This paper shows an alternative method to evaluate sustainable development and corporate social responsibility (CSR) practices based on the opinions of companies' stakeholders expressed on Twitter. An application of the method is performed with the Inditex textile group. This paper shows two important findings: (a) knowledge about companies' CSR practices and stakeholders opinions can be obtained using big data to analyse CSR information about the company on online social networks; and (b) there are important differences between the contents of the sustainability report of a company and the CSR opinions of its stakeholders on the internet. These findings have benefits for the company's stakeholders, who will be able to know the CSR practices of a company in a more objective way, and for the company, which will be able to improve its CSR performance and communication strategy, as well as the stakeholder engagement.