About the Text Diff Checker

The Text Diff Checker compares two blocks of text line by line and highlights what changed between them. Added lines are highlighted green, removed lines red, and modified lines yellow, with a side-by-side view that lets you see exactly what was inserted, deleted, or altered. This is the same kind of visual diff that GitHub shows in pull requests, but it runs in your browser on any two text blocks you paste.

Diffs are essential for tracking changes in contracts, comparing two versions of a document, reviewing edits in a collaborative draft, or verifying that an automated transformation (like a find-and-replace) did what you expected. Without a diff tool, you have to read both versions carefully side by side and hope you spot every change — a process that breaks down on any document longer than a few paragraphs.

This tool performs a line-by-line comparison using a simple positional alignment: line 1 of the original is compared to line 1 of the modified, line 2 to line 2, and so on. This is fast and predictable but does not perform the more sophisticated longest-common-subsequence matching that Git uses. For most editing tasks the simple approach is clearer and easier to interpret.

How It Works

The tool splits both inputs on newlines and iterates through the resulting arrays up to the length of the longer one. For each position, it compares the original line and the modified line:

If both lines are identical, the row is marked as unchanged.
If the original line is empty and the modified is not, the row is marked as added (insertion).
If the modified line is empty and the original is not, the row is marked as removed (deletion).
If both lines exist but differ, the row is marked as modified (substitution).

Each row is rendered in an HTML table with color-coded backgrounds: green for unchanged and added, red for removed, yellow for modified. The original and modified text are shown side by side so you can see exactly what changed on each line.

The summary reports the count of each operation type (unchanged, added, removed, modified) so you can quickly assess the magnitude of changes — useful when reviewing whether a small edit accidentally touched many lines. The diff does not perform word-level highlighting within a line, so a modified line shows the entire line in yellow even if only one word changed.

Worked Examples

The default input shows a four-line original and a five-line modified version. The diff reveals: line 1 unchanged, line 2 modified (“dog” → “cat”), line 3 unchanged, line 4 unchanged, line 5 added (“A new line was added”). The summary reports 3 unchanged, 1 added, 0 removed, 1 modified — a small surgical edit to two locations.

If you paste two versions of a contract where one party changed a single payment clause from “Net 30” to “Net 60,” the diff will highlight that specific line in yellow while everything else stays green. This makes it trivial to verify that no other changes were snuck in — an important check during legal review.

For a larger change like rewriting a blog post, the diff will show many yellow and green rows. If most lines are yellow, the rewrite was substantial; if most are green with a few yellow, the edit was surgical. This helps editors decide whether to review the entire new version or focus on the changed sections.

When to Use This Tool

Reviewing edits made to a contract or legal document before signing.
Comparing two versions of a blog post or article to see what changed.
Verifying that an automated transformation (find-and-replace, case conversion) did what you expected.
Tracking changes in configuration files when reviewing server or app updates.
Comparing student essay drafts to see how the work evolved.
Auditing copy edits in marketing materials before final approval.
Detecting unauthorized changes in shared documents after collaborative editing.

Limitations & Disclaimer

This tool performs positional (line-by-line) comparison rather than longest-common-subsequence alignment, so insertions or deletions in the middle of a document will cause all subsequent lines to appear as modified even if they were unchanged. Whitespace-only differences are detected by default (no option to ignore). Word-level changes within a modified line are not highlighted — the entire line is marked. Very large inputs (over ~10,000 lines) may cause browser performance issues. The tool does not perform three-way merge or conflict resolution. See our disclaimer for full terms.

Frequently Asked Questions

How is this different from a Git diff?

Git uses the Myers diff algorithm, which finds the longest common subsequence between two texts and aligns them intelligently even when lines are inserted or deleted in the middle. This tool uses simpler positional alignment: line 1 is compared to line 1, line 2 to line 2, and so on. Git's approach is smarter for code; ours is clearer for prose where you typically edit in place.

Can I compare more than two texts?

Not in a single comparison. To compare three versions, run two comparisons: original vs. middle, then middle vs. final. For three-way merges (like Git's <code>git merge</code>), use a dedicated merge tool that understands conflict resolution.

Does the diff highlight word-level changes within a line?

No. A modified line is highlighted in yellow as a whole, even if only one word changed. For word-level highlighting, use a dedicated word-diff tool or a code editor's diff view (VS Code, IntelliJ) which perform intra-line diffing.

What about whitespace-only changes?

By default, whitespace matters — a line with a trailing space differs from the same line without. Most editors can toggle “ignore whitespace” in diff view; this tool does not offer that option. To compare ignoring whitespace, normalize both inputs first (e.g., trim trailing spaces, collapse multiple spaces) using the Find and Replace tool.

Is there a limit on input size?

There is no hard limit, but very large inputs (over 10,000 lines) will produce a very long results table that may slow the browser. For comparing large files, use a command-line tool like <code>diff</code> or <code>git diff --no-index</code> instead.

Is my text uploaded anywhere?

No. The comparison happens entirely in your browser using JavaScript. Your contracts, drafts, and confidential documents never leave your device, which makes this tool safe for sensitive content.

Last updated: July 21, 2026 · Author: HT99 Tools Editorial Team · Reviewed by: HT99 Tools Editorial Team