OP here. I wrote this implementation to deeply understand the mechanics behind HNSW (layers, entry points, neighbor selection) without relying on external libraries. While PHP isn't the typical choice for vector search engines, I found it surprisingly capable for this use case, especially with JIT enabled on PHP 8.x. It serves as a drop-in solution for PHP monoliths that need semantic search features without adding the complexity of a separate service like Qdrant or Pinecone. If you want to jump straight to the code, the open-source repo is here: https://github.com/centamiv/vektor Happy to answer any questions about the implementation details!