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 is line-by-line and position-by-position: line one is compared with line one, line two with line two, and so on.

What it does not do is worth stating plainly. It does not highlight which words or characters changed within a line, does not align shifted blocks intelligently, 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 caused by the positional matching. Because each line is compared with the line at the same position, inserting or deleting a single line near the top can make every line below it report as changed, since each one is now lined up against a different counterpart. If your diff looks far larger than expected, this misalignment is usually why, and it does not mean the tool is wrong, only that it is comparing by position rather than finding the smallest set of edits.

The second pitfall is the separator itself. If your own text contains a line of three or more dashes, that line will be read as the divider and split your input in an unintended place. If you forget the separator entirely, everything is treated as the old version and the new side is empty, so every line shows as removed. Make sure exactly one --- line sits between the two versions.

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 a known edit is missing or the diff seems unexpectedly large, suspect a line insertion that shifted the alignment and re-check by adding or removing a blank line so the unchanged sections line up again.

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.