The **biojs-io-matrix** package is a lightweight Node.js library that parses and writes 2‑dimensional biological score matrices (e.g., PAM substitution matrices). It provides simple functions—`read` for fetching matrix files, `parse` for turning raw text into nested objects, line‑by‑line building, and `export` for converting matrices back to text—making it useful for developers building bioinformatics tools that need to ingest or generate matrix data.