Code Diff Checker
Compare two code snippets line by line without uploading them. Your work stays on this device whenever possible.
How to use Code Diff Checker
- Paste the older version into "Original Code" and the newer one into "Modified Code"; a pair of small add() functions is preloaded.
- Pick "Unified Diff (.patch)" or "Line-by-Line Changes & Statistics" in "Diff View Format".
- Tick "Ignore whitespace" to collapse runs of spaces and trim each line before comparing, and "Ignore case" to fold letters together.
- Press "Compare Code" and read the patch text: a leading minus marks a removed line, a plus an added line, and two spaces a line kept.
- In the statistics view, check Lines Added, Lines Removed, Unchanged Lines and the Difference Status sentence above the patch.
Worked example
Compare the preloaded pair. The original has 4 lines and the modified version 5. Because lines are matched by position, the statistics view reports Original Lines 4, Modified Lines 5, Lines Added 5, Lines Removed 4 and Unchanged Lines 0, even though the closing brace survives in both versions at a shifted position. The status line says Differences detected.
When to use this tool
- Confirming that a line-for-line edit to a config file changed only what you intended.
- Using "Ignore whitespace" to prove a reformatting pass did not touch any code.
- Comparing two short snippets from a code review without opening an editor.
Important limitations
Runs entirely in browser memory. Extremely large source repositories exceeding 100,000 lines should be split into individual module files to maintain smooth UI rendering performance.
Frequently asked questions
How does it pair up lines?
Strictly by position: line 1 with line 1, line 2 with line 2, and so on. It does not look for moved or shifted lines, so inserting one line near the top marks everything below it as changed. For text where lines shift, the Text Diff tool on this site aligns them properly.
Is the output a valid patch file?
It looks like one, but the header is a single "@@ -1,N +1,M @@" hunk covering the entire file, with the labels original and modified. Tools that apply patches may reject it, so use it for reading rather than applying.
What exactly do the statistics count?
A pair of differing lines counts once as removed and once as added, and leftover lines at the end count as pure additions or removals. The totals can therefore exceed the number of lines you truly edited whenever content shifts.
Do the ignore options alter the printed lines?
No. They only affect the comparison. Lines are printed exactly as typed, and when two lines match after normalising, the original left-hand line is shown as unchanged.
Does it understand programming languages?
There is no syntax awareness, colouring or word-level marking, so any text works, but a one-character edit flags the whole line. That also means comments, strings and prose are treated identically.