The Diff Checker compares two texts or two blocks of code and shows exactly what changed, line by line and character by character. It runs entirely in your browser: nothing you paste here is uploaded, stored online, or sent to any server. Compare two versions of a document, a config file, a code snippet or a log excerpt and take the results with you as a patch file, a CSV change list or a PDF.

Choose a split view for a clean two-column comparison or a unified view for the single-column style familiar from Git. Switch the inner-line precision between Smart, Word and Char at any time, highlight code syntax, and merge individual changed lines across with a single click.

Enter an original text on the left side and a changed version on the right side, then press Compare. The tool builds a diff in your browser and colors every difference. Deep-red lines exist only in the original and were removed. Deep-green lines exist only in the changed text and were added. Lines that appear on both sides but contain changes are marked in the corresponding characters — a delete mark on the left and an insert mark on the right. Use the Prev and Next buttons to jump between changes, the arrows between the two columns to pull a line across, and the exports under the result to save or print your work.

Split and unified views: A two-column split view shows both texts side by side. The unified view collapses the same comparison into one column, exactly like a Git review, with a − mark on removed lines and a + mark on added lines. Switching views does not re-compare anything.

Smart, Word or Char precision: Smart (default) highlights single characters when that reads clearly, and whole words when the change is longer. Compare count: 3 against count: 5 and only the differing digit is marked. Word mode always marks whole words, so the sentence the quick brown fox turning into the slow brown fox shows the single word marked and the rest untouched. You can change the level at any time without re-comparing.

Syntax highlighting: Pick HTML/XML, CSS, JavaScript, JSON, C-like languages, Markdown, Python, SQL or YAML to color the code, or let auto-detect guess the language from your first press of Compare. Highlighting works on top of the diff marks, so colored tokens and red/green change marks appear together.

Ignore rules: Expand Ignore rules and choose what should not count as a difference. Ignore case, trim leading and trailing whitespace, hide whitespace-only changes, skip quotation marks or dashes, or add your own rules (one per line) for anything that changes on every run, such as build numbers. The rules only change how lines are matched; the raw text you typed stays in the editors and in the results.

Hide unchanged lines: Long files collapse into short hunks with three lines of context around each change. Each collapsed block reads “N unchanged lines hidden” and expands with one click.

Merge arrows: Every change row has arrows between the columns. The right arrow takes the original line over to the changed text; the left arrow takes the changed line back over to the original. Surplus lines of a replaced block move across with a single arrow each. The diff recalculates immediately after every merge.

Real-time editing: The editors stay visible after the first comparison. Edit either side and the diff updates about a third of a second after you stop typing, keeping your scroll position, view mode and highlighting options.

Copy, download, export: Below the result you can copy the diff as a plus/minus style patch, download it as diff.txt, export the change list as diff.csv (opens directly in Excel), or use Print / PDF to save the full comparison as a PDF from the print dialog.

Recents: Each manual comparison is stored locally in your browser (up to 8 entries) so you can restore a previous pair of texts with one click. Recent entries never leave your machine and can be deleted individually.

Keyboard shortcuts: Alt+Left and Alt+Right jump to the previous and next change, Alt+1 and Alt+2 switch between split and unified view, and Alt+Enter re-runs the comparison.

1. Enter your texts: Paste or type the original text into the left editor and the changed version into the right editor. You can also open a file with the tab above each editor or drag a file onto it.

2. Press Compare: The diff appears below the editors with a stat bar: a red − badge for removed lines, a green + badge for added lines, and the line, word and character counts of both texts.

3. Adjust the view: Use the controls above the result to switch between split and unified view, change the inner-line precision, turn syntax highlighting on or off, or collapse unchanged lines. Every switch takes effect immediately without re-comparing.

4. Work with the diff: Jump between changes with Prev/Next, and merge single lines across with the arrows between the columns. Editing either editor updates the diff automatically.

5. Take the result with you: Copy the patch to the clipboard, download it as a text file, export the change list as CSV, or print the comparison as a PDF. Nothing is uploaded at any point.

FAQ 1: Is my text uploaded anywhere?
Answer: No. Everything — the diff engine, syntax highlighting, exports and the saved recents — runs inside your browser. Nothing is sent to or stored on a server. Recents are saved only in your own browser storage (localStorage) and never leave your computer.

FAQ 2: Is there a limit on text size?
Answer: There is no hard limit. The comparison happens locally, so very large files are only as slow as your browser makes them; keeping each side within a few thousand lines stays snappy even on modest devices. Files up to a few megabytes work fine on a modern desktop.

FAQ 3: What do the − and + badges mean?
Answer: The bar above the diff counts every line that the comparison touched. −N is how many lines exist only in the original (removed), +N is how many lines exist only in the changed text (added). Lines changed on both sides count in both numbers. The badges also list how many lines, words and characters each side has.

FAQ 4: Is this the same tool as the Simple Diff Checker?
Answer: No, they are separate tools. The Simple Diff Checker does a fast line-by-line comparison, which is enough for quick text checks. This Diff Checker is the advanced version: inner-line precision (word and character), unified view, syntax highlighting, ignore rules, merge arrows, hide-unchanged collapse, CSV and PDF exports and a recents list. Use whichever suits the job — both are free and private.

FAQ 5: What exactly does one merge arrow do?
Answer: Pressing an arrow merges only that one row. On a changed pair, the right arrow makes the changed side use the original's line for that row, and the left arrow makes the original side use the changed line. On a surplus row (a line that exists on only one side), the single arrow inserts that line into the other text. It never rewrites your editors wholesale — you can still edit them afterwards and the diff updates.

FAQ 6: How do the ignore options differ from each other?
Answer: Ignore case folds capitals and lowercase together. Trim whitespace ignores spaces at the start and end of lines. Hide whitespace changes also ignores different spaces or tabs inside a line. Ignore quotations and Ignore dashes remove quote and dash characters from the comparison. Custom ignore rules go further and skip text you specify (for example a build number) anywhere in a line. All of them change only the comparison; the raw text in your editors always stays exactly as you typed it.