Can I set an unlimited length for maxJsonLength in web.config?

NOTE: this answer applies only to Web services, if you are returning JSON from a Controller method, make sure you read this SO answer below as well: https://stackoverflow.com/a/7207539/1246870

The MaxJsonLength property cannot be unlimited, is an integer property that defaults to 102400 (100k).

You can set the MaxJsonLength property on your web.config:

<configuration>    <system.web.extensions>       <scripting>           <webServices>               <jsonSerialization maxJsonLength="50000000"/>           </webServices>       </scripting>   </system.web.extensions></configuration> 

If you are using MVC 4, be sure to check out this answer as well.

If you are still receiving the error:

• after setting the maxJsonLength property to its maximum value in web.config
• and you know that your data's length is less than this value
• and you are not utilizing a web service method for the JavaScript serialization

your problem is is likely that:

The value of the MaxJsonLength property applies only to the internal JavaScriptSerializer instance that is used by the asynchronous communication layer to invoke Web services methods. (MSDN: ScriptingJsonSerializationSection.MaxJsonLength Property)

Basically, the "internal" JavaScriptSerializer respects the value of maxJsonLength when called from a web method; direct use of a JavaScriptSerializer (or use via an MVC action-method/Controller) does not respect the maxJsonLength property, at least not from the systemWebExtensions.scripting.webServices.jsonSerialization section of web.config. In particular, the Controller.Json() method does not respect the configuration setting!

As a workaround, you can do the following within your Controller (or anywhere really):

var serializer = new JavaScriptSerializer();// For simplicity just use Int32's max value.// You could always read the value from the config section mentioned above.serializer.MaxJsonLength = Int32.MaxValue;var resultData = new { Value = "foo", Text = "var" };var result = new ContentResult{    Content = serializer.Serialize(resultData),    ContentType = "application/json"};return result;

This answer is my interpretation of this asp.net forum answer.

In MVC 4 you can do:

protected override JsonResult Json(object data, string contentType, System.Text.Encoding contentEncoding, JsonRequestBehavior behavior){    return new JsonResult()    {        Data = data,        ContentType = contentType,        ContentEncoding = contentEncoding,        JsonRequestBehavior = behavior,        MaxJsonLength = Int32.MaxValue    };}

in your controller.

Addition:

For anyone puzzled by the parameters you need to specify, a call could look like this:

Json(    new {        field1 = true,        field2 = "value"        },    "application/json",    Encoding.UTF8,    JsonRequestBehavior.AllowGet);