The main difference between Proxycurl (Nubela) and Coresignal is the amount of data. While the former boasts 464M+ people and 20M+ company records, the latter provides 718M+ employees, 102M+ company, and 437M+ job posting records.
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If that wasn't enough, there's no information about Proxycurl API. Last but not least, Proxycurl's data comes from fewer sources and covers fewer locations.
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To sum up, Coresignal is a great Proxycurl alternative.