You can use TabStar's KeyFinder to analyze your guitar tabs and find and set their key. When a song's key is set the Key Information panel shows a Validate Song button. Validating songs will highlight all the notes in red which are not in the chosen key. You can toggle this feature on and off as you chose. Song Validation is available to holders of the Full Account.

The picture below shows a song which has its key set and has Song Validation set to on. The Chord Boxes show the notes which are outside the key with a red border, and also the open string indicators which are not in key. The Tablature Grid also shows the notes which are not in the chosen key with a red border.

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