Great Idea Foundry JSON Toolkit

Format, fix and convert JSON

Paste JSON and get it formatted, validated and explained as you type. Repair broken JSON, explore it as a tree, or turn it into YAML or CSV. It all runs in your browser.

JSON Toolkit is the JSON tool we wanted on our own desks: one page that formats and validates as you type, tells you exactly where an error is and how to fix it, and converts to YAML and CSV without a round trip to a server.

Errors come with the line, the column and a plain-English hint, such as a missing comma or a trailing comma before a closing bracket. Repair fixes the usual hand-written mistakes in one go: comments, trailing commas, single quotes, unquoted keys and Python True, False and None.

Numbers are kept exactly as written, so long IDs like 12345678901234567890 and prices like 1.50 are not rounded or changed. Key order is kept too, unless you ask for keys to be sorted.

Everything happens on your device. Your JSON is never uploaded, logged or stored, which makes the toolkit safe for API responses, config files and data that contains customer details.

Pick a JSON tool

Format and check

Make JSON readable, find errors and fix them.

  • JSON Formatter - Paste minified or messy JSON and get it neatly indented as you type. Choose 2 spaces, 4 spaces or tabs, sort the keys if you like, then copy or download the result.
  • JSON Validator - Paste JSON to check it against the JSON standard. Valid JSON gets a green tick and a summary; invalid JSON gets the exact line and column, the line highlighted and a hint on how to fix it.
  • JSON Minifier - Strip the spaces and line breaks out of JSON to make it as small as possible. The status bar shows how much smaller it got. The data itself stays exactly the same.
  • JSON Viewer - Turn a wall of JSON into a tree you can explore. Open and close objects and arrays, search for a key or value, and click any field to copy its JSONPath.
  • JSON Repair - Paste JSON that will not parse, from a config file, a log, a Python print or an AI answer, and get valid JSON back. Every fix is listed, so you know what changed.

Convert

Move data between JSON, YAML and CSV.

  • JSON to YAML - Paste JSON and get clean YAML as you type, ready for Kubernetes manifests, Docker Compose, CI pipelines and config files. Choose 2 or 4 space indentation.
  • YAML to JSON - Paste YAML and get formatted JSON as you type. Anchors and aliases are expanded, several documents become a JSON array, and errors show the line where the YAML went wrong.
  • JSON to CSV - Turn an array of JSON objects into a CSV file you can open in Excel or Google Sheets. Nested fields become columns like address.city, and every row gets every column.
  • CSV to JSON - Paste CSV, or copy cells straight from Excel or Google Sheets, and get a JSON array with one object per row. The separator is detected for you.

Coming soon

  • JSON Schema - Check JSON against a schema, with errors by path.
  • JSON to TypeScript - Generate types and interfaces from sample data.
  • JSONPath query - Filter and pick values with a JSONPath expression.
  • XML to JSON - Convert XML documents to JSON and back.

Frequently asked questions

Is my JSON uploaded anywhere?
No. JSON Toolkit runs entirely in your browser. Formatting, validation, repair and conversion all happen on your device and nothing is sent to our servers.
How do I find the error in my JSON?
Paste it in. If it is not valid, the toolkit highlights the line, shows the line and column, and explains the likely cause, for example a missing comma or an unquoted key. Go to error moves the cursor straight there.
What does Repair fix?
Comments, trailing commas, missing commas between items, single quotes, unquoted keys, Python True, False and None, undefined and NaN, leading zeros and several JSON values pasted one after another. It lists every fix it made.
Will large numbers lose precision?
No. The toolkit uses its own parser that keeps every number exactly as written, so long IDs and decimals like 1.50 come out unchanged. Most online formatters round them.
How are nested objects turned into CSV?
Nested objects become dotted column names, like address.city, and arrays are written as JSON text in their cell. CSV to JSON rebuilds the nesting from those dotted names.
How big a file can I open?
Several megabytes work fine. Colouring switches off above about 150 KB to keep typing smooth, and the work happens on your device, so very large files depend on your computer's memory.