The Nationally Determined Contributions (NDCs) are key documents providing the starting point for increasingly ambitious ‘pledge-and-review’ cycles leading to the implementation of the Paris Agreement. However, current NDCs often lack consistent and transparent targets and indicators to ensure their in-country realisation and their monitoring, tracking, and reporting in compliance with the current climate change regime. This is particularly true for developing countries, where resources and capacity to define and implement climate action plans are still largely lacking among practitioners. To tackle this problem, this essay proposes a framework for NDCs development focusing on the practitioners’ – i.e., modellers and expert analysts – uptake of open science practices, particularly concerning open-source tools and open data, via capacity-building initiatives as a first step towards transparent and accountable NDCs delivery and implementation to the benefit of national and international climate governance. The framework is applied to the case study of Costa Rica, to test its relevance and applicability.