Text Diff Checker
Put two drafts side by side and see precisely what changed between them.
Lines with a green bar were added, lines with a red bar were removed.
What the text Diff Checker does
A diff checker answers a specific question: what actually changed between these two versions? Paste the original on the left and the revision on the right, and the tool aligns the two texts line by line and marks each line as added, removed or unchanged.
The alignment uses a longest-common-subsequence algorithm, the same approach behind
git diff and most code review tools. Rather than comparing line 1 to line 1 and line 2
to line 2 — which falls apart the moment you insert a sentence near the top — it finds
the longest run of lines the two texts genuinely share, then reports everything else as an
insertion or a deletion. That is why adding a paragraph in the middle of a document shows up as one
added block instead of marking every subsequent line as changed.
Three options tune the comparison. Ignoring leading and trailing whitespace stops indentation changes from swamping the result, which matters when you are comparing text copied out of different editors. Ignoring letter case is useful for comparing content where capitalisation is not meaningful. Hiding unchanged lines collapses the output to just the edits, which makes long documents with a handful of changes far easier to scan.
It works on anything line-based: contract drafts, configuration files, CSV exports, translated copy, or two versions of a blog post. Because it runs locally, you can safely compare confidential documents that you would not paste into a hosted diff service.
How to use it
- Paste the original version into the left box and the newer version into the right box.
- Adjust the ignore options if formatting noise is getting in the way of the real changes.
- Read the coloured output: green lines with a plus were added, red lines with a minus were removed.
A worked example
Comparing two versions of a customer email, the tool reports two removals and three additions:
Thank you for your order placed on 3 March.
− We expect to ship within five working days.
+ We expect to ship within two working days.
+ Your tracking number will follow by email.
Please contact support with any questions.
− The team
+ The Tooltrusty teamNotice that the shipping line appears as both a removal and an addition. Line-based diffs do not report edits within a line — a changed line is modelled as the old one going away and a new one arriving. That is standard behaviour and it is why the unchanged count only covers lines that matched exactly.
Frequently asked questions
Does it highlight changes within a single line?
No — this is a line-level diff. A line with one word changed shows as a removal plus an addition. For prose, that is usually easier to read than character-level highlighting, and it matches how version control systems report changes.
Can I compare two files rather than pasting text?
Open each file in a text editor and paste the contents in. Adding a file picker would mean reading files that are often confidential, and pasting keeps the flow explicit about what is being compared.
Why does it say the texts are too large to compare?
The algorithm builds a comparison grid whose size is the product of the two line counts, so two 2,000-line documents are fine but two 100,000-line files would exhaust memory. Compare a section at a time if you hit the limit.
Is anything I paste stored or transmitted?
No. The comparison runs in JavaScript in this tab. Nothing is sent to a server, which is the point — contract drafts and internal documents are exactly the sort of thing people diff, and exactly the sort of thing that should not be uploaded.