FormatKit: Free developer toolkit — 65 browser tools for JSON, XML, YAML, CSV, SQL, Markdown and base64, with no signup and no daily quota. Format, validate, convert, compare, encode and minify payloads up to 5 MB without leaving the tab. Each tool is a JavaScript program that runs on your own machine, so JavaScript has to be enabled for the tools themselves to work. Everything written around them — instructions, specifications and answers — is plain HTML and readable without it.

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Practical guides on JSON, data formats and developer tooling.

August 10, 2026

Common JSON Syntax Errors and How to Fix Them

Trailing commas, single quotes, unquoted keys, comments — a field guide to the JSON mistakes that break parsers, with the fix for each one.