Text Diff Checker

What is the Text Diff Checker?

The Text Diff Checker compares two blocks of text and highlights what was added, removed, and left unchanged. It is the same idea as a version-control diff, applied to any text you paste in.

Comparing two similar documents by eye is unreliable, the differences that matter are often a single character in a long line, and human attention is poor at that kind of scanning. A diff algorithm finds the longest common subsequence between the two texts and reports everything else as a change.

The result is presented as additions and deletions. A modified line is generally represented as a deletion followed by an addition, since most diff algorithms operate on whole lines rather than tracking edits within them.

Granularity matters. A line-level diff is right for code and configuration; a word-level or character-level diff is better for prose, where a line may be a whole paragraph and a one-word change would otherwise mark the entire paragraph as rewritten.

How to use the Text Diff Checker

1. Paste the original text. Put the earlier or reference version into the left pane.
2. Paste the version to compare. Put the newer or candidate version into the right pane.
3. Review the highlighted differences. Additions and deletions are colour-coded, with unchanged content shown for context.
4. Adjust options as needed. Ignoring whitespace or case is useful when those differences are not meaningful for your comparison.

Worked examples

--- Original            +++ Modified
host: localhost         host: localhost
port: 5432              port: 5432
debug: true             debug: false
timeout: 30             timeout: 60
                        retries: 3

  host: localhost
  port: 5432
- debug: true
+ debug: false
- timeout: 30
+ timeout: 60
+ retries: 3

A: const rate = 0.15;
B: const rate = 0.l5;

- const rate = 0.15;
+ const rate = 0.l5;

The digit 1 was replaced with a lowercase L.

Common use cases

• Comparing configuration across environments. Diffing staging against production config is often the fastest way to explain an environment-specific bug.
• Reviewing document revisions. Seeing exactly what changed between two drafts is quicker than rereading both.
• Verifying copied data. Confirming that a transferred or transformed file matches the original.
• Checking API responses. Diffing responses from two versions of an endpoint reveals unintended contract changes.

Features and limitations

• Side-by-side comparison with colour-coded additions and deletions.
• Options to ignore whitespace or case differences.
• Handles multi-line documents of substantial size.
• Works with any plain text, including code, configuration, CSV, and prose.
• Line-oriented by default, so a small edit within a long line marks the whole line as changed.

Frequently asked questions