Code Duplication Finder

Tool Overview

A code duplication finder compares two code snippets side by side. It shows which lines are the same, which are only in the first block, and which are only in the second. It also computes a similarity percentage so you can see how much the two blocks overlap.

Copy-pasted or similar code in different places is hard to maintain. You fix a bug in one place and forget the other. You change logic in one block and leave the other outdated. Finding and comparing duplicates by hand is slow and error-prone.

This tool takes two blocks you paste in, compares them line by line, and shows a diff with a similarity score. You can turn on ignore whitespace so spaces and blank lines do not affect the result. You can optionally ask for a refactoring suggestion that proposes one unified version and lists benefits.

The tool is for developers and anyone who edits code. You need to paste two snippets and read the diff; no extra setup is required.

Background & Concept Explanation

Duplicate code means two or more places that do the same or very similar things. Sometimes the code is copied and then changed a little. Comparing two blocks manually is tedious: you scan line by line and mentally track what matches and what does not. A related operation involves calculating code complexity as part of a similar workflow.

A line-based diff shows each line as unchanged, removed from the first block, or added in the second block. Removed lines exist only in the first snippet. Added lines exist only in the second. Unchanged lines appear in both (after normalization if you ignore whitespace).

Similarity is a number from 0 to 100. Here it is based on lines: the tool builds the set of normalized lines from each block, counts how many lines appear in both sets (intersection), and divides by the total number of unique lines in either block (union). That fraction, times 100, is the similarity percentage. So 100% means every non-empty line in one block appears in the other; 0% means no line is shared.

Ignore whitespace means before comparing, each line is trimmed and multiple spaces are collapsed to one. So two lines that differ only by spaces or indentation are treated as the same. Turning this off means the comparison is exact character-by-character per line.

Refactoring means taking two similar blocks and turning them into one reusable piece (e.g. a function) so you fix bugs and change behavior in one place. The tool can ask for an AI-generated refactoring suggestion: a summary, a single refactored code block, and a list of benefits. That suggestion is optional and does not change your pasted code; you can copy the refactored code if you want to use it. For adjacent tasks, linting code addresses a complementary step.

Key Features

• Two code blocks: you paste the first snippet in Block A and the second in Block B. Both are plain text; the tool does not run or execute the code.
• Automatic comparison: after you type or paste, the tool compares the two blocks after a short delay (debounce). You do not have to click a button to run the comparison.
• Ignore whitespace option: a toggle turns normalization on or off. When on, each line is trimmed and spaces are collapsed before comparing. When off, lines are compared exactly.
• Line-based diff: the result is a list of lines for Block A (left) and Block B (right). Each line is marked as unchanged, removed (only in A), or added (only in B). Line numbers for A and B are shown where applicable.
• Similarity percentage: a score from 0 to 100 is shown. It is based on the number of lines that appear in both blocks (after normalization if ignore whitespace is on) divided by the total number of unique lines in both blocks, times 100.
• Diff viewer: the left column shows Block A with removed lines highlighted. The right column shows Block B with added lines highlighted. Unchanged lines appear in both columns. This makes it easy to see where the two snippets differ.
• Labels for similarity: the tool labels the result as high duplication (e.g. above 80% similar), moderate similarity (e.g. 50–80%), or low similarity (e.g. below 50%). The exact thresholds may match the UI (e.g. 80 and 50).
• Refactoring analysis: an optional “Get Analysis” button sends both blocks to an AI service. The result includes a short summary, a refactored code block (one version that could replace or unify the two), and a list of benefits. You can copy the refactored code. The tool does not auto-apply it to your snippets.
• Copy refactored code: when AI analysis is shown, a copy button copies the suggested refactored code to the clipboard.
• Clear: a clear button empties both code blocks and clears the diff and any AI suggestion. Use it to start a new comparison.
• Input limits: each code block is limited in size (e.g. 500KB per block). The diff engine also limits total lines per block and the number of diff lines shown (e.g. first 2000 lines) to keep the page responsive. If you exceed size or line limits, the tool shows an error or a truncated diff message.
• Character count: each code block shows its character count so you can see how much you have pasted.

Common Use Cases

Comparing two functions: paste one function in Block A and a similar one in Block B. See the diff and similarity to decide if they are duplicates and whether to refactor into one.

Checking copy-paste edits: after copying a block and changing it, paste original and modified block in A and B. Use the diff to review every change and the similarity score to see how much stayed the same.

Before refactoring: paste two similar snippets, run the comparison, then use “Get Analysis” to get a suggested unified version and benefits. Use the summary and refactored code as a starting point; then edit in your own editor.

Code review: paste two versions of the same file or two blocks from different files. Use ignore whitespace to focus on real logic changes and the diff to see exactly what was added or removed. When working with related formats, validating code syntax can be a useful part of the process.

Learning: paste your code and a reference or solution. Compare line by line and read the similarity score to see how close your version is to the reference.

How to Use This Tool

1. Open the code duplication finder in your browser.
2. Paste the first code snippet into the box labeled “Code Block A” (placeholder: “Paste first code snippet...”).
3. Paste the second code snippet into the box labeled “Code Block B” (placeholder: “Paste second code snippet...”).
4. Optionally set “Ignore Whitespace”: turn it on to ignore spaces and blank lines when comparing; turn it off to compare lines exactly.
5. Wait a moment; the tool compares the two blocks automatically after you stop typing.
6. Below the two blocks, read the diff result: the similarity percentage and the label (e.g. high duplication, moderate similarity, low similarity).
7. Scroll through the diff viewer: left column is Block A (removed lines highlighted), right column is Block B (added lines highlighted). Use line numbers to find differences.
8. If you want a refactoring suggestion, click “Get Analysis” in the “Refactoring Analysis” section. Wait for the result.
9. When the analysis appears, read the summary and the list of benefits. To use the suggested code, click “Copy” next to “Refactored Code” and paste it into your editor.
10. To start over, click the clear (trash) button in the header. Both blocks and the diff and AI result are cleared.
11. If you see an error that code exceeds the maximum size, shorten one or both blocks (e.g. paste a smaller portion). Each block has a size limit (e.g. 500KB).

Calculations & Logic

The tool does not execute your code. It only compares two text inputs line by line.

Normalization: when “Ignore Whitespace” is on, each line is trimmed (leading and trailing spaces removed) and every run of whitespace inside the line is replaced by a single space. When it is off, lines are not changed before comparison.

Line sets: from Block A, the tool builds a set of normalized lines (empty lines are dropped). From Block B, it builds another set the same way. “Intersection” is the number of lines that appear in both sets. “Union” is the number of lines that appear in at least one set (no duplicates counted). In some workflows, beautifying source code is a relevant follow-up operation.

Similarity: similarity = (intersection / union) × 100, rounded to a whole number. If both blocks have no non-empty lines, union is 0 and similarity is set to 100. So 100% means all non-empty lines are shared; 0% means no line is shared.

Diff algorithm: the tool walks through both lists of lines in order. When the current line of A (normalized) equals the current line of B (normalized), both are emitted as unchanged. When they differ, the algorithm looks ahead a short distance to see if a later line in A matches the current line in B (then the skipped A lines are emitted as removed) or the current line in A matches a later line in B (then the skipped B lines are emitted as added). If no match is found in that window, one line from A is emitted as removed and/or one line from B as added. This produces a line-by-line diff with added/removed/unchanged. Output is capped (e.g. at 2000 lines); if the diff is longer, a truncation message is shown.

Size and line limits: each block is limited in characters (e.g. 500KB). The diff engine also limits how many lines each block can have (e.g. 10,000). If either block is over the character limit, the UI shows an error. If either is over the line limit, the diff result shows an error message instead of a full diff. The number of diff lines shown is capped (e.g. 2000) to avoid slowing the page.

Reference Tables

Tips, Limitations & Best Practices

Use “Ignore Whitespace” when you care about logic and not formatting. Turn it off when you want to see every space and indentation change. For related processing needs, finding unused CSS handles a complementary task.

Paste complete snippets (e.g. whole functions or blocks) so the diff and similarity make sense. Pasting half a function in one block and the full function in the other can make the diff harder to read.

The similarity score is based only on unique lines. Two blocks with many repeated lines (e.g. the same line 10 times) will have high similarity even if the rest of the code is different. Use the diff viewer to see the full picture.

The tool compares exactly two blocks that you paste. It does not scan a whole project or multiple files. To compare code from two files, copy each section into Block A and Block B.

AI refactoring is optional and may fail or be slow depending on the service. The refactored code is a suggestion; review and test it before using it in your project. The tool does not apply the suggestion automatically.

If the diff is truncated (e.g. “showing first 2000 lines”), the similarity score is still based on the full blocks up to the line limit. Only the displayed diff is cut off; shorten the input if you need to see the full diff.

Keep each block under the size and line limits. If you hit “Input exceeds maximum size” or “Too many lines to process”, paste a shorter portion or split the comparison into smaller chunks.

Use clear before pasting a new pair of snippets so old results do not mix with the new comparison.

The tool does not detect duplicates automatically across a codebase. You choose the two blocks to compare. For project-wide duplicate detection, use a different tool or process.