Ask-Docs Architecture: Semantic Embeddings or Keyword Search for a SaaS Help Center?

Short answer: for an ask-your-docs feature in a multi-tenant SaaS help center, start with embeddings over document chunks, retain keyword search for exact identifiers, and add reranking only when retrieval evaluation shows that the first-stage ordering is weak. The architecture is simple: ingest tenant-scoped chunks, embed them, store the vectors in a managed index, retrieve a small candidate set, and give only those matches to the answer model. The important marketplace constraint is less glamorous: every retrieval and model call must carry a tenant identifier into metering, or the team will know the total bill while remaining unable to explain which storefront created it. Don't begin with a vendor. Begin with the miss you can tolerate. How should a SaaS help center combine semantic search, embeddings, and keyword search? Semantic retrieval handles the normal language mismatch between a customer's question and the documentation. A user may ask how to “change the shop owner,” while the source chunk says “transfer account administration.” Keyword matching sees different tokens; embeddings map both query and chunks into vectors and can retrieve text with related meaning. That is the decisive reason to use embeddings for support questions, not fashion and not an assumption that vectors make every search problem better. Keyword search still earns a narrow, valuable lane. Error codes, plan names, API fields, invoice identifiers, and product-specific phrases often need literal matching. PAYMENT_1042 is not a semantic concept that should be softened into something approximately related. For a beginner implementation, run vector retrieval as the default and merge an exact-match result when the query contains one of those identifiers; don't build a many-stage ranking system before the corpus supplies evidence that you need one. Chunk boundaries matter because retrieval returns chunks, not abstract documents. Split by meaningful document structure, retain the page title and s