Many efforts have been made to standardize indicators that aim to assess, monitor and compare sustainable development at different territorial levels. Arguments in favor and against the need to design common indicators are many and highly contested, which is why this article intends to contribute to the study on the outcomes for cities that put common local indicators to practice. This article aims to discuss the constraints and achievements of standardizing these indicators. It first explores and analyzes the efforts of European institutions and research projects supported by them towards the harmonization of local sustainable development indicators. In a second stage, it analyzes a Portuguese initiative that uses common indicators to benchmark sustainable development across cities and municipalities – ECOXXI. Evidence is gathered from two case study municipalities, Oeiras and Cascais, that have applied this indicator set, through a review and analysis of documents and semi-structured interviews with relevant public officers. The lessons learned point to major benefits on the sharing of guidelines and the delivery of a top-down but flexible indicator approach in the absence of national or European official guidelines. The main constraints are linked to issues of communication and to limited political support and use of such indicators.