All JSON guides
Newest first. Each one names the runtime its outputs came from.
Duplicate JSON Keys: .NET Gives Three Different Answers to One String
Node, Python and Go take the last value; .NET's three JSON APIs return the last value, both values, and a thrown exception.
JSON Schema Validation: Undeclared Properties Pass by Default
Undeclared properties pass by default; 30.0 is an integer and true is not. All measured.
JSON in Python: The Four Defaults That Surprise People
ensure_ascii, NaN accepted by default, key coercion, and the True/1 collapse. All measured.
JSON Escape Characters: What Must Be Escaped, and What Must Not
Seven characters plus everything below U+0020 must be escaped; the slash and non-ASCII must not.
JSON vs JSON5 vs JSONC: What Strict JSON Actually Rejects
The eight things strict JSON rejects, what each extension adds, and why they belong in files rather than on the wire.
JSON Big Numbers: Why JSON.parse Silently Corrupts Large IDs
Why JSON.parse silently rounds integers past 2^53-1, why a reviver cannot fix it, and what to send instead.