SYNTHIA Retrosynthesis Software is a cloud-based, software-as-a-service (SaaS) platform that helps chemists rapidly design robust synthetic routes using expert-coded rules curated by chemists and engineered by computer scientists, enabling discovery of novel pathways for both new and published target molecules; the technology has been developed over 21 years and searches a catalog of more than 12 million commercially available starting materials and building blocks. It is purpose-built for computer-aided synthesis design (CASD/CASP), accelerating route scouting while improving speed, safety, and cost efficiency across discovery and development workflows. Scientists can run Automatic, Step-by-Step, Similar Molecules, or Shared Path Library analyses, then view up to 50 synthetic pathways per target and filter results by number of steps, pathway similarity, starting-material cost, and protecting-group use; each pathway includes typical reaction conditions, illustrative publications, and options to export or share for collaboration. Users can tailor searches with preset or custom configurations to include preferred reactions, exclude reagents or classes, set price limits, and start from commercial or in-house inventories—streamlining from target input to shopping list generation of buyable building blocks. SYNTHIA supports greener route design by allowing users to avoid hazardous reagents and seek safer alternatives as part of configurable search criteria. For integration at scale, the SYNTHIA API offers two modalities: the Full Retro API returns detailed pathway data (reaction SMILES and names, literature references, prices and CAS numbers of starting materials, and pathway scores), while the Synthetic Accessibility Score (SAS) API provides a 0–10 complexity score to triage large virtual libraries; both are designed to plug into KNIME, Pipeline Pilot, Jupyter, and similar workflows. The platform runs on an ISO 27001–certified secure cloud infrastructure, supporting enterprise-grade data protection for cheminformatics workflows. Across medicinal, discovery, and process chemistry teams, SYNTHIA is used to save time, reduce costs, and expand idea space by proposing alternative, often more atom-efficient disconnections and ranked pathways that complement literature precedent and in-house expertise. Access options include a free individual trial and tiered licenses (including batch analysis and custom inventory features for advanced needs), making it easy to pilot the software and scale with project demand.