The Ultimate Guide to JSON Formatting and Validation

JSON is everywhere. APIs, config files, databases, logs. Yet developers still waste hours debugging malformed JSON. Missing commas, trailing commas, single quotes instead of double quotes — these tiny errors break everything. Here's everything you need to know about JSON, from basics to advanced tooling. JSON Basics Everyone Gets Wrong Trailing Commas Are Invalid // WRONG — trailing comma after "blue" { "colors" : [ "red" , "green" , "blue" ,] } // CORRECT { "colors" : [ "red" , "green" , "blue" ] } JavaScript allows trailing commas. JSON does not. This catches everyone at least once. Only Double Quotes // WRONG — single quotes { 'name': 'John' } // CORRECT — double quotes only { "name" : "John" } No Comments // WRONG — JSON has no comments { "port" : 3000 // development port } // CORRECT — use a separate field or remove { "port" : 3000 , "_port_note" : "development port" } If you need comments, use JSONC (JSON with Comments) or JSON5. VS Code supports JSONC for settings files. Numbers