JSON Key Naming Conventions: camelCase vs snake_case in APIs

There is no official standard for JSON key naming. The JSON specification says keys are strings — it doesn't mandate a case convention. In practice, two conventions dominate: camelCase and snake_case.

What Major APIs Use

API / Platform	Convention	Example
Google APIs	camelCase	{"userId": 1, "displayName": "Alice"}
Twitter/X API	snake_case	{"user_id": 1, "screen_name": "alice"}
GitHub API	snake_case	{"login": "alice", "avatar_url": "..."}
Stripe API	snake_case	{"customer_id": "cus_123", "created_at": 1234}
Firebase	camelCase	{"createdAt": "...", "userId": "abc"}
AWS APIs	PascalCase	{"InstanceId": "i-123", "State": "running"}

The Case for camelCase

• Native to JavaScript — no conversion needed in frontend code
• Used by Google's JSON Style Guide
• Shorter than snake_case (no underscores)
• Natural fit for APIs consumed primarily by web/mobile clients

The Case for snake_case

• More readable — underscores create visual word boundaries
• Native to Python, Ruby, and SQL — no conversion needed in backend code
• Used by most of the largest APIs (GitHub, Twitter, Stripe)
• Consistent with database column names (which are almost always snake_case)

The Real Answer: Match Your Stack

The best convention depends on where the JSON is produced and consumed:

Scenario	Recommended	Why
JavaScript backend + JavaScript frontend	camelCase	No conversion needed anywhere
Python/Ruby backend + any frontend	snake_case	Matches backend idioms; frontends can convert
Public API consumed by many languages	snake_case	More universally readable
Internal microservices	Either (just be consistent)	Internal consistency matters most

Converting at the Boundary

In practice, many teams convert JSON keys at the API boundary. A Python backend returns snake_case, and a middleware or client-side utility converts to camelCase for the React frontend. Libraries like humps (JavaScript) and djangorestframework-camel-case (Python) automate this.

Rules for Good JSON Keys

• Be consistent. Don't mix userId and user_name in the same response.
• Use descriptive names. createdAt beats ca.
• Avoid abbreviations. organizationId not orgId.
• Use plural for arrays. items not item for a list.
• Avoid nesting deeper than 3 levels. Flatten when possible.

Convert JSON Keys Instantly

Use our JSON keys to camelCase or JSON keys to snake_case converter to transform API responses. For plain text, try the camelCase converter or the case converter hub.