What is a text diff?

A text diff compares two versions of a document line by line and highlights what was added, removed, or modified. Diff algorithms power version control systems like Git, collaborative editing tools, and document review workflows. Understanding diffs is essential for tracking changes across any text-based content.

// JavaScript — compare two strings line by line
function diffLines(a, b) {
  const linesA = a.split("\n"), linesB = b.split("\n");
  return linesB.map((line, i) =>
    line === linesA[i] ? `  ${line}` : `+ ${line}`
  ).join("\n");
}

# Python — quick text diff
import difflib
diff = difflib.unified_diff(
    old.splitlines(), new.splitlines(),
    fromfile="original", tofile="modified", lineterm=""
)
print("\n".join(diff))

Common use cases

Text diffs are used to compare configuration files before and after changes, review edits in legal or technical documents, verify content migrations, and audit changes in CSV or log files. Writers and editors use them to see exactly what changed between drafts without reading the entire document.