Compare two texts or code snippets side-by-side. Highlights added, removed, and unchanged lines instantly.
Diff Checker compares two blocks of text side-by-side and highlights exactly what changed between them — lines that were added, removed, or modified. Paste an original version on the left and a revised version on the right, and the tool aligns matching lines and marks the differences inline so you can spot every change at a glance.
Developers use it to review edits before committing, compare two versions of a config file, JSON payload, log output, or SQL query, and confirm that a copy-paste or refactor didn't introduce unexpected changes. Writers and analysts use it to compare drafts, CSV exports, or API responses. Everything runs in your browser, so no text ever leaves your machine.
The tool performs a line-based diff using a longest-common-subsequence (LCS) algorithm, the same approach behind Unix diff and Git. It finds the longest sequence of lines that appear in both texts in the same order, treats those as the unchanged baseline, and then marks every line that isn't part of that sequence as either a deletion (present only in the original) or an addition (present only in the revised text). A line that changed is shown as a deletion of the old line paired with an addition of the new one.
Comparison is done per line and is whitespace- and case-sensitive, so 'Value' and 'value', or a trailing space, register as differences. This precision is what makes it reliable for code and structured data, where a single character can matter. For very large inputs the LCS computation grows with the product of the line counts of both sides, so extremely long files may take a moment to render.
Because the algorithm aligns on matching lines rather than character positions, inserting a single line near the top does not cascade into every line below being flagged — the tool re-syncs on the next common line, keeping the output readable.
Yes, it is completely free with no sign-up. The comparison runs entirely in your browser using JavaScript, so neither the original nor the changed text is uploaded to any server.
The primary comparison is line-based: each line of the original is matched against the revised text. Changed lines are shown as a removed/added pair so you can see the before and after.
Yes. Differences in capitalization, extra spaces, and trailing whitespace are all detected, since these often matter in code, config files, and structured data.
Yes. Any plain text works, including JSON, YAML, CSV, SQL, source code, and log files. For JSON, formatting both sides first (for example with a JSON formatter) makes structural differences easier to read.
There is no hard limit, but the underlying algorithm scales with the size of both inputs, so comparing very large files (tens of thousands of lines) may briefly slow down rendering in the browser.
A line-based diff detects presence and order, not movement. When you move a block, it appears removed from its old position and added in its new one, since the tool does not track relocated content as a single move.
Yes. Both panels remain editable, and the diff recalculates as you type, which is useful for reconciling two versions until only the intended differences remain.