The Self-assessment tool for IPSPs created by the DIAMAS project is available athttps://diamas.fecyt.es/. The Self-assessment tool for IPSPs is designed to provide an intuitive and effective user experience in managing and self-assessing the level of compliance of institutional publishers (IPs) with the Extensible Quality Standard in Institutional Publishing (EQSIP) for Diamond Open Access (D3.2 of DIAMAS project) and sustainability parameters. Users are institutional publishers (IPs). Service providers (SPs) have been excluded due to their different nature, as stablished in EQSIP. The tool is made up of two parallel instances: one for EQSIP self-assessment, and a second one for sustainability parameters self-assessment. Upon completion, users receive a report with their scores. An Administrator role has been created to verify and edit content, manage categories (core components), and create new editions based on the tool's needs.This role is played by the Spanish Foundation for Science and Technology (FECYT).The code of the software has been licensed with a European Union Public License EUPL v1.2. It is publicly available at https://github.com/FECYT/DIAMAS.