JSON Diff & Compare

What is JSON Diff?

// Two JSON documents that look different but are semantically equal
const a = '{"a":1,"b":2}';
const b = '{"b":2,"a":1}';

// Naive comparison — wrong
JSON.stringify(JSON.parse(a)) === JSON.stringify(JSON.parse(b));
// → false (key order differs)

// JSON Diff (this tool) — correct: key order is irrelevant
// → 0 differences

// JSON Patch (RFC 6902) for { "a": 1 } → { "a": 2 }
// [{ "op": "replace", "path": "/a", "value": 2 }]

Key Features

Examples

{"user":{"id":1,"name":"Ada","createdAt":"2024-01-01"}}

{"user":{"id":1,"name":"Ada Lovelace","createdAt":"2024-02-02"}}

{"a":1,"b":2,"c":3}

{"c":3,"a":1,"b":2}

[{"id":1,"qty":3},{"id":2,"qty":5}]

[{"id":2,"qty":5},{"id":1,"qty":4}]

{"items":[{"id":1,"price":29.99}]}

{"items":[{"id":1,"price":24.99}]}

How to Use

1. 1

   Paste both JSON documents

   Paste the original (left) and modified (right) JSON. Live diff renders as you type; large inputs (>200 KB) switch to a manual Diff button.

2. 2

   Filter the noise

   Click a preset (Timestamps / IDs / Trace) or paste Extended JSON Pointer patterns into Ignore paths to drop irrelevant fields.

3. 3

   Pick the view you need

   Side-by-Side for human review, JSON Patch (RFC 6902) for machine-applicable ops. Use Share Link to send the configuration to a teammate.

Common Diff Pitfalls

diff a.json b.json   # text diff: 'everything changed'

JSON Diff (this tool): 0 differences

{"a": null} == {}   # collapsed by some tools

{"a": null} ≠ {}     # type-strict diff

Sequential diff: 4 modified

Match by key (id): 0 differences

{"id": 42} vs {"id": "42"}   # serialization bug

Diff reports 'modified (type)' with both values

tolerance=0:  0.30000000000000004 ≠ 0.3

tolerance=1e-9: equal

Diff: 47 modifications (45 are timestamps)

Add /createdAt, /updatedAt, /requestId to Ignore paths → 2 real changes

Common Use Cases

API Response Regression

Compare staging vs production responses; ignore timestamps and request IDs to surface only meaningful payload changes.

CI Snapshot Test Failures

Paste actual vs expected from a failing Jest/Vitest snapshot. Filter noise and find the real change in seconds.

package-lock / yarn.lock Conflicts

Resolve merge conflicts by aligning dependencies on name; key order and unrelated fields stop being noise.

K8s / Helm Values Audit

Match envs, volumeMounts, and ports by name. Catch unintended ordering vs real config edits.

i18n Translation Coverage

Diff en.json against zh.json structurally to find missing or extra translation keys without value-noise.

Terraform / CDK Plan Review

Compare plan output across runs; numeric tolerance handles floating-point arithmetic, ignore paths drop ARNs and timestamps.

Technical Details

RFC 6902 Compliant Patch Output

Generates valid JSON Patch ops (add/remove/replace) with RFC 6901 paths. Verified against fast-json-patch@3.x and rfc6902 npm packages.

Iterative Traversal

Explicit-stack traversal (no recursion) caps at 100,000 nodes and depth 64 to prevent stack overflow on adversarial inputs.

Object.is Numeric Equality

Default numeric tolerance is 0 — uses Object.is so -0 and +0 are distinguished. Set tolerance > 0 for epsilon-based equality.

Best Practices

Filter Before Reviewing

Add Ignore paths first (timestamps, IDs, trace fields), then read the diff. Reviewing noisy diffs trains the eye to skip — and miss — real changes.

Match-by-Key for Logical Sets

If your array represents an unordered set (envs, users, dependencies), Match by key. Sequential diff on logical sets is almost always wrong.

Share Link, Not Inputs

Use Share Link to send a colleague your filter configuration — never paste sensitive JSON into shared docs. The URL contains only the config.

Frequently Asked Questions