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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"ConvertFrom-Json silently throws away duplicated keys with identical casing","articleBody":"If the JSON contains duplicate keys with the same casing, then  only the last key is used and the others are silently thrown away. The code in `JsonObject.cs` [here](https://github.com/PowerShell/PowerShell/blob/50f6667bdb0739a315f13b3dd013dc0fb96103cb/src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/JsonObject.cs#L103) actually caters for this case and would throw an error but it never gets to that stage because `JsonConvert.DeserializeObject` [here](https://github.com/PowerShell/PowerShell/blob/50f6667bdb0739a315f13b3dd013dc0fb96103cb/src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/JsonObject.cs#L62) does not throw when there are duplicate keys and simply decides to take the last one.\r\n\r\nSteps to reproduce\r\n------------------\r\n\r\n```powershell\r\n'{ \"key\":\"value1\", \"key\":\"value2\" }' | ConvertFrom-Json\r\n```\r\n\r\nExpected behavior\r\n-----------------\r\n\r\nEither a warning that duplicated keys were disregarded or an error stating that duplicate keys are not allowed unless e.g something like. a `-Force` switch is used. Given that this would be a breaking change, it will probably have to be a warning.\r\n\r\nActual behavior\r\n---------------\r\nOnly the last key is used when there are duplicate keys\r\n```powershell\r\nkey\r\n---\r\nvalue2\r\n```\r\n\r\nEnvironment data\r\n----------------\r\n\r\n\u003c!-- provide the output of $PSVersionTable --\u003e\r\n\r\n```powershell\r\n\u003e $PSVersionTable\r\nName                           Value\r\n----                           -----\r\nPSVersion                      6.0.0-beta.8\r\nPSEdition                      Core\r\nGitCommitId                    v6.0.0-beta.8-20-g0d5a6fbd71c31043d0eda82f7b0e2d4fb0431322\r\nOS                             Microsoft Windows 10.0.15063\r\nPlatform                       Win32NT\r\nPSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}\r\nPSRemotingProtocolVersion      2.3\r\nSerializationVersion           1.1.0.1\r\nWSManStackVersion              3.0\r\n\r\n```\r\n","author":{"url":"https://github.com/bergmeister","@type":"Person","name":"bergmeister"},"datePublished":"2017-10-22T20:21:10.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":12},"url":"https://github.com/5199/PowerShell/issues/5199"}