Learn JSON

Learn JSON: Basics, Validation and the Tools

JSON is a text format with six value types and eight syntax rules, and almost every problem with it is one of those rules broken. Start with the basics, then the validation guides, then the tool comparisons when you choose what to run your JSON through.

JSON Studio Validate State of Broken JSON Glossary API33 guides

JSON basics

JSON has no comments, no trailing commas, double quotes only, and numbers that lose precision past 2^53.

What Is JSON? Plain-English Definition and ExamplesWhat is JSON? A plain-English definition with a small example, the syntax rules, common errors and fixes, and how to read, validate, format and repair it.6 min read
What Is a JSON File? Definition, Extension & How to OpenA developer's guide to JSON files: the RFC 8259 definition, the .json extension, how to open and pretty-print one, and what a JSON Schema file is.5 min read
JSON Comments: Why They Don't Exist and How to Add Them Anyway (JSONC, JSON5, Workarounds)JSON has no comment syntax — but your config files need them. This guide explains JSONC, JSON5, and four practical workarounds so you can annotate JSON without breaking parsers.11 min read
JSON Content-Type: The Correct application/json Header (and When to Use Others)The correct Content-Type for JSON is application/json. This guide explains why, covers common mistakes like text/json and text/plain, and shows how to set the header in every major language and framework.10 min read
JSON Is Lying to You: Number Precision Loss and How to Detect ItJSON silently corrupts large integers and floating point numbers. Learn why it happens, how to detect it, and how ES2026's JSON.parse source access finally fixes it.11 min read
JSON5 vs JSON: Why LLMs Produce JSON5-Flavored Output (and How to Fix It)JSON5 has 167M npm downloads per week. LLMs trained on web data produce JSON5-flavored output that silently fails JSON.parse(). Here's the difference, why it happens, and how to repair it.12 min read

Validation and schema

Validation tells you whether JSON is correct; repair makes it correct; a schema says what correct means for your data.

Tools and comparisons

Most online JSON tools format and validate; few repair, and fewer do it in the browser without uploading your data.

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Every guide here is written from reproduced cases by the maintainer of the repair engine — about the site.