mesh‑tree is a Node.js library that provides fast, programmatic access to the full Medical Subject Headings (MeSH) ontology stored in a LevelGraph database. It offers a rich set of functions for retrieving descriptor IDs, terms, tree numbers, hierarchical relationships (parents, children, ancestors, common ancestors), Wikipedia summaries, pharmacological actions, and Schema.org mappings, and can be used both in‑process or via a multilevel client/server setup. The package is aimed at developers, bioinformaticians, and researchers who need to query or traverse MeSH data in biomedical applications.