isJson static method

@useResult bool isJson(String? value, { bool shouldTestDecode = false, bool shouldAllowEmpty = false, })

Returns true if value appears to be valid JSON.

If shouldTestDecode is true, actually attempts to decode to verify. If shouldAllowEmpty is true, treats '{}' and '[]' as valid JSON (defaults to false for backwards compatibility). Audited: 2026-06-12 11:26 EDT

Implementation

@useResult
static bool isJson(
  String? value, {
  bool shouldTestDecode = false,
  bool shouldAllowEmpty = false,
}) {
  if (value == null || value.length < 2) return false;

  final String trimmed = value.trim();
  final bool isObject = trimmed.startsWith('{') && trimmed.endsWith('}');
  final bool isArray = trimmed.startsWith('[') && trimmed.endsWith(']');

  if (!isObject && !isArray) return false;

  if (!_hasValidJsonContent(
    trimmed,
    isObject: isObject,
    shouldAllowEmpty: shouldAllowEmpty,
  )) {
    return false;
  }

  if (!shouldTestDecode) return true;

  try {
    return dc.jsonDecode(value) != null;
  } on FormatException catch (e, stackTrace) {
    // ignore: saropa_lints/avoid_print_error, saropa_lints/avoid_debug_print, saropa_lints/avoid_stack_trace_in_production -- intentional diagnostic logging; debugPrint is stripped in release builds
    debugPrint('JsonUtils.isJson testDecode failed: $e\n$stackTrace');

    return false;
  }
}