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JSON Formatter & Validator
How do I format and validate JSON?
Format, minify, and validate JSON data.
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JSON: The Language of Data
Key Insights & Concepts
JSON (JavaScript Object Notation) is the lingua franca of the API world. Since displacing XML in the early 2000s, it has become the universal standard for data interchange. But writing it manually is prone to distinct, frustrating errors.
The "Strict" Standard
JavaScript objects allow trailing commas, single quotes, and keys without quotes. JSON does not.
- ❌ { key: "value" } // Missing quotes
- ❌ { "key": 'value' } // Single quotes
- ❌ { "key": "value", } // Trailing comma
The Valid Format
To parse safely across all languages (Python, Go, Java), JSON must be perfect.
- ✅ { "key": "value" }
- ✅ [1, 2, "three"]
- ✅ { "nested": null }
Deep Dive: The BigInt Limit
This is the #1 bug in financial and social media applications.
{ "id": 9223372036854775807 }
// What JavaScript sees after JSON.parse()
{ "id": 9223372036854776000 }
Why? JavaScript uses IEEE 754 floating-point numbers. It cannot precisely represent integers larger than 2^53 - 1.
The Fix: Always instruct your backend team to return large 64-bit IDs as Strings (`"id": "123..."`), not numbers.
Security: Prototype Pollution
Never blindly trust JSON from an API. If an attacker sends a key named `__proto__`, unsafely merging that JSON into your state could corrupt every object in your application.
1. Use `Map` instead of Plain Objects where possible.
2. Freeze the Object prototype: `Object.freeze(Object.prototype)`.
3. Most importantly: Validate structure with a library like Zod before usage.