---
published: true
id: json
title: JSON
description: Knowledge captured in João Lopes' learning graph.
tags:
- format
- web
locale: en
resource: https://joaolopes.dev.br/knowledge/concepts/en/json/
created: '2026-03-28'
---

# JSON
JavaScript Object Notation, a lightweight text-based data interchange format using key-value pairs and arrays that is both human-readable and machine-parseable.

## Definition
JSON (JavaScript Object Notation) is a language-independent data format derived from JavaScript that represents data as key-value pairs and ordered arrays. It is the dominant format for data interchange on the web and in API communication. In AI agent systems, JSON serves dual roles: tool call parameters (the model produces structured JSON to specify which tool to call and with what arguments) and tool results (returned as JSON objects). Its verbosity is a tradeoff — each key-value pair costs tokens against the context window budget.

## Source
- [JSON.org](https://www.json.org/)
- [RFC 7159 — The JSON Data Interchange Format](https://datatracker.ietf.org/doc/html/rfc7159)
- [JSON — Wikipedia](https://en.wikipedia.org/wiki/JSON)

## Related
- [MCP](/concepts/en/mcp.md)
- [LLM](/concepts/en/llm.md)