Is my text uploaded for comparison?

No. The comparison runs in your browser, so you can safely diff configuration files, API responses or anything else internal. Nothing is transmitted or stored.

How does it decide which lines match?

It computes a longest common subsequence, the same general approach version control diffs use. That means inserted or deleted blocks are identified as such, rather than everything after the change being reported as different because the lines shifted position.

Can it show what changed within a line?

Yes. Lines that were modified rather than wholly added or removed get word-level highlighting, so on a long line with one altered value you see the specific word instead of just knowing the line differs.

Why are two lines that look identical marked as different?

Almost always invisible characters: trailing whitespace, a tab where the other has spaces, or Windows line endings against Unix ones. Turn on the whitespace option to confirm, and note that the tool normalises line endings so a pure CRLF-versus-LF difference is not reported as a change on every line.

Calculators & testers

Text Diff Checker — Compare Two Texts

Compare two texts side by side and see exactly what changed.

Ignore case

Ignore leading/trailing whitespace

Ignore blank lines

Original

Original text

Changed

Changed text

About this tool

A diff shows what changed between two versions of a text. Given the amount of time developers spend reading diffs in version control, it is easy to forget how often you need one for something that is not in a repository at all.

The usual cases: comparing two API responses to find the one field that differs, checking a config file against the version actually deployed, seeing what an editor changed in a draft, verifying that a migration produced identical output, or working out why two supposedly identical environment variable lists behave differently.

This tool compares line by line and shows the result side by side, with additions, removals and unchanged lines marked. It uses a longest-common-subsequence algorithm, which is the same approach version control tools take, so a block of inserted lines is reported as an insertion rather than shifting every following line and reporting the whole rest of the file as changed.

Word-level highlighting is available for lines that were modified rather than added or removed outright. On a long line where one value changed, knowing the line differs is not much help; seeing which word differs is the actual answer.

There are also options for the differences you usually do not care about. Ignoring case, ignoring leading and trailing whitespace, and ignoring blank lines will each remove a class of noise, which matters when comparing text that came from different sources and has picked up formatting differences that are not real differences.

How to use it

Paste the original text on the left and the changed text on the right.
Toggle case, whitespace or blank-line sensitivity if you want to ignore that kind of difference.
Read the side-by-side result, where changed lines are highlighted word by word.

Frequently asked questions

Is my text uploaded for comparison?: No. The comparison runs in your browser, so you can safely diff configuration files, API responses or anything else internal. Nothing is transmitted or stored.
How does it decide which lines match?: It computes a longest common subsequence, the same general approach version control diffs use. That means inserted or deleted blocks are identified as such, rather than everything after the change being reported as different because the lines shifted position.
Can it show what changed within a line?: Yes. Lines that were modified rather than wholly added or removed get word-level highlighting, so on a long line with one altered value you see the specific word instead of just knowing the line differs.
Why are two lines that look identical marked as different?: Almost always invisible characters: trailing whitespace, a tab where the other has spaces, or Windows line endings against Unix ones. Turn on the whitespace option to confirm, and note that the tool normalises line endings so a pure CRLF-versus-LF difference is not reported as a change on every line.