LocalDevTools 100% Free & Client-Side

Code & Text Diff Checker Studio

/compare/ MYERS ALGORITHM · 100% PRIVATE

Side-by-Side Dual Panels · Unified Stream · Curtain Slider · Intra-Line Precision · .patch Export · 100% Client-Side

Diff:
Diff 1 of 4
Metrics:+12 Additions-0 Deletions~9 Modified=5 Unchanged
25% Match
Mobile Panel:
Original (Deletions & Replaced)
14 lines
1
-
function calculateOrderTotal(items, discountCode) {
2
let subtotal = 0;
3
-
for (let i = 0; i < items.length; i++) {
4
-
subtotal += items[i].price;
5
}
6
7
-
if (discountCode === "SAVE10") {
8
-
subtotal = subtotal * 0.9;
9
-
} else if (discountCode === "VIP20") {
10
-
subtotal = subtotal * 0.8;
11
-
}
12
13
-
return subtotal;
14
}
Modified (Additions & Updates)
26 lines
1
+
interface CartItem {
2
+
id: string;
3
+
price: number;
4
+
quantity?: number;
5
+
}
6
+
7
+
function calculateOrderTotal(items: CartItem[], discountCode?: string): number {
8
+
if (!items || items.length === 0) return 0;
9
+
10
let subtotal = 0;
11
+
for (const item of items) {
12
+
subtotal += item.price * (item.quantity ?? 1);
13
}
14
15
+
const discountRates: Record<string, number> = {
16
+
SAVE10: 0.10,
17
+
SAVE20: 0.20,
18
+
VIP20: 0.20,
19
+
FREESHIP: 0.05,
20
+
};
21
22
+
const discount = discountCode ? (discountRates[discountCode] ?? 0) : 0;
23
+
const finalTotal = subtotal * (1 - discount);
24
+
25
+
return Number(finalTotal.toFixed(2));
26
}
Workstation Mode:Side-by-Side Dual Synchronized·4 change hunks detected
100% Client-Side Myers Algorithm

Understanding File Diffing, Myers' Algorithm, and Intra-Line Precision

In software engineering, content revision, and data auditing, computing differences between two versions of a document is a fundamental operation. Whether you are conducting a code review before merging a pull request, inspecting configuration drifts across staging and production clusters, or reviewing legal contract amendments, identifying what changed, where it changed, and what remained untouched requires mathematically sound comparison algorithms.

At the mathematical core of modern version control systems like Git lies Eugene Myers' O(ND) Difference Algorithm. Originally published in 1986, Myers' algorithm frames the comparison problem as finding the shortest edit path across an edit graph from an initial string $(A)$ to a modified string $(B)$. Horizontal steps represent character or line insertions, vertical steps represent deletions, and diagonal steps represent matching (unchanged) tokens. By minimizing the edit distance while prioritizing contiguous runs of matches, Myers' algorithm computes the cleanest, most human-readable diff possible.

The LocalDevTools Code & Text Diff Checker Studio pairs Myers' line-level difference calculation with intra-line token precision. Traditional line-based diff tools mark an entire 200-character line as changed even if only a single variable name or typo was edited, forcing the reviewer to scan the line manually. Our studio calculates secondary word-level or character-level diffs within modified lines, highlighting the exact inserted or deleted tokens with vivid, high-contrast badges. Furthermore, all calculations execute 100% client-side in your browser's WebAssembly and JavaScript V8 engine—your confidential intellectual property, proprietary source code, or legal agreements are never transmitted to any third-party server or cloud database.

How to Compare Files, Inspect Differences, and Export Patches

  1. Input Your Content: Switch to the Edit Inputs view to paste your original text on the left and modified version on the right. Alternatively, click Up Left or Up Right to upload source code files directly from your computer, or choose from our curated presets (TypeScript, JSON, Python, SQL, CSS, or Prose).
  2. Select Your Inspection Mode: Toggle between Side-by-Side (dual synchronized panels with connected line numbers), Unified Stream (standard inline patch view with + and - indicators), or the signature Curtain Slider (interactive draggable split-screen divider).
  3. Fine-Tune Diff Sensitivity: Adjust whitespace handling (strict comparison, ignore leading/trailing trim, or collapse all whitespace), toggle case sensitivity (Aa), or switch intra-line precision between Words and Characters to isolate subtle punctuation or typo edits.
  4. Navigate Changes with Hunk Jumpers: Use the [▲ Prev] and [▼ Next] buttons on the master toolbar to jump directly to each modified block across thousands of lines of code.
  5. Export or Copy: Click Export .patch to download a standard unified diff file ready for Git application, or copy the formatted diff summary or unified patch directly to your clipboard.

Frequently Asked Questions (FAQ)

What is the difference between Side-by-Side (Split) diff and Unified diff? ↓

Side-by-Side (Split View) presents the original file on the left and the modified file on the right in two vertically synchronized viewports. Lines that were deleted appear in red on the left with empty spacer rows on the right, while additions appear in green on the right with spacer rows on the left. This preserves horizontal context and is ideal for comparing broad layout or architectural refactors. Unified Diff consolidates all changes into a single chronological stream using - prefixes for deleted lines and + prefixes for added lines, matching the output of git diff and Unix diff -u.

How does intra-line character and word precision highlighting work? ↓

When a line is modified rather than completely replaced, standard diff tools highlight the whole line, leaving you to guess what changed. LocalDevTools performs a secondary diff pass on paired lines using character-by-character or word-boundary tokenization. The unchanged portions of the line retain neutral background styling, while the specific inserted or deleted tokens receive bright, high-contrast badges (e.g. rose-300 for removed tokens, emerald-300 for added tokens), allowing you to pinpoint changes in fractions of a second.

How do I apply an exported .patch file to a Git repository? ↓

The Export .patch feature creates a standard POSIX unified diff file. You can apply it to your local files using either Git or standard Unix patch tools:

git apply localdevtools-diff.patch
or using the Unix patch command:
patch target_file.txt < localdevtools-diff.patch

Is my confidential code or legal document safe from server logging? ↓

Yes, 100%. Many online diff utilities upload your text to cloud servers to execute backend diff scripts, creating massive security and compliance risks for enterprise codebases, trade secrets, and proprietary contracts. LocalDevTools executes all diffing, tokenization, and patch generation completely inside your local browser memory using JavaScript and Web APIs. No network requests are made, no telemetry logs your data, and your files never leave your device.

What is the Curtain Slider and when should I use it? ↓

The Curtain Slider is LocalDevTools's signature interactive split-screen divider. It overlays the original version directly on top of the modified version using hardware-accelerated CSS polygon clipping. Dragging the divider left or right reveals before and after states in the exact same physical coordinates on your screen. This is particularly valuable for inspecting whitespace shifts, code indentation alignment, SQL query clause rewrites, and typography adjustments where side-by-side eyeshifting would make subtle layout changes hard to spot.