Its actually open-source. Here is the repo: https://github.com/mireklzicar/doi-reference-extractor

APIs Used OpenCitations API (v2)

Endpoint: https://opencitations.net/index/api/v2/references/ Purpose: Retrieves a list of all references from a paper by its DOI Data format: JSON containing cited DOIs and metadata DOI Content Negotiation

Endpoint: https://doi.org/{DOI} Purpose: Fetches metadata and formatted citations for DOIs Formats: BibTeX, RIS, CSL JSON, RDF XML, etc. Implements CSL (Citation Style Language) for text-based citations Local Citation Style Files

Purpose: Provides access to thousands of citation styles Storage: Pre-generated JSON files with style information