What this diff checker does
Two versions of the same document drift apart quietly: a contract redrafted, a product list updated, a chapter edited by two people in two places, a configuration file copied and changed. Reading both versions side by side and hoping to spot every difference is slow and unreliable — especially the dangerous kind of change, the line that is missing, which leaves nothing on the page to catch your eye. Paste the earlier version on the left and the later version on the right, press Compare, and this tool does the line-by-line audit for you. Every line that exists only in the original is listed with a − marker; every line that exists only in the revised text is listed with a + marker; and the summary counts how many lines fell into each group and how many were unchanged, so you know at a glance whether you are looking at a light touch-up or a substantial rewrite.
How to read the results — and how the comparison works
The comparison is made whole lines at a time. A line counts as unchanged only if the identical line appears somewhere in the other text. That produces one behavior to understand: an edited line shows up twice — once as a − line (the old wording) and once as a + line (the new wording), because the old line is indeed gone and the new one is indeed new. When you see a − and a + that look like near-twins, that is an edit; a − with no twin is a deletion, and a + with no twin is an addition. Two more consequences follow from the line-based approach. First, the tool does not track where a line moved — a paragraph relocated within the document is still present in both, so it correctly reports as unchanged. Second, matching is exact, so a line that differs only by a trailing space or a capital letter registers as changed, which is what you want when the exercise is auditing rather than skimming.
If what you need is to remove repetition rather than find it, the Remove Duplicate Lines tool strips repeated lines from a single text; and if you want to know how much text changed in size, the Character Counter's counts on each version give you the before-and-after numbers.
Typical uses
- Proofreading edits: confirm that the changes you asked an editor (or an AI assistant) to make are the only changes that happened.
- Lists and records: compare this month's member, product or inventory list against last month's to find additions and removals instantly.
- Code and configuration: check what actually changed between two versions of a script, a settings file or a set of instructions before the new one replaces the old.
- Documents and terms: spot what was added or quietly removed when a policy, agreement or set of terms is reissued.
Frequently asked questions
A line I only edited slightly shows as both removed and added. Why?
Because the comparison works on whole lines: the old wording no longer exists in the revised text, and the new wording did not exist in the original. A −/+ pair that look nearly identical is one edited line — read them together.
Does it matter if lines are in a different order?
No. The checker tests whether each line exists in the other text, not where it sits, so reordering lines or moving a paragraph is not reported as a change.
Can it compare documents character by character?
This is a line-level checker, designed for lists, drafts and files where the line is the natural unit. It will not highlight which word changed inside an edited line — the − and + pair shows you the whole before and after lines to compare yourself.
Is my text uploaded or saved?
No. Both texts are compared in your browser, on your device — which makes this safe for drafts, lists and documents you would not paste into a stranger's server.
Private by design: this checker runs entirely in your browser. Both texts you paste are compared on your device and are never uploaded, stored or shared.