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You might want to ask this on the Spring Development Tools forum. I've not noticed major problems in Groovy syntax highlighting for a long time, so I'm wondering whether you have the latest Groovy Eclipse plugin installed. Go to STS' About dialog and check what version of Groovy Eclipse is installed (you should just need to click on the Groovy logo). I'm on 2.1.0.xx-20101020-1000-e36-release.