What causes "Can not convert {0} to Boolean." in JamesNK/Newtonsoft.Json?

Use the nullable cast (bool?)token and coalesce: ((bool?)token) ?? defaultValue — JSON null then yields null instead of throwing.

JamesNK/Newtonsoft.Json · error · ArgumentException

Can not convert {0} to Boolean.

Error message

Can not convert {0} to Boolean.

What it means

Thrown by the explicit (non-nullable) cast operator bool(JToken) at JToken.cs:564. The operator unwraps the token to a JValue and validates its JTokenType against BooleanTypes = {Integer, Float, String, Comment, Raw, Boolean}. If the token is not a JValue at all (e.g. a JObject/JArray) or its type is outside that set (Null, Undefined, Date, Guid, Uri, TimeSpan, Bytes, Object, Array), it raises this ArgumentException.

Source

Thrown at Src/Newtonsoft.Json/Linq/JToken.cs:564

        }

        private static bool ValidateToken(JToken o, JTokenType[] validTypes, bool nullable)
        {
            return (Array.IndexOf(validTypes, o.Type) != -1) || (nullable && (o.Type == JTokenType.Null || o.Type == JTokenType.Undefined));
        }

        #region Cast from operators
        /// <summary>
        /// Performs an explicit conversion from <see cref="Newtonsoft.Json.Linq.JToken"/> to <see cref="System.Boolean"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static explicit operator bool(JToken value)
        {
            JValue? v = EnsureValue(value);
            if (v == null || !ValidateToken(v, BooleanTypes, false))
            {
                throw new ArgumentException("Can not convert {0} to Boolean.".FormatWith(CultureInfo.InvariantCulture, GetType(value)));
            }

#if HAVE_BIG_INTEGER
            if (v.Value is BigInteger integer)
            {
                return Convert.ToBoolean((int)integer);
            }
#endif

            return Convert.ToBoolean(v.Value, CultureInfo.InvariantCulture);
        }

#if HAVE_DATE_TIME_OFFSET
        /// <summary>
        /// Performs an explicit conversion from <see cref="Newtonsoft.Json.Linq.JToken"/> to <see cref="System.DateTimeOffset"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>

View on GitHub (pinned to 4f73e74372)

Solutions

Use the nullable cast (bool?)token and coalesce: ((bool?)token) ?? defaultValue — JSON null then yields null instead of throwing.
Check token.Type == JTokenType.Boolean (or is within Integer/Float/String) before the non-nullable cast.
Use token.Value<bool?>() which tolerates null/missing tokens.
Deserialize into a strongly-typed POCO with a nullable bool property instead of manual casts.

Example fix

// before
bool active = (bool)token["active"]; // throws when field is null

// after
bool active = (bool?)token["active"] ?? false;

Defensive patterns

Strategy: type-guard

Validate before calling

// Verify the token is a boolean-compatible scalar before the non-nullable cast
static bool CanToBool(JToken? t) =>
    t is JValue v && (v.Type == JTokenType.Boolean || v.Type == JTokenType.Integer
                      || v.Type == JTokenType.Float || v.Type == JTokenType.String);

Type guard

static bool? SafeBool(JToken? t) => t switch {
    JValue v when v.Type is JTokenType.Boolean or JTokenType.Integer
                       or JTokenType.Float or JTokenType.String => (bool?)t,
    JValue v when v.Type is JTokenType.Null or JTokenType.Undefined => null,
    _ => null
};

Try / catch

try
{
    bool b = (bool)token;
}
catch (ArgumentException ex) when (ex.Message.StartsWith("Can not convert"))
{
    // token type is not boolean-compatible; fall back to default
}

Prevention

Use the nullable cast (bool?)token for optional/nullable boolean fields.
Check token.Type before applying the non-nullable bool cast.
Prefer token.Value<bool?>() which tolerates missing/null tokens.
Deserialize into a nullable bool POCO property for schema-driven safety.

When it happens

Trigger: Casting a JSON null (JTokenType.Null) to (bool)token; casting a JObject/JArray/JConstructor to bool; casting a Date/Guid/Uri/TimeSpan JValue to bool; calling (bool)token where token.Type is Object or Array.

Common situations: A JSON schema change that made a previously-boolean field null or an object; consuming an API that omits the field (parsed as null); treating a nested object/array as a scalar boolean.

Related errors

AI-assisted analysis of JamesNK/Newtonsoft.Json@4f73e74372 (2026-08-07). Data as JSON: /api/errors/48c23436b59595d1. Report an issue: GitHub.