JSON
JavaScript Object Notation: a lightweight text format for data interchange using key-value pairs and arrays. The lingua franca of web APIs.
What is JSON?
JavaScript Object Notation: a lightweight text format for data interchange using key-value pairs and arrays. The lingua franca of web APIs.
JSON is a foundational concept that sits in the Core Fundamentals area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "JSON" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
Learn JSON in depth
Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
Open the JSON lessonRelated lessons
Lessons that touch on JSON as part of a larger topic.
Document Stores
Databases that think in JSON, flexible schemas for modern applications
intermediate · database types storage
Structured Logging
Logs as data, not text, making every log line queryable and machine-parseable
intermediate · observability monitoring
JSON Schema
Data structure validation format for JSON documents
foundation · core fundamentals
MessagePack
JSON but binary, a compact serialization format that is schema-less and fast
intermediate · api design protocols
Schema Validation
Define the expected shape of your data with schemas, and reject anything that does not conform
intermediate · data governance compliance
See also
Related glossary terms you might want to look up next.
REST API
An architectural style for building APIs using standard HTTP methods (GET, POST, PUT, DELETE). Resources are identified by URLs.
XML
Extensible Markup Language: a verbose, tag-based format for structured data. Still used in enterprise systems, SOAP, and configuration files.
HTTP
The protocol powering the web. A request-response model where clients ask for resources and servers respond. Stateless by design.