Compare two text or code blocks 100% locally in your browser with line-level and word-level inline diffing, side-by-side and unified views, and zero server uploads.
| # | Original (A) | # | Modified (B) |
|---|---|---|---|
| 1 | =Project: PeekAndDo Utilities | 1 | =Project: PeekAndDo Utilities |
| 2 | −Payment is due within 30 calendar days of invoice date. | 2 | +Payment is due within 15 business days of invoice receipt. |
| 3 | −Server port: 8080 | 3 | +Server port: 9090 |
| 4 | =Mode: staging | 4 | =Mode: staging |
| 5 | +Strict Privacy: enabled |
| A# | B# | Status | Line Content |
|---|
A text diff checker computes the Shortest Edit Script (SES) and Longest Common Subsequence (LCS) between an Original text (Panel A) and a Modified text (Panel B) to identify added (+), removed (−), and unchanged (=) lines and inline word edits—100% locally inside your browser without uploading sensitive content to any server.
First, Windows CRLF (\r\n) and legacy CR (\r) line endings are normalized to standard LF (\n). Common unchanged prefix and suffix lines are stripped in O(N) time, and dynamic programming Longest Common Subsequence (LCS) alignment is computed across the changed window. Contiguous removed and added line blocks are paired so a secondary token-level LCS pass can highlight exact inline word insertions (<ins>) and deletions (<del>).
Original (A): 'Payment is due within 30 calendar days of invoice date.' vs. Modified (B): 'Payment is due within 15 business days of invoice receipt.'
1 modified line pair detected: '30 calendar' and 'date.' marked as removed (− <del>), '15 business' and 'receipt.' marked as added (+ <ins>).
Comparing two JSON/YAML snippets where one uses 2-space indentation and the other uses 4-space indentation, plus one changed port number (8080 → 9090).
With 'Ignore Whitespace' enabled, all indentation-only lines are marked Unchanged (=), isolating only the single line where 8080 changed to 9090.
Yes. PeekAndDo's Private Text Diff Checker executes 100% locally inside your web browser using client-side JavaScript. Your text never leaves your device, is never transmitted to any API or server, and is never persisted in localStorage, sessionStorage, or cookies.
Diff tools solve the Longest Common Subsequence (LCS) problem—closely related to Eugene Myers' O(ND) difference algorithm (1986). By finding the longest sequence of lines (and words within modified lines) that appear in both Panel A and Panel B in the same relative order, the engine isolates only the minimal insertions (+) and deletions (−) required to transform Text A into Text B.
Side-by-Side (Split) View places Original lines on the left and Modified lines on the right so you can read corresponding revisions across two columns. Unified View stacks removed lines (−) and added lines (+) in a single vertical stream—the same format used by `git diff` and standard software patch files.
Often one text uses Windows line endings (CRLF, `\r\n`) while the other uses Unix/macOS line endings (LF, `\n`), or one has trailing spaces at the end of lines. PeekAndDo automatically normalizes `\r\n` to `\n` and provides an 'Ignore Whitespace' toggle so formatting noise does not obscure real content changes.