JSON validator online

Processed locally

app.validator.view

You can also load data via #data={"name":"Ada"} or #url=... It is cleared from the address bar after it is read.

Checks whether JSON can be parsed. During API integration, confirm the payload is valid before Diff or conversion—it saves a lot of detours. On failure it tries to point to a location so you can match the Network panel or the original log.

Validate only

Success confirms it is parseable. Failure points out common syntax issues. It does not rewrite your text or silently “fix” trailing commas.

Useful for a manual check before CI, or to scan a snippet from a colleague before using it further.

Runs locally

Payloads never leave the browser, which fits response bodies that contain user data. Refresh the page and the input is cleared.

Unlike “paste JSON onto a third-party site,” all computation stays on this device.

Relation to format

The formatter also validates. This page is for “I only want to know whether this string is valid.” You do not pick indent or sort first.

After it passes, format, Diff, or convert to YAML with a clearer flow.

Example

Input that may fail

{
  "status": "ok",
  "data": {
    "items": [1, 2, 3,]
  }
}

Note

 Standard JSON does not allow a trailing comma in arrays or objects. Remove the comma after 3 to pass. If you must keep trailing commas, use the JSON5 tool.

Why do trailing commas fail?

RFC 8259 does not allow them. When config files often have trailing commas, use JSON5 to convert to standard JSON first.

Does a passing check mean the business data is correct?

It only guarantees valid syntax, not that fields match your API docs. Use Schema for structural constraints.

Are single quotes allowed?

Standard JSON allows double quotes only. Content copied from a JavaScript object should go through JSON5 first, or quotes should be fixed by hand.

What if the error line number looks wrong?

Make sure you did not paste several log fragments together. Keep only the complete document starting at the first { or [ and try again.

Recommended workflow

Paste an API response, a config snippet, or JSON from a colleague.
See whether the result is valid or an error with line and column.
Fix syntax issues, then format, Diff, or generate code.
If you need to enforce structure (required fields, types), take a sample to the Schema page for a draft.

A passing check only means “it can parse,” not that every field is present. Before a release, still compare against API docs or JSON Schema.