JSON Canonicalizer

What is JSON Canonicalization?

RFC 8785 (JSON Canonicalization Scheme, JCS) defines a deterministic serialization format for JSON. It enables consistent hashing and signing of JSON payloads regardless of how the original JSON was formatted.

// Input (any order, any whitespace)
{
  "zebra": "last",
  "apple": "first"
}

// Canonical form (RFC 8785)
{"apple":"first","zebra":"last"}

Using Canonical JSON for Signing

// Node.js example
const crypto = require('crypto');

function canonicalize(val) {
    if (val === null || typeof val !== 'object') return JSON.stringify(val);
    if (Array.isArray(val)) return '[' + val.map(canonicalize).join(',') + ']';
    const sorted = Object.keys(val).sort();
    return '{' + sorted.map(k => JSON.stringify(k) + ':' + canonicalize(val[k])).join(',') + '}';
}

const canonical = canonicalize({ b: 2, a: 1 });
// -> {"a":1,"b":2}

const hash = crypto.createHash('sha256').update(canonical).digest('hex');

Common Use Cases

• JWS / JWT Signing: Canonicalize payload before computing HMAC or RSA signature
• Webhook Verification: Hash the canonical body to verify HMAC signatures from providers
• Content Addressing: Compute stable content hashes for JSON documents in IPFS / CAS systems
• Blockchain / Smart Contracts: Deterministic JSON encoding before on-chain storage or hashing
• API Response Caching: Cache-key generation based on normalized request parameters
• Data Deduplication: Identify duplicate JSON payloads with different key orderings

FAQ