Parties to the Paris Agreement have submitted nationally determined contributions (NDCs) stating their mitigation goals. NDCs vary considerably among countries in length, format and content. Despite the depth of information in NDCs, existing research has focused on mitigation targets, which occupy a small fraction of texts. We undertake systematic analysis of the full textual content of all countries’ NDC documents using natural language processing, allowing the classification of information and objective identification of differences in aims, strategies and policies. Seven broad topic groups emerge, such as development, implementation, and stakeholders, along with 21 constituent topics with sustainable development being the largest. We find that parties devoting a larger share of their NDC to core mitigation topics tend to have more ambitious emission reduction targets. Our results warrant deeper consideration of NDC content to establish best practices, ensuring communication of concrete policies to improve credibility and transparency of national climate plans.