Free Online JSON Diff Tool

Instantly Compare JSON Visually

A semantic JSON diff tool that understands structure — not just text. Detect value changes, type mismatches, and missing properties with full key-path context.

Base JSON

Contrast JSON

Features

A client-side JSON comparison tool that parses structure semantically — not just text. Fast, private, and free for developers.

Semantic Diff Visualization

Color-coded highlights for every difference: green for additions, red for deletions, yellow for value changes. Full key-path reporting for nested objects.

Instant Comparison

Efficient recursive algorithms compare JSON objects with thousands of keys in under a second. No server round-trip, no loading spinners.

100% Client-Side & Private

All JSON parsing and diffing happens in your browser using JavaScript. Your data never leaves your device — zero server uploads, zero logging.

How to Compare JSON

Start comparing JSON data in three simple steps — no installation or signup needed.

01

Enter Your JSON

Enter or paste two JSON objects into the left (Base) and right (Contrast) editor panels. You can also drag-and-drop files or import from a URL.

02

Run the Comparison

Click the 'Compare' button. The tool instantly parses both inputs, normalizes structure, and produces a semantic diff.

03

Review the Diff Results

View color-coded diff results with additions, deletions, and modifications highlighted inline. Navigate differences by category in the sidebar.

How Semantic JSON Comparison Works

Unlike text-based diff tools, our JSON comparator understands data structure. It parses, normalizes, and recursively compares — so formatting changes and key reordering never produce false diffs.

01

Parse & Normalize JSON

Both JSON inputs are parsed into tree structures. Object keys are sorted alphabetically, and whitespace is normalized — so reformatting never creates false positives.

02

Recursive Deep Diff

The algorithm traverses both JSON trees recursively, comparing values at each key path. It detects type changes, value changes, additions, and deletions at every nesting level.

03

Smart Array Comparison

Arrays support three comparison strategies: By Index (positional matching), LCS (Longest Common Subsequence for intelligent insertion/deletion detection), and Unordered (set-like comparison ignoring element order).

04

Visual Diff Rendering

Each difference is mapped to its source position and rendered with color-coded highlights — green for additions, red for deletions, yellow for modifications — with full JSON path context.

Use Cases

JSON comparison is essential across many development workflows.

API Response Testing

Compare expected vs actual API responses to catch regressions. Verify endpoint behavior during development, QA, and automated CI/CD pipelines.

Configuration File Diff

Track changes between configuration file versions — package.json, tsconfig.json, Kubernetes manifests, or any structured config in JSON format.

Data Transformation Validation

Verify ETL pipeline outputs by comparing source and transformed JSON objects. Ensure data integrity across processing stages.

State Debugging & Inspection

Capture application state as JSON at different points in time and diff them to quickly identify unexpected mutations and side effects.

Load JSON Data via URL

Load JSON data into the comparison result page by passing URL query parameters. Useful for sharing diff results, CI/CD integration, or linking from documentation.

Load JSON from File URL

Pass publicly accessible URLs to the base and contrast parameters. The tool will fetch and compare the JSON content from these URLs automatically.

Load JSON from Base64

Encode your JSON content as a Base64 string and pass it directly in the URL. Use base-64.com to encode/decode your data.

FAQ

01Is my JSON data sent to a server?
No. All JSON parsing and comparison happens entirely in your browser using JavaScript. Your data never leaves your device — we don't collect, transmit, or store any of the JSON you input. The tool works even offline once loaded.
02How large of a JSON file can this tool handle?
The tool uses efficient recursive algorithms with optimized memory usage. It handles JSON files with tens of thousands of keys and deeply nested structures, typically completing comparisons in under a second.
03What array comparison modes are available?
Three modes: 'By Index' compares elements at the same array position, 'LCS' (Longest Common Subsequence) intelligently detects insertions and deletions while preserving order, and 'Unordered' treats arrays as sets — ignoring element order entirely.
04Does it detect type changes (e.g. number vs string)?
Yes. The comparator is type-aware — it distinguishes between 42 (number) and "42" (string), true (boolean) and "true" (string), null and "null". Type mismatches are reported separately from value changes.