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Text Diff Checker

Compare two text blocks, source code files, or configuration documents side-by-side. Highlight line-by-line and character-level insertions, deletions, and word modifications client-side with complete privacy.

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Learn About This Tool

Understanding Diff Algorithms & Longest Common Subsequence (LCS)

Text difference (diff) tools compare two versions of a document to highlight what was added, deleted, or modified. Under the hood, this tool utilizes a character and line-level Longest Common Subsequence (LCS) algorithm similar to Git diff engines. It identifies matching line structures and computes minimal edit paths to highlight changes cleanly.
// Git-Style Unified Diff Output:
@@ -1,3 +1,3 @@
  function calculateTotal(price, tax) {
-   return price + tax;
+   return price * (1 + tax);
  }
  • Split View: Aligns original and modified documents side-by-side in parallel columns
  • Unified View: Stacks insertions and deletions sequentially in a single column
  • Character Highlights: Shades exact word and letter changes inside modified lines
  • Calculates additions (green), deletions (red), and unchanged line context

Split View vs Unified View Comparison Modes

Selecting the optimal diff layout depends on your workflow. Split View is ideal for side-by-side code reviews and comparing database configuration files. Unified View provides a compact, git-style patch layout ideal for reviewing documentation edits or commit diffs.
  • Split View: Parallel line alignment with filler padding rows for easy visual comparison
  • Unified View: Compact single-column view matching standard Git terminal diffs
  • Ignore Whitespace: Suppresses spacing, tab, and indentation differences
  • Ignore Case: Normalizes letter casing differences (e.g. `USER` vs `user`)

Character-Level Word Diff Highlights

Standard diff tools only check line additions and removals. When a single word or punctuation mark is modified in a 200-character line, finding the exact change manually is frustrating. Our engine performs a second-pass character LCS comparison on modified lines to highlight the exact modified characters. For auto-formatting code before diffing, use our JSON Formatter.
  • Shades deleted characters in darker red inline highlights
  • Shades inserted characters in darker green inline highlights
  • Identifies misplaced commas, typos, and syntax adjustments instantly
  • Handles multiline code scripts and raw prose text documents

Privacy-Preserved Local Diff Verification for Secret Code & Configs

Many web-based diff utilities upload your text strings to remote backend servers to compute diffs. This utility executes 100% locally in your browser memory. Your proprietary source code, database connection strings, API keys, and sensitive documents never leave your machine. For entity-encoded documents, try our HTML Entity Converter.
  • Zero server logging or HTTP network requests during comparison
  • Safe for API tokens, secret keys, environment variables, and legal text
  • Handles large documents up to 50,000 lines without latency
  • No account creation or subscription required

How to Use Text Diff Checker

1

Input Original & Modified Text

Paste your baseline text into the left (Original) panel and your updated text into the right (Modified) panel.

2

Adjust Comparison Settings

Toggle between Split and Unified view modes, and enable 'Ignore Whitespace' or 'Ignore Case' if formatting differs.

3

Inspect & Review Diff Results

Examine the highlighted output panel. Red blocks show deleted lines/characters, while green blocks show additions.

Code Implementations

Copy & paste production-ready code snippets for Text Diff Checker in your language of choice

File: text_diff.py
Python
import difflib

text1 = "apple\nbanana\ncherry".splitlines(keepends=True)
text2 = "apple\nblueberry\ncherry".splitlines(keepends=True)

diff = difflib.unified_diff(text1, text2, fromfile='old.txt', tofile='new.txt')
print(''.join(diff))

Frequently Asked Questions

LCS (Longest Common Subsequence) is a computer science algorithm that identifies the longest sequence of lines or characters shared between two documents to calculate minimal insertion and deletion steps.
Yes. The diff comparison runs 100% locally inside your browser using client-side JavaScript. No text is transmitted to any external server.
When enabled, trailing spaces, tabs, and indentation changes are ignored during comparison, highlighting only actual text content changes.
Yes! You can paste source code files, JSON configurations, HTML templates, CSS rules, or plain text articles.
The left column lists original line numbers, and the right column lists modified line numbers. Empty rows are aligned to keep matching lines side-by-side.
When a line is modified, the engine calculates character-level diffs within that line range to highlight the exact characters or words changed.
Yes. The in-memory JavaScript diff engine handles documents up to 50,000 lines efficiently.
Filler rows (where lines exist in one file but not the other) render with light gray backgrounds to maintain visual alignment across columns.
When 'Ignore Case' is active, uppercase and lowercase letters (e.g. `DATA` and `data`) are treated as identical during comparison.
Yes. For best results, format both JSON files first using our JSON Formatter so keys and values align cleanly line-by-line.
Yes. You can paste raw HTML strings to compare template changes, class attributes, or text content updates.
The Unified View output displays standard `+` and `-` markers matching git diff patch formats, which you can copy into your notes.
Yes. The diff checker interface scales down responsively for mobile and tablet screens.
Press `Ctrl+L` (or `Cmd+L` on Mac) to clear both text editors instantly.

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