Diff Checker

How do I compare two texts to find the differences?

1. Paste the original version into the Input box.
2. Paste the new version into the Changed text box.
3. Choose Compare by: Lines for documents and code, Words for prose edits, Characters for small typo-level changes.
4. Tick Ignore whitespace changes to skip differences in spaces, tabs and indentation.
5. Click Compare and read the output: removed content starts with "- ", added content with "+ ", and the counts of additions and removals are shown.
6. Click Copy output to paste the diff into an email, ticket or review comment.

The diff checker runs a standard longest-common-subsequence comparison, the same approach behind git diff and the track changes view in Word, and reports only what differs. Unchanged content is left unmarked, removed content gets a leading "- " and added content a leading "+ ", so a line that was edited shows as one removal followed by one addition. The counts of additions and removals give you a quick sense of how big the change is before you read it.

Compare by decides the unit of comparison. Lines is the right choice for code, CSV exports, configuration files and anything where each line is a record; it is also fastest on long inputs. Words suits prose, because a single reworded sentence shows as a few changed words rather than a whole replaced paragraph. Characters is the most precise and is useful for spotting a changed digit in a reference number, a swapped letter in a name or a stray full stop, but on long texts the output becomes noisy.

Ignore whitespace changes treats runs of spaces and tabs as equivalent and ignores leading and trailing space on each line, so reformatting, re-indenting and different line endings do not show up as changes. It is what you want when comparing a file saved on Windows with one saved on a Mac, or a document pasted from two different editors.

Typical jobs: checking what a colleague changed in a contract clause, confirming a supplier's revised terms match what was agreed, comparing two exports of the same report, reviewing edits to a web page's copy, or seeing exactly what a find-and-replace did. Both texts stay inside your browser tab as plain JavaScript, never transmitted or stored, so confidential drafts and legal documents are safe to compare. Texts of several thousand lines compare in well under a second. If you need JSON compared, run both versions through the JSON Formatter with Sort keys on first so key order does not create false differences.

How it works: this tool uses plain JavaScript running in your browser tab. No server is involved, so Kilnfile never sees your file. Last reviewed 20 September 2026.

Frequently asked questions