Validating web config files

If you have edited a web config file and want to check it for duplicates and punctuation errors before putting it back, paste the contents into the config validator at https://elmah.io/tools/config-validator/ and run it.

The elmah.io config validator showing a Validate button and a Valid with warnings result, with an Errors tab and a Warnings tab; the warning flags duplicate connection string names

It reports any errors and warnings in the file. In this example it returns no errors and one warning, flagging two connection strings that share the same name, which is the kind of mistake that is easy to introduce when editing the file by hand.