SUMMARY: A host of formal, textual languages for modeling cellular processes have recently emerged, but their simulation tools often require an installation process which can pose a barrier for use. Bio Simulators is a framework for easy online deployment of simulators, providing a uniform web-based user interface to a diverse pool of tools. The framework is demonstrated through two plugins based on the KaSim Kappa simulator, one running directly in the browser and another running in the cloud. AVAILABILITY: Web tool: bsims.azurewebsites.net. KaSim client side simulator: github.com/NicolasOury/KaSimJS. KaSim cloud simulator: github.com/mdpedersen/KaSimCloud. CONTACT: [email protected] or [email protected] SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.