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Text Diff Checker
A text diff checker compares two blocks of text and highlights exactly what changed between them, line by line, so a single altered character is never missed in a wall of otherwise identical content. It is the fastest way to confirm what an edit actually did, whether the task is reviewing a rewritten meta description, checking a redirect map against last month’s version, or spotting the one line a content brief gained between drafts.
This tool runs a real longest common subsequence diff in your browser, marking added lines in green, removed lines in red, and unchanged lines in plain text, with live counts of each. It is free, needs no sign-up, and nothing you paste is uploaded anywhere.
🔒 Private: everything runs in your browser. Nothing you paste is uploaded.
How to use the text diff checker
Paste the original text on the left and the changed text on the right. The comparison updates as you type, or click Compare to run it on demand, and you can switch between a side-by-side and a unified view.
Read the colours and the change counts
Every line is classified into one of three states. Green lines were added in the changed version, red lines were removed from the original, and plain lines are identical in both. The status pills above the result total each category, so a quick glance answers how much really moved: a long document with only two green and one red line had a tiny edit, even if it looks daunting. The side-by-side view pairs each removed line with the line that replaced it, while the unified view stacks everything in one column for copying or scanning top to bottom.
Use the ignore toggles to cut through noise
Not every difference is meaningful. Turn on ignore leading and trailing whitespace when indentation or stray trailing spaces are flagging lines that are really the same. Turn on ignore case when a capitalisation change should not count as an edit, which is common when comparing URLs, slugs, or normalised keyword lists. The stronger ignore all whitespace option collapses every space and tab before comparing, useful for reflowed paragraphs. The displayed text always stays exactly as pasted; the toggles only change how lines are matched, not what you see.
Why a real LCS diff beats a naive line-by-line check
A naive comparison checks line 1 against line 1, line 2 against line 2, and so on, which falls apart the moment a single line is inserted near the top: every line after it shifts and reports as changed. This tool uses a longest common subsequence algorithm, the same approach behind version-control diffs, to find the largest set of lines that appear in both texts in the same order. The result is the minimal, human-sensible set of additions and removals, so an inserted paragraph shows as one green block rather than dozens of false changes.
Text diff checker frequently asked questions
Q1How does this text diff checker decide what changed?
It splits both texts into lines and runs a longest common subsequence algorithm, the same family of diff used by Git and other version-control tools. That finds the largest set of lines shared by both versions in order, then marks everything else as added or removed. The result is the smallest sensible set of changes, so an inserted line shows once rather than shifting and flagging every line below it.
Q2Is my text uploaded or stored anywhere?
No. The entire comparison runs in your browser with client-side JavaScript, and neither block of text is sent to a server, logged, or saved. The tool keeps working even with the network disconnected once the page has loaded, which makes it safe for confidential drafts, internal redirect maps, or anything you would rather not paste into an online service.
Q3What is the difference between the side-by-side and unified views?
Side-by-side places the original on the left and the changed version on the right, aligning each removed line with the line that replaced it, which is best for reviewing edits visually. Unified stacks both into a single column with plus and minus markers, the format used in code review and patches, which is easier to copy or scan top to bottom on a narrow screen.
Q4Can it ignore whitespace and capitalisation differences?
Yes. Toggle ignore leading and trailing whitespace to skip indentation and trailing-space noise, ignore case to treat capitalisation changes as identical, and ignore all whitespace to collapse every space and tab before comparing. These affect only how lines are matched. The highlighted output always shows your text exactly as pasted, so nothing is silently rewritten.
Q5Does it compare word-by-word or line-by-line?
This tool compares at the line level, which is the right granularity for most SEO and content tasks: meta tags, redirect maps, lists, briefs, and configuration files are naturally line-based. When a line changes, it appears as one removed line and one added line side by side, so you can read both versions together and see precisely which line moved without word-level noise.
