Comparison
BM25 vs Semantic Search
BM25 and Semantic Search are both common AI/LLM terms but cover different ideas. Here is a quick side-by-side.
When you would reach for BM25
BM25 comes up when the question is fundamentally about agents & tools.
A codebase search where BM25 finds every file containing the exact function name; vector alone often missed them.
When you would reach for Semantic Search
Semantic Search comes up when the question is fundamentally about agents & tools.
Searching "cars under 10k" matches "vehicles below ten thousand dollars."
Frequently asked
What is the difference between BM25 and Semantic Search?
BM25: BM25 is the classical keyword-based ranking algorithm: a refined TF-IDF that scores documents by query-term frequency, document length, and corpus-wide rarity. The keyword side of hybrid search. Semantic Search: Semantic search ranks documents by meaning rather than keyword match, using embedding similarity. "Affordable laptops" can match "cheap notebooks" even with no overlapping words.
When should I use BM25 vs Semantic Search?
BM25 is the right concept when you are focused on agents & tools. Semantic Search applies when you are focused on agents & tools.
Are BM25 and Semantic Search the same thing?
No. BM25 is agents & tools; Semantic Search is agents & tools. They are related but address different parts of the AI stack.