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Diff results will appear here
Paste two texts above and click Compare// highlight word-level and line-level changes between two texts
Compare two texts side by side with word-level and line-level diff highlighting. Instantly spot insertions, deletions, and changes. Free, browser-based, no upload required.
Diff results will appear here
Paste two texts above and click CompareEnter your original text on the left and the modified version on the right.
Choose view mode, toggle word-level diff, case sensitivity, and whitespace handling.
Click Compare to highlight changes. Copy or download the diff result.
The Text Diff Highlighter computes the differences between two blocks of text using a line-level LCS (Longest Common Subsequence) algorithm, with an optional word-level pass for fine-grained highlighting within changed lines. All processing happens locally in your browser โ nothing is sent to any server.
It uses a Longest Common Subsequence (LCS) algorithm at the line level to determine which lines were added, removed, or kept. For word-level diff, the same LCS approach is applied within each changed line to highlight the specific words that differ.
No. All diffing is done entirely in your browser using JavaScript. Your text never leaves your device, making this tool safe for sensitive or confidential content.
The similarity percentage is calculated as (unchanged lines / total lines) ร 100. A score of 100% means the texts are identical; 0% means no lines are shared at all.
Yes. While this tool works on plain text, you can paste code directly into either panel. For syntax-highlighted code diffs, check our Code Diff Viewer tool.
When enabled, leading and trailing spaces on each line are trimmed before comparison. This prevents indentation changes from being flagged as meaningful differences, which is useful when comparing code that has been reformatted.
Side by Side shows the original and modified texts in two columns with changes aligned across rows. Unified view shows all lines in a single column, with added lines marked in green and removed lines in red โ similar to a Git diff output.
There is no hard limit enforced by the tool. However, very large texts (over 10,000 lines) may cause a short delay while the LCS algorithm processes, as it runs in your browser.
Yes. Click the "Download" button to save a plain text file containing the unified diff output, which you can share or archive.
A text diff highlighter is a tool that takes two versions of a text and visually marks every addition, deletion, and unchanged segment. Unlike a simple "find in page" or manual side-by-side reading, a diff tool computes the structural difference algorithmically โ meaning it finds the optimal set of changes required to transform one text into the other.
This is indispensable for developers reviewing pull requests, writers comparing document drafts, legal teams tracking contract revisions, and data engineers auditing configuration changes. Our Text Diff Highlighter brings that power to any browser, with zero setup and zero data transmission.
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The Longest Common Subsequence (LCS) algorithm is the foundation of most text diff tools, including Unix's diff command and Git's diff engine. Given two sequences of lines, LCS finds the longest ordered list of lines that appear in both โ without reordering. Lines outside that common sequence are flagged as either removed (from the original) or added (to the modified version).
The complexity of a naive LCS is O(nรm), where n and m are the line counts of each text. For typical document sizes this is fast. Our implementation uses an optimized patience diff approach that performs especially well on structured text like source code, where many lines are identical boilerplate.
Line-level diffing is coarse: if even one word changes in a paragraph, the entire line is marked as changed. This is sufficient when you want a quick overview โ "which paragraphs changed?" โ but insufficient when you need precision.
Word-level diffing goes deeper. Once two lines are identified as a changed pair (one removed, one added), the tool runs a second LCS pass over the individual words within those lines. The result is that only the specific words that differ are highlighted, while unchanged words remain neutral. This is what makes our tool especially useful for proofreading, translation review, and contract comparison.
Side by Side presents the original text on the left and the modified text on the right, with corresponding changed lines aligned horizontally. This is the most intuitive format for human readers because you can see context on both sides simultaneously.
Unified view is modelled after the standard diff -u output used in Git. Removed lines appear in red with a โ prefix; added lines appear in green with a + prefix; unchanged lines are shown without decoration. This format is more compact and is ideal for generating a diff to paste into a commit message, bug report, or changelog.
.env, nginx.conf, or Kubernetes YAML files across environments. This tool highlights exactly which keys or values changed.The Ignore Case option makes the comparison case-insensitive before computing the diff. This is useful when comparing text that may have been transformed by a text processor that normalised capitalisation, or when comparing HTML attributes that might be upper or lower case.
The Ignore Whitespace option trims leading and trailing spaces from each line before comparison. This prevents reindentation โ a common result of code formatters like Prettier or Black โ from flooding the diff with irrelevant changes, letting you focus on the actual logic changes.
Because the entire diff computation runs in your browser, no text is ever transmitted over the network. This makes the tool suitable for comparing sensitive content: source code containing credentials, legal documents under NDA, personal health records, or private correspondence. There are no accounts, no logs, and no cookies beyond what is strictly necessary for the page to function.
The Download button exports the unified diff as a .txt file. This file follows the standard unified diff format and can be applied as a patch using the Unix patch command, shared as an attachment, or archived for audit purposes. The Copy button places the same content on your clipboard for quick pasting into emails, Slack messages, or issue tracker comments.