# How to Build a Semantic Search Engine for E-Commerce in Python > Source: > Published: 2026-07-16 06:29:49+00:00 Building a semantic search engine for an e-commerce catalogue doesn't require a team of PhDs or a six-figure cloud budget. In this tutorial, I'll walk you through a production-ready pipeline using open-source tools: sentence-transformers for embedding, FAISS for vector indexing, and FastAPI for serving. The core insight is that semantic search isn't magic — it's just good engineering wrapped around a pre-trained language model. We'll start by setting up a product embedding pipeline that transforms your catalogue (title, description, category, attributes) into dense vectors. The key architectural decision is whether to embed each product as a single vector or to use late interaction models like ColBERT that preserve token-level detail. For most e-commerce use cases with fewer than 1 million SKUs, single-vector embedding with sentence-transformers' `all-MiniLM-L6-v2` offers the best balance of speed and accuracy. The entire indexing pipeline — from CSV export to queryable vector index — runs in under 100 lines of Python. The re-ranking layer is where most tutorials stop and real-world systems begin. Pure vector similarity doesn't understand your business: it doesn't know that out-of-stock items should be deprioritised, that high-margin products should float up, or that a customer's purchase history should influence results. I'll show you how to build a hybrid scoring function that blends semantic relevance (cosine similarity), business rules (margin, inventory), and personalisation signals (user embedding) into a single ranked result set that returns in under 100ms. Canonical: [https://alteglobal.ai/insights/ecommerce-ai-automation-personalisation-fulfillment/](https://alteglobal.ai/insights/ecommerce-ai-automation-personalisation-fulfillment/)