JSONEditor.io

The editor runs on Monaco, the component behind VS Code, and that choice shows up everywhere. You get syntax highlighting for JSON, YAML and XML, real-time error detection with squiggly underlines, IntelliSense and auto-completion, code folding for large files and regex find and replace. Keyboard shortcuts match VS Code, so the muscle memory carries over. The tradeoff is bundle size, but that cost stays invisible because Monaco loads in parallel with the page.

The same file can be read three ways. Text mode shows raw JSON with full editing. Tree mode renders the structure as an expandable hierarchy, which helps when a nested object has more branches than you can track by eye. Table mode lays arrays out as rows and columns, so scanning a list of records stops being a chore. You switch modes as you work, and the underlying document stays in sync.

Conversion covers JSON, YAML, CSV, XML and TypeScript, and you can move in either direction between most of them. The JSON to CSV path handles nested objects by flattening them, which is what makes the output usable in a spreadsheet. DevOps work benefits from the JSON to YAML conversion for manifests and Compose files. The TypeScript export turns a sample payload into interface definitions you can paste into a typed project.

The AI assistant lets you describe a change in plain English instead of writing a script. Ask it to extract every email address into an array or reformat a response into a different shape, and it streams the result back as it generates. The feature runs on GPT-4 through the Vercel AI SDK. This is the one part of the product that sends data off your device, and the interface says so before you use it.

Files up to 512 MB open without freezing the tab, which most browser editors cannot claim. Monaco only renders the lines you can see, so a huge document performs like a small one. Offline support means the editor keeps working after the first load, with no connection needed for formatting, validation or conversion. The combination suits developers stuck on a flight or a restricted corporate network.

The repair tool scans a broken document for the usual suspects: trailing commas, unescaped characters, missing quotes and bad escape sequences, then suggests or applies fixes. Schema validation goes the other way, checking a payload against a predefined JSON Schema so you catch structural drift before it reaches a database. Both features cover the failures that actually stop a build.

Two JSON files can be opened side by side to highlight additions, edits and deletions between versions, which turns version chasing into a quick visual check. You can also save files to the cloud and generate a shareable link, so a teammate opens the exact same document without an attachment. Multi-tab workspace keeps several files open, organized in folders, the way a code editor would.