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Text Diff Checker

In-browser only Myers diff FileReader API
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Text Diff Checker
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Overview

About the Text Diff Checker

Compare two blocks of text and see every difference highlighted by line and by character. All processing happens in your browser — your text stays private.

  • Line-by-line Myers diff algorithm
  • Character-level highlighting within changed lines
  • Side-by-side and unified diff views
  • Ignore whitespace and case options
  • File drag-and-drop support
  • Navigate changes with arrow keys or keyboard shortcuts
  • All comparison happens locally in your browser
  • Your text is never sent to any server
  • Works offline after the page loads
  • Text disappears when you close or refresh the page
  • Review edits in a document or email draft
  • Compare two versions of a configuration file
  • Spot changes between code revisions before committing
  • Check contract or proposal revisions side by side
  • Verify data migration output against the source

Getting started

How to compare two texts

  1. 1
    Paste your original text

    Type or paste the first version of your text into the Original box on the left. You can also drag and drop a text file directly onto the box.

  2. 2
    Paste your modified text

    Add the second version to the Modified box on the right. The diff computes automatically as you type — no button needed.

  3. 3
    Read the colour-coded result

    Green lines were added, red lines were removed, and yellow lines were changed. Within yellow lines, the specific changed characters are highlighted in a stronger tint.

  4. 4
    Reduce noise with options

    Use Ignore case or Ignore whitespace to filter out formatting-only differences. Toggle Hide unchanged to collapse identical lines and focus on what changed.

  5. 5
    Navigate and copy

    Use the arrow buttons or press n and p to jump between changes. Click Copy diff to copy the full result as plain text.

Reference

What the markers mean

What the markers mean
MarkerMeaning
+ (green)Line was added in the Modified version.
− (red)Line was deleted from the Original version.
~ (yellow)Line was modified — both versions are shown with character-level highlights.
(plain)Line is identical in both versions.

Watch out for

Common diff pitfalls

Frequently Asked Questions

Does my text get sent to a server?
No. Everything happens in your browser — the diff computation, the file reading, the display. Your text never leaves your device.
What is the Myers diff algorithm?
The Myers diff algorithm (Eugene W. Myers, 1986) finds the shortest edit script between two sequences — the minimal set of insertions and deletions that turns one text into the other. It is the same algorithm used by git diff and GNU diff.
What is the difference between Side-by-Side and Unified views?
Side-by-Side shows Original on the left and Modified on the right, with matching lines aligned. Unified shows both in a single column with + and − prefixes — the same format git diff outputs in a terminal.
Is there a size limit?
The tool accepts up to 500,000 combined characters across both inputs. Most everyday comparisons are well within this limit. A non-blocking note appears above 400,000 characters.
Can I compare code files?
Yes. Drag and drop code files (.js, .ts, .py, .json, .yaml, and others) onto either input box. The file loads instantly via the FileReader API — nothing is uploaded.
Why do identical inputs show as modified?
Check your whitespace mode and case settings. A trailing space, a different line ending, or a case difference can mark a line as changed. Use the Ignore options to filter these out.