The agglomeration of digital enterprises serves as a crucial foundation for building a modern industrial system and acts as the core engine driving high-quality economic development in China. Public data openness has emerged as a critical institutional arrangement for unlocking the value of data and advancing the development of the digital industry. However, existing research rarely integrates public data openness and digital enterprise agglomeration into a unified analytical framework to systematically examine how public data openness drives the agglomeration of digital enterprises at the micro level. Using panel data from 297 prefecture-level cities in China from 2009 to 2022, this study takes the launch of government data platforms as a quasi-natural experiment, constructs a multi-period difference-in-differences (DID) model, and empirically tests the impact of public data openness on the agglomeration of digital enterprises and its mechanisms after identifying digital enterprises using the BERT model. The results show that: (1) Public data openness significantly enhances the level of digital enterprise agglomeration, and this conclusion remains robust after a series of tests. (2) Heterogeneity analysis indicates that the promoting effect of public data openness on digital enterprise agglomeration is more pronounced in cities with a better business environment and higher household consumption levels. Regarding public data categories, the opening of social livelihood data, economic data, and digital industry data significantly improves digital enterprise agglomeration, whereas the opening of public service data has a negative effect. (3) Mechanism analysis reveals that public data openness enhances digital enterprise agglomeration through three channels: expanding market demand for digital products, fostering the development of the digital innovation ecosystem, and accelerating the accumulation of digital human capital. Compared with existing studies, this paper makes three main contributions. First, this paper examines the impact of public data openness on digital enterprise agglomeration from both government and market perspectives, complementing the evaluation of public data openness policies at the micro-enterprise level. Second, it systematically clarifies three transmission mechanisms through which public data openness affects digital enterprise agglomeration and identifies the boundary conditions of this effect, thereby enriching industrial agglomeration theory in the context of the digital economy. Third, it improves the measurement framework by optimizing the identification of digital enterprises using the BERT model and by refining the measurement of digital product market demand using Baidu Index data, thereby correcting the biases inherent in traditional measurement approaches. The findings of this study reveal the underlying logic of how public data openness drives the agglomeration of digital enterprises at the micro level. These findings provide empirical evidence for deepening market-oriented reforms of data factors and improving the public data openness system in China. They also offer decision-making references for local governments to formulate differentiated support policies for the digital industry and cultivate characteristic digital industry clusters under the “Data Element ×” Action Plan.