How do you debug your Nest queries?

You can get the values of search request URL and JSON request body as under:

var requestURL = response.RequestInformation.RequestUrl;
var jsonBody = Encoding.UTF8.GetString(response.RequestInformation.Request);

You can find other useful properties in RequestInformation for debugging.

I like to take it a step further than bsarkar suggests and eliminate the need for a roundtrip altogether:

var client = new ElasticClient();

var seriesSearch = new SearchDescriptor<Series>();
seriesSearch.Filter(f => f
    .Term<Role>(t => t.ReleasableTo.First(), Role.Visitor))
    .SortDescending(ser => ser.EndDate)
    .Size(1));

string searchJson = Encoding.UTF8.GetString(client.Serializer.Serialize(seriesSearch));

Note that your ElasticClient doesn't need any connection properties, so you have no dependency on an ES node.

Really easily. If this is my code that searches:

var results = client.Search<SearchItem>(s => s.AllIndices()
    .Query(q =>
            q.Term(p => p.LastName, searchItem.LastName)
            && q.Term(p => p.FirstName, searchItem.FirstName)
            && q.Term(p => p.ApplicationCode, searchItem.ApplicationCode)
            )
    .Size(1000)
    );
var list = results.Documents.ToList();

I then set a breakpoint on the line above. Then, in Visual Studio Immediate Window, I enter this:

?results.ConnectionStatus

and it gives me this:

{StatusCode: 200, 
    Method: POST, 
    Url: http://localhost:9200/_all/searchitem/_search, 
    Request: {
  "size": 1000,
  "query": {
    "bool": {
      "must": [
        {
          "term": {
            "lastName": {
              "value": "carr"
            }
          }
        },
        {
          "term": {
            "firstName": {
              "value": "adrian"
            }
          }
        }
      ]
    }
  }
}

Hope this helps.

NEST is Baroque of .NET APIs. For 2.1+ on call level:

IElasticClient client = new ElasticClient();
var searchDescriptor = new SearchDescriptor<Series>();
var query = Query<Series>.Term(...);
var pretty = query.ToPrettyString(query);
var json = client.ToRawRequest(searchDescriptor.Query(descriptor => query));

On configuration level:

    var settings = new ConnectionSettings()
                     .PrettyJson().DisableDirectStreaming()
                     .OnRequestCompleted(details=> Debug.WriteLine(Encoding.UTF8.GetString(details.RequestBodyInBytes)));

On response level look into CallDetails.RequestBodyInBytes.

Used extensions:

    /// <summary>
    /// Converts search to raw JSON request for debugging.
    /// </summary>
    /// <typeparam name="T">The type.</typeparam>
    /// <param name="self">The self.</param>
    /// <param name="searchDescriptor">The search descriptor.</param>
    /// <returns>The string.</returns>
    public static string ToRawRequest<T>(this IElasticClient self, SearchDescriptor<T> searchDescriptor) where T : class
    {
        using (var output = new MemoryStream())
        {
            self.Serializer.Serialize(searchDescriptor, output);
            output.Position = 0;
            var rawQuery = new StreamReader(output).ReadToEnd();
            return rawQuery;
        }
    }

    /// <summary>
    /// Prints query into string.
    /// </summary>
    /// <param name="self">The self.</param>
    /// <returns>The value.</returns>
    public static string ToPrettyString(this QueryContainer self)
    {
        using (var settings = new ConnectionSettings())
        {
            var visitor = new DslPrettyPrintVisitor(settings);
            self.Accept(visitor);
            return visitor.PrettyPrint.Replace(Environment.NewLine, string.Empty);
        }                                                                         
    }