Using Fiddler and Excel 07 to debug web services
Random problem with a relatively innovative discovery method.
I am working with an app that sends and receives buckets of data via web services. In one particular case, I was receiving a couple of purchase orders' worth of details and attempting to turn the XML into a DataSet. The DataSet contains 2 tables tied by a relationship which we need later on in the app to improve performance. Basically, the error I was getting was a duplicate key error inside of the dataset when I tried to apply the relationship. So, how to find the problem...?
First I used Fiddler. This nice little tool grabbed the XML being returned from the web service call and allowed me to save it as a text file. Internet Explorer was able to see the XML with no trouble, but since there were over a hundred PO detail lines (which translates to way too many lines to try to read in IE).
Fiddler - 
XMLResponse - 
Enter Excel. Using the Export to Excel function from IE, I was able to construct a nice little table in Excel. Then, using the easier than ever PivotTable functionality, I was able to spot the problem record in seconds...
Excel Table - 
Excel PivotTable - 
Now that I knew which order was causing the problem, it was pretty simple to execute the stored proc in the database and find out that the pricing table was messed up - resulting in 2 records returned for one of the items. Fix the data, fix the problem.