Text Diff Checker

The Text Diff Checker compares two versions of plain text and shows you, line by line, which lines stayed the same, which were removed, and which were added. It suits the small, frequent moments where you just need to see what changed between two blocks of text without opening a full version-control tool: comparing a draft of a paragraph against an edited copy, checking a configuration snippet against a known-good one, or spotting the single altered line in a list someone pasted back to you.

In day-to-day developer and admin work it helps with things like diffing two .env files, two short config blocks, a before-and-after log excerpt, or two copies of a CSV header row. For writers and office users it answers the practical question "what did the editor actually change?" when track-changes was not used. Students and reviewers can line up two answers, two citations, or two list versions side by side and read the differences directly.

It is deliberately a quick checker, not a merge tool or a code review platform. Reach for it when both versions already exist as text you can paste, the content is line-oriented, and you want a fast visual answer rather than a saved, shareable comparison history.

The flow is paste-based and runs entirely in your browser. You put both versions into a single input area, separated by a line containing three or more dashes (---). Everything above that separator is treated as the old (left) version and everything below it as the new (right) version. Press Run, and the result appears in the output panel, which you can Copy to the clipboard or Download as a text file.

The output uses simple prefixes you can scan at a glance: two leading spaces mean the line is unchanged, a leading minus (-) marks a line present only in the old version, and a leading plus (+) marks a line present only in the new version. The comparison finds the longest run of lines the two versions share and marks everything else, so inserting one line near the top marks only that line as added and the rest still shows as unchanged.

What it does not do is worth stating plainly. It does not highlight which words or characters changed within a line, does not detect moved blocks, does not read uploaded files, and does not produce a unified patch or colour-coded GitHub-style view. It compares the two pasted sides exactly as written, including trailing spaces and case.

The most common surprise is reflowed text. A line diff compares whole lines, so a paragraph whose line breaks moved shows every affected line as a - and + pair even if only one word changed. A block that was moved shows as a removal in one place and an addition in another, because a line diff has no notion of moving.

The second pitfall is the separator itself. Only the first line of three or more dashes is used as the divider, and later ones count as ordinary content, but if your original text contains such a line it will be taken as the divider, so change it temporarily. If you forget the separator, the tool asks for it instead of comparing.

Finally, the match is exact. A trailing space, a different capital letter, a tab versus spaces, or Windows versus Unix line endings will each register as a difference even when the visible text looks identical. Whitespace-only and case-only changes are reported the same as any other change.

Before relying on the result, confirm the basics: that a single --- line cleanly separates the two versions, that the old text is above it and the new text below, and that the two sides actually have the line counts you expect. Skim the output for whether the changes you knew about appear as matching minus and plus lines; if the diff seems unexpectedly large, look for a reflowed paragraph or different line endings rather than a real change on every line.

When a difference looks suspicious, copy the two lines in question and compare them closely for invisible causes, trailing spaces, mixed tabs and spaces, or a capitalisation change. Because the tool does not point inside a line, a quick manual read of the marked lines is the reliable way to see exactly what moved.

For anything official, financial, legal, or contractual, treat this as a first-pass visual aid rather than a verdict. Verify critical differences against the authoritative source documents directly, and have a second person confirm any change that affects amounts, names, dates, or obligations before acting on it.