Structural JSON Diffing & Semantic Comparison Algorithms

Standard line-by-line diff tools (like Git diff) often fail on JSON because unordered keys and formatting variations produce false positives. Structural JSON diffing analyzes the hierarchical tree.

1. Semantic vs Lexical Diffing

• Lexical Diff: Compares text line-by-line. Sensitive to spaces, indentation, and key reordering.
• Structural / Semantic Diff: Parses both inputs into abstract syntax trees, normalizes key orders, and compares value types and leaves.

2. The Myers Diff & Tree Delta Model

The diff engine classifies changes into 4 atomic states:

• ADDED: A key or array index present in the Right payload but absent in Left.
• REMOVED: A key or array index present in Left but absent in Right.
• MODIFIED: The key exists in both, but primitive values or types differ.
• UNCHANGED: Identical key and value.

// Delta node representation
type Delta = {
  path: string;
  type: 'added' | 'removed' | 'modified' | 'unchanged';
  leftValue?: any;
  rightValue?: any;
};