JSON Validator
Validate JSON — pretty-print, minify, exact error messages
JSON Input
JSON Validator — Complete Guide & Instructions
MakeCard JSON Validator parses pasted JSON and tells you instantly whether it is valid — and if not, exactly why. Valid input can be pretty-printed with indentation or compressed to a single minified line, with a badge showing the root type (object, array, string and so on). It is the everyday first stop for developers debugging API payloads and config files.
How to Use JSON Validator
- 1 Paste JSON into the input box, or press “Sample” to load a working example.
- 2 Click “Validate & Format” to check syntax and pretty-print, or “Minify” to compress it.
- 3 A green badge confirms “Valid JSON” along with the detected root type.
- 4 On failure, the red badge shows the precise parser error message.
- 5 Press “Copy” to take the formatted or minified output.
Key Features & Capabilities
- Real JSON.parse-based validation with the exact engine error message.
- Pretty-print mode indents nested objects and arrays for readability.
- Minify mode strips all whitespace for compact transport or storage.
- Root-type badge — tells you whether the document is an object, array or scalar.
- Sample loader and one-click copy of the processed output.
Supported Formats & Specifications
| Parameter | Specification |
|---|---|
| Input | Any JSON text — objects, arrays, scalars |
| Modes | Validate & Format (pretty) · Minify |
| Error Reporting | Native parser message with position detail |
| Processing | Local parse in browser — instant |
Practical Everyday Use Cases
- Debugging why an API request body keeps getting rejected.
- Pretty-printing a minified config file before editing it.
- Verifying a JSON config (composer.json, tsconfig) before committing.
- Compacting JSON for query parameters or storage where size matters.
- Teaching JSON syntax — the parser message shows exactly where syntax breaks.
Pro Tips for Best Results
- The most common JSON error is a trailing comma after the last item — remove it and revalidate.
- JSON requires double quotes on keys and strings; single quotes are not valid.
- Minify before embedding JSON in URLs or environment variables to cut size dramatically.
- If the document is huge, paste a suspicious fragment — the error position often localizes the problem anyway.
Common Problems & Solutions
Look at the character position in the message — usually a missing comma, unquoted key or stray bracket near that offset.
Hidden characters from copying PDFs or chat apps (smart quotes, NBSP) break parsing — retype quotes or paste as plain text.
Validation only checks syntax, not schema — a valid document can still have wrong field names or types for your API.
Privacy & Security
100% Client-Side Execution
Parsing and formatting run locally in your browser — the JSON you paste is never transmitted or stored.
Frequently Asked Questions
Everything you need to know about using JSON Validator
Paste it into the box and click Validate & Format — a green “Valid JSON” badge confirms it, or a red badge shows the parser's error message with the failing position.
The usual culprits are trailing commas, single quotes, unquoted keys or invisible characters from copy-paste — the error message identifies the exact offset.
Paste the JSON and press Validate & Format — the output is re-indented with proper line breaks, ready to copy.
A validator only checks syntax correctness; a formatter restructures whitespace. This tool does both — it validates first, then pretty-prints or minifies on success.
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