended.
The normalization options
Ignore case (ignoreCase): compares lines while ignoring differences between A and a. Comparing "Hello" with "hello" returns identical. Ignore whitespace (ignoreWhitespace): collapses every run of spaces, tabs, or newlines into a single space, and trims leading and trailing spaces. Comparing "a b" with "a b" returns identical. Ignore blank lines (ignoreEmptyLines): removes blank lines / lines with only spaces from both sides before the comparison. All three options are independent and can be combined.
Unified view vs side-by-side view
The unified view shows all lines vertically with prefixes: " " for an unchanged line, "+" for an added line, "-" for a removed line. This is a standard format in the coding world and is easy to copy into an email / message. The side-by-side view shows two columns, left and right, with parallel lines aligned; the downside is that it can be narrow on mobile.
Cases where you should get someone else involved
For contracts, legal documents, complex code that needs a senior review, or sensitive documents: the tool shows textual differences only; it does not assess meaning, it is not a substitute for a lawyer reviewing the document, and it is not a substitute for a professional code review. Use it as a first display aid, then pass the result to the relevant expert.
Privacy
Everything happens in your browser. The texts, the options, and the result are not uploaded, not saved to localStorage or IndexedDB, and not sent to analytics. Minimal operational analytics measure general usage only: a page view, a first successful use of the tool, and a copy. No value, line, or text content is ever sent.
Frequently asked questions
What is a text diff checker?
A tool that compares two pieces of text line by line and shows what changed between the first version and the second version: which lines were added, which were removed, and which stayed the same.
How does the comparison work?
The tool splits each text into lines and runs an LCS (Longest Common Subsequence) algorithm that finds the longest run of identical lines in both texts in the same order. Anything not in that run is marked as an added line (present only on the right side) or a removed line (present only on the left side).
What is the difference between unified and side-by-side view?
The unified view shows all lines in one column with +/-/space prefixes. The side-by-side view shows two parallel columns. Unified is convenient to copy as a reply in an email or message; side-by-side is convenient for visual reading.
Does the tool support right-to-left text?
Yes. The tool compares the texts as strings in English, Hebrew, or mixed text. Right-to-left lines and left-to-right lines are handled the same way.
What is the maximum text size?
The tool handles up to 5,000 lines per side. For larger files, use a command-line tool (for example Unix diff or git diff).
Is the tool suitable for a legal comparison of a contract?
No. The tool shows textual differences only, not meaning. To review contracts, legal documents, or sensitive documents, consult a lawyer or the relevant expert.
Does the tool send my texts anywhere?
No. The entire comparison runs in your browser. Both texts, the options, and the result are not uploaded, not stored, and not sent to analytics.
Is the tool free?
Yes. The tool is free, with no signup, no account, and no reasonable usage limit.