Code Difference Comparison Tool

Diff two code or text blocks line by line with unified +/- output and change counts.

Compare two code blocks line by line instantly. Free online code diff tool with unified +/- output and added/removed statistics.

About Code Diff

Diff two code or text blocks line by line with unified +/- output and change counts.

Paste the original and modified text. The tool aligns them with a longest-common-subsequence pass, then walks the alignment emitting context lines, additions (+), and deletions (−) with counts — the same shape as unified diffs from git.

Inputs cap at 500 lines per side to keep the quadratic pass instant in the browser; toggle whitespace-insensitivity for formatting-only comparisons. Everything runs locally.

Where it is used

Reviewing config changes, spotting what broke between deploys, comparing API responses, and checking student submissions.

How to use the Code Diff

  1. Original Code — enter the value (e.g. const x = 1;).
  2. Modified Code — enter the value (e.g. const x = 2;).
  3. Ignore Leading/Trailing Whitespace — enter the value.
  4. Calculate — press the Calculate button to see the result instantly above.

Formula

Longest-common-subsequence DP over lines → same/add/delete walk.

Examples

Example

originalText:const x = 1;
modifiedText:const x = 2;
ignoreWhitespace:false
Result: - const x = 1; / + const x = 2;

Frequently Asked Questions

How is this different from git diff?
Same output shape, zero setup: paste two snippets instead of committing. For repos and history, git remains the right tool.
Why cap at 500 lines?
LCS is quadratic in input size; the cap keeps large pastes instant instead of freezing the tab. Split bigger files into hunks.
Does it detect moved blocks?
Partially — a move shows as a delete plus an add. True move detection needs a fancier (and slower) algorithm.
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