Using the gradual opening of municipal public data platforms across various cities as a quasi-natural experiment, this study empirically examines the impact of public data opening on the quality of analysts’ earnings forecasts. The findings reveal that public data opening significantly reduces analysts’ earnings forecast errors and dispersion, thereby improving the quality of earnings forecasts. Mechanism tests indicate that public data opening enhances the quality of forecasts through both the “information effect”, which increases forward-looking statements and financial information in analyst reports, and the “monitoring effect”, which attracts greater analyst coverage and curbs corporate earnings management. Furthermore, this effect is more pronounced in samples where data openness is more comprehensive or relevant. The improvement in earnings forecast quality due to public data opening is more significant for forecasts made by non-star analysts, companies with lower information transparency, and industries with lower digital technology intensity.