JSONL vs NDJSON: Complete Comparison Guide

comparison-summary.txt

Quick Answer: JSONL vs NDJSON

JSONL and NDJSON are the exact same format. Both terms refer to newline-delimited JSON files where each line contains one JSON object. The only difference is the name - JSONL is more commonly used in the developer community.

JSONL vs NDJSON: The Truth

Despite the different names, JSONL and NDJSON are identical formats. Both refer to the same text-based data format where each line contains exactly one JSON object. The confusion often arises from different naming conventions used across various tools and documentation.

Key Facts

Both formats store one JSON object per line
Both use newline characters (\n) as separators
Both follow identical parsing rules
Both have the same performance characteristics
Both support the same use cases

Terminology Breakdown

JSONL (JSON Lines)

Full Name: JSON Lines
Popularity: More widely adopted
Community: Preferred by developers
Tools: Most tools use this term
Documentation: More comprehensive

NDJSON (Newline Delimited JSON)

Full Name: Newline Delimited JSON
Popularity: Less common but descriptive
Community: Used in some enterprise tools
Tools: Some tools prefer this term
Documentation: More technical/formal

Format Comparison

Let's examine the actual format structure to prove they're identical:

format-comparison.txt

JSONL Format

{"name": "John", "age": 30}
{"name": "Jane", "age": 25}
{"name": "Bob", "age": 35}

NDJSON Format

{"name": "John", "age": 30}
{"name": "Jane", "age": 25}
{"name": "Bob", "age": 35}

Identical! Both formats produce the same output.

Why Two Names for the Same Format?

The existence of two names for the same format can be attributed to several factors:

Different Origins: JSONL emerged from the developer community, while NDJSON was coined in more formal/enterprise contexts
Descriptive vs. Concise: NDJSON is more descriptive ("Newline Delimited JSON"), while JSONL is shorter and catchier
Tool Adoption: Different tools and libraries adopted different naming conventions
Documentation Standards: Various documentation standards and specifications used different terms
Community Preferences: Different developer communities preferred different terminology

Tool Support and Compatibility

Most modern tools support both terms interchangeably:

Tool/Library	Primary Term	Supports Both
jq	JSONL	✅ Yes
Python jsonlines	JSONL	✅ Yes
Node.js ndjson	NDJSON	✅ Yes
Apache Spark	JSONL	✅ Yes
Our Tools	JSONL	✅ Yes

When to Use Which Term

Use "JSONL" When:

Writing documentation for developers
Building open-source tools
Creating tutorials and guides
Working with modern data tools
Targeting the broader developer community

Use "NDJSON" When:

Writing formal specifications
Working with enterprise tools
Creating technical documentation
Need to be more descriptive
Working with legacy systems

MIME Types and File Extensions

Both formats support the same MIME types and file extensions:

Supported MIME Types

application/jsonl
application/x-ndjson
text/x-jsonl

Common File Extensions

.jsonl (most common)
.ndjson
.jsonlines

Performance and Processing

Since JSONL and NDJSON are identical formats, they have identical performance characteristics:

Aspect	JSONL	NDJSON
Parse Speed	Line-by-line	Line-by-line
Memory Usage	Low (streaming)	Low (streaming)
File Size	Same as source	Same as source
Compatibility	100%	100%

Best Practices for Both Formats

Since JSONL and NDJSON are the same format, the best practices apply to both:

Validate each line - Ensure every line contains valid JSON
Handle empty lines gracefully - Skip or ignore empty lines during processing
Use streaming for large files - Process files line by line to avoid memory issues
Maintain consistent encoding - Use UTF-8 for international character support
Implement proper error handling - Handle malformed lines without stopping processing
Consider compression - Use gzip or similar for storage and transmission

Conclusion: Choose Your Term Wisely

The choice between "JSONL" and "NDJSON" is purely a matter of preference and context. Both refer to the exact same format with identical capabilities and performance characteristics.

Our Recommendation

Use "JSONL" for most purposes as it's more widely adopted, shorter, and more recognizable in the developer community. However, don't hesitate to use "NDJSON" when working with enterprise tools or when the more descriptive name is beneficial for clarity.

[ JSONL::Tools ]