JSONLint is the classic JSON validator -- paste JSON, click Validate, see if it is valid. It works. It is also a bare-bones tool that has not changed much in years, runs ads, and only validates on button click rather than in real time.
This is a comparison of JSONLint with the JSON Formatter at Ultimate Tools, which validates and formats as you type.
What JSONLint does
JSONLint validates JSON and reports the line and position of the first error. It does basic pretty-printing with indentation. The interface is minimal -- textarea in, result out. It has been useful since 2010 and still serves its core purpose.
Feature comparison
| Feature | JSONLint | Ultimate Tools JSON Formatter |
|---|---|---|
| JSON validation | Yes | Yes |
| Error location (line/col) | Yes | Yes |
| Real-time validation | No (button click) | Yes |
| Pretty-print / format | Yes | Yes |
| Minify / compact | No | Yes |
| Syntax highlighting | No | Yes |
| Tree view | No | Yes |
| Copy formatted output | Manual | One-click |
| Dark mode | No | Yes |
| Ads | Yes | No |
| Account required | No | Never |
Real-time vs button-click validation
JSONLint requires you to paste your JSON and click the "Validate" button. If you are iterating on JSON (editing, checking, editing again), this is a minor but constant friction.
The JSON Formatter validates as you type. The error message and line number update instantly with each keystroke. For debugging malformed JSON, this feedback loop is significantly faster.
Minify and tree view
JSONLint's output is always pretty-printed. If you need to minify JSON (remove whitespace for a payload, config file, or log line), you need a different tool.
The JSON Formatter has a Minify button that collapses the JSON to a single line -- useful before pasting into an API request or environment variable.
The tree view renders the JSON as a collapsible hierarchy. For deeply nested JSON (API responses, config files), being able to collapse branches makes the structure readable in a way that even well-indented JSON is not.
Common use cases
Debugging API responses -- Paste the raw JSON from a fetch response or Postman, see it formatted and validated instantly. Real-time validation catches malformed JSON (missing comma, trailing comma, unquoted keys) immediately.
Formatting before committing -- Ensure JSON config files are properly formatted before committing. Paste, format, copy back.
Minifying for environment variables -- Long JSON config strings for environment variables need to be on one line. Paste, minify, copy.
Validating webhook payloads -- Paste the webhook body from logs, validate that it is well-formed JSON before writing the handler.
Where JSONLint is still useful
JSONLint is the canonical reference for JSON validation. If you need to share a validation result with a colleague (the URL contains the JSON state), JSONLint's shareable URL is useful. The JSON Formatter does not have shareable URLs.
For a quick one-off validation where you do not need real-time feedback, JSONLint is familiar and gets the job done.
Validate and format your JSON: JSON Formatter -- real-time validation, syntax highlighting, minify, tree view. Free, no account.
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