The gold tools require different things to unlock them, and some are more difficult than others to achieve, since most of them are not based on how many times you use them, but on achieving specific objectives in areas related to each tool. The gold machete is usually the first tool you'll unlock, since it is based on how much grass you cut. The others will take longer, but you can find clues to what you might need to accomplish by reviewing all of the stats at the mayor's desk in the Town Hall.
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Barbara
Unicorn
Last Day of Work