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Back to Learn
KnowledgeLayer 2Retrieval Architecture

Hybrid Search

You built an internal knowledge base. Uploaded your docs. Added AI search.

Someone searches for "PTO policy" and gets nothing. You know the document exists.

You check. It is called "Time Off Guidelines." The AI had no idea they meant the same thing.

Your search was smart about meaning OR exact words. Never both.

8 min read
intermediate
Relevant If You're
Building AI-powered search for internal docs
Getting wrong or missing results from your knowledge base
Wondering why your search misses obvious matches

INTERMEDIATE - Requires embeddings and basic search infrastructure to be in place.

Where This Sits

Category 2.3: Retrieval Architecture

2
Layer 2

Intelligence Infrastructure

Chunking StrategiesCitation & Source TrackingEmbedding Model SelectionHybrid SearchQuery TransformationRelevance ThresholdsReranking
Explore all of Layer 2
What It Is

Two search methods that cover each other's blind spots

Keyword search finds exact matches. If someone searches "Q4 2024 revenue report," it finds documents with those exact words. Fast, precise, predictable. But completely blind to meaning. "Quarterly earnings summary" returns nothing.

Semantic search understands meaning. It knows "PTO policy" and "time off guidelines" are the same concept. But it can struggle with specifics. Search for "Form W-2" and it might return general tax documents instead of the actual form.

Hybrid search runs both. Keyword search catches exact matches. Semantic search catches meaning matches. The results merge into a single ranked list. When one method fails, the other compensates.

Keyword search is dumb but precise. Semantic search is smart but fuzzy. Together, they catch what neither would find alone.

The Lego Block Principle

Hybrid search solves a universal problem: how do you find something when you might describe it differently than how it was labeled?

The core pattern:

Use multiple detection methods with different failure modes. When one method misses, another catches it. The combination is more reliable than either alone.

Where else this applies:

Hiring and resumes - Match exact job titles AND similar experience descriptions.
Customer support routing - Match known categories AND understand novel phrasings of problems.
Asset and resource lookup - Find exact codes AND similar descriptions.
Meeting notes search - Match exact names mentioned AND topics discussed in different words.
🎮 Interactive: See What Each Method Finds

Search and watch keyword, semantic, and hybrid find different things

Click a search query. Watch which documents each method finds (or misses).

Each query demonstrates a different blind spot. Try them all.

Keyword (BM25)

2
results found
Employee Vacation Policy85%
Company Holiday Schedule 202430%

Finds exact word matches only

Semantic (Vector)

4
results found
Employee Vacation Policy90%
Time Off Guidelines88%
Company Holiday Schedule 202465%

Finds similar meaning, different words

Hybrid (Combined)

4
results found
Employee Vacation Policy
KS
Company Holiday Schedule 2024
KS
Time Off Guidelines
S

K = keyword found, S = semantic found

For "vacation days": Semantic wins: Doc is titled "Time Off Guidelines"

Try it: Click each query above and watch which documents each method finds. Notice how keyword and semantic have different blind spots.
How It Works

Two searches, one answer

Keyword Search (BM25)

Exact word matching

Counts how often query words appear in documents. Weights rare words higher than common ones. "Form W-2" matches documents containing exactly those words.

Pro: Perfect for specific terms, names, codes, IDs
Con: Completely blind to synonyms and rephrasing

Semantic Search (Vector)

Meaning-based matching

Converts query and documents to embeddings. Finds documents with similar meaning even if words differ. "Time off request" matches "PTO policy."

Pro: Understands intent and finds conceptual matches
Con: Can miss exact terms, especially technical jargon

Fusion & Ranking

Combining the results

Both searches return scored results. Reciprocal Rank Fusion (RRF) combines them: items that rank high in both get boosted. Items that only one method found still appear.

Pro: Best of both worlds, few blind spots
Con: Slightly more complexity and compute cost
Connection Explorer

"Where's the vacation policy?" instantly answered

A team member needs the PTO policy but searches "vacation days." Your document is titled "Time Off Guidelines." Without hybrid search, they find nothing. With this flow, they get the right document in under a second, regardless of how they phrase it.

Hover over any component to see what it does and why it's neededTap any component to see what it does and why it's needed

Vector Database
Chunking
Embeddings
Hybrid Search
You Are Here
Reranking
Correct Document Found
Outcome
React Flow
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Press enter or space to select an edge. You can then press delete to remove it or escape to cancel.
Foundation
Data Infrastructure
Intelligence
Understanding
Outcome

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Upstream (Requires)

Embedding GenerationVector DatabasesChunking Strategies

Downstream (Enables)

RerankingRelevance Thresholds
Common Mistakes

What breaks when hybrid search goes wrong

Weighting keyword too heavily for a messy knowledge base

Your internal docs were written by 12 different people over 5 years. Nobody used consistent terminology. Keyword search finds almost nothing because "vacation time," "PTO," "time off," and "leave" are all different words for the same thing.

Instead: Start with 70% semantic, 30% keyword. Tune based on what your users actually search for.

Weighting semantic too heavily for technical content

Someone searches for "error code E-4523" and gets documents about general troubleshooting instead of the specific error. Semantic search understood "error" but missed the exact code that matters.

Instead: Detect when queries contain codes, IDs, or exact phrases. Boost keyword weight for those queries.

Skipping hybrid because "semantic search is smarter"

You invested in embeddings and vector search. Keyword search feels like a step backward. But users keep reporting missing results for exact names, form numbers, and technical terms.

Instead: Smart and precise are different qualities. You need both. Add keyword search even if it feels redundant.

What's Next

Now that you understand hybrid search

You know how to combine keyword and semantic search. The natural next step is understanding how to re-order those combined results for even better accuracy.

Recommended Next

Reranking

How to re-order search results for better precision

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