Accelerated Innovation

Using BM25 for Accurate Keyword Retrieval

By /

Using BM25 for Accurate Keyword Retrieval

Description

This capability focuses on using BM25-a ranking function based on term frequency and inverse document frequency-to retrieve relevant content based on keyword matches. It enables product and engineering teams to improve keyword-based search by tuning for document importance, term rarity, and query-document relevance.

Why it's Important

Accurate keyword-based retrieval is foundational for enterprise GenAI systems that rely on structured search or hybrid RAG pipelines. BM25 provides a transparent and efficient method for ranking documents using keyword matches-critical for use cases where deterministic behavior, explainability, or compliance is required. When implemented well, BM25 strengthens baseline retrieval performance, improves user trust in results, and enhances the performance of downstream LLM generation by reducing irrelevant or noisy context. It also provides a mature, tunable framework for teams that are just beginning to experiment with GenAI and need fast, interpretable wins.

Why it's Challenging @ Scale

  • Query variability across domains: BM25 can struggle when keywords vary widely across business units, making it hard to tune parameters globally.
  • Limited semantic flexibility: Unlike vector-based retrieval, BM25 does not capture meaning or synonyms-leading to missed matches in context-rich queries.
  • Sparse metadata usage: Many organizations underutilize available metadata fields, reducing BM25’s ability to disambiguate similar documents.
  • Poor document hygiene: BM25 assumes reasonably clean and well-structured documents-unstructured or noisy data reduces its effectiveness.
  • Tuning across pipelines: Optimal BM25 settings may differ for retrieval vs. re-ranking workflows, creating challenges in hybrid systems.

Complexity

Medium: While BM25 is a well-established algorithm, effectively applying it at scale requires disciplined content preprocessing, thoughtful parameter tuning, and integration into broader GenAI workflows.

Ready to accelerate your GenAI journey?

Click below to validate your access

Let's go!

Taking Action

Though most organizations begin their GenAI journey with significant knowledge gaps, there are targeted actions that can be taken to accelerate the process. Select your group’s current maturity, based on your assessment results, and act today.

  • Explore Key Concepts & Best Practices: Complete the Enterprise GenAI Retrieval workshop (2 hrs.) to understand foundational key concepts and explore applied best practices
  • Introducing Enterprise GenAI Retrieval Concepts
  • Linking Retrieval with Application Experience
  • Modeling Document Contexts and Sections
  • Embedding with Metadata for Precision
  • Defining KPIs for Retrieval Effectiveness
  • Define Your Action Plan: Outline concrete, prioritized steps your organization will take to implement GenAI Strategy.
  • Align on your Current State and define your Target State
  • Create an actionable enablement plan
  • Define target timeline and measures of success
  • Deliver Quick Wins: Small, high-impact GenAI projects that can demonstrate tangible value in a short time frame.
  • Launch a BM25 Pilot: Apply BM25 to 1-2 internal retrieval use cases and assess performance gains over baseline keyword search.
  • Tune BM25 Parameters: Optimize k1 and b values to improve relevance scoring across representative document sets.
  • Benchmark Against Vector Search: Compare BM25 results to dense retrieval on the same queries to highlight tradeoffs in accuracy and interpretability.
  • Complete one or more of our Deep Dive Courses: Begin exploring key concepts and best practices, including:
  • A Deep Dive into RAG Re-Ranking
  • A Deep Dive into Advanced RAG Re-Ranking Methods
  • A Deep Dive into Agent-Based Response Refinement for High-Quality GenAI Responses
  • A Deep Dive into Agent-based Report Generation for High-Quality GenAI Responses
  • Nail It Before You Scale It: Assess and optimize your solution or process before adopting it at scale
  • Assess Your Proposed Solution or Process: Evaluate how BM25 is currently used in pilot implementations and measure retrieval effectiveness.
  • Define in-scope Processes and Guardrails: Clarify where keyword-based retrieval is appropriate, and how BM25 integrates with vector or hybrid models.
  • Close any Data or Measurement Gaps: Collect click-through data, feedback, and failure cases to refine BM25 scoring and relevance thresholds.
  • Define Your Adoption & Scaling Plan: Create a structured roadmap for how GenAI solutions will be rolled out across teams, workflows, or business units
  • Define Your Phased Implementation Plan: Identify high-impact search and retrieval workflows to prioritize BM25 deployment.
  • Build Awareness and Finalize Enablers: Share BM25 tuning guides, example configs, and query templates with platform and product teams.
  • Operationalize Your Comms Plan: Communicate key results, tuning updates, and rollout status to stakeholders and developers.
  • Formalize Your Best Practices: Document and standardize what’s working to ensure consistent, scalable success across teams and use cases
  • Publish BM25 Tuning Playbooks: Capture parameter settings, preprocessing rules, and sample queries as internal standards.
  • Create Standard BM25 Config Templates: Provide reusable configuration files for teams to apply BM25 in consistent ways across platforms.
  • Embed BM25 in Hybrid Design Patterns: Define best practices for using BM25 in conjunction with vector or re-ranking methods.
  • Accelerate Your Adoption: Intensify efforts to embed GenAI across your organization by expanding use cases, increasing user engagement, and removing adoption barriers
  • Extend Keyword Retrieval to New Use Cases: Scale BM25 to support audit logs, policy search, compliance queries, and structured content lookups.
  • Equip Teams with Self-Serve Tools: Package BM25 search into APIs, SDKs, or plug-ins that internal teams can easily deploy and experiment with.
  • Run Retrieval Performance Clinics: Offer deep-dive sessions to help product teams troubleshoot or enhance keyword relevance.
  • Celebrate Your Wins: Publicly acknowledge team accomplishments to build and sustain adoption momentum
  • Highlight Keyword Retrieval Success Stories: Share where BM25 dramatically improved search precision or content access.
  • Showcase Before-and-After Impact: Compare baseline and BM25-enhanced retrieval to show measurable improvements.
  • Recognize Contributors to Tuning Excellence: Celebrate the engineers and data scientists refining your retrieval configurations.
  • Streamline & Embed: Integrate GenAI into core workflows while eliminating friction points to make usage seamless and routine
  • Embed BM25 in Core Platforms: Make BM25 the default retrieval option in internal knowledge portals and developer search tools.
  • Use Real-Time Query Scoring: Dynamically adjust BM25 parameters based on user behavior, query type, or document source.
  • Standardize Retrieval Interfaces: Unify APIs and services so teams can easily switch between or combine keyword and semantic search.
  • Leverage Automation: Using GenAI-powered tools and workflows to streamline repetitive tasks, enhance operational efficiency, and reduce manual effort
  • Auto-Tune BM25 Settings: Deploy scripts or services that monitor relevance performance and adjust parameters accordingly.
  • Flag and Fix Low-Quality Results: Use retrieval QA tools to identify weak matches and recommend improvements.
  • Integrate BM25 into Hybrid Pipelines: Seamlessly combine BM25 outputs with vector results in ensemble or re-ranking configurations.
  • Evolve & Further Accelerate: Continuously refine GenAI strategies based on insights and outcomes, while expanding into more complex or high-impact use cases
  • Monitor Retrieval Effectiveness Across Use Cases: Track long-term performance and user satisfaction with BM25-powered search.
  • Apply Learnings to Other Capabilities: Extend BM25-style scoring concepts to new modalities like table retrieval or structured data queries.
  • Benchmark Keyword Retrieval Against Industry Leaders: Use precision and recall metrics to assess your competitive positioning.

Key "Watchouts"

  • Over-indexing on keyword recall: High recall can come at the expense of precision-ensure relevance is validated through testing.
  • Neglecting query and document hygiene: Poorly formatted text, stop words, or inconsistent tokenization can undermine BM25 effectiveness.
  • Treating BM25 as “set and forget”: BM25 requires occasional retuning as documents, use cases, and query types evolve.
  • Failing to benchmark results: Without systematic evaluation, it’s hard to know whether BM25 is truly improving retrieval outcomes.
  • Using BM25 in isolation: In complex workflows, combining BM25 with vector or hybrid approaches often yields better results.

Targeted Benefits

  • Improved search transparency: BM25 provides interpretable scoring based on keyword relevance, aiding debugging and trust.
  • Stronger performance in compliance use cases: Deterministic keyword matching supports auditability and explainability.
  • Faster time-to-value: BM25 is easy to deploy and tune-making it ideal for rapid prototyping or bootstrapping GenAI solutions.
  • Optimized hybrid retrieval workflows: BM25 can complement vector search by anchoring results with exact keyword matches.
  • Lower infrastructure complexity: BM25 doesn’t require GPU acceleration or embedding models-reducing system overhead.

Looking to Move Faster, and 'Go Bigger'?

Contact us to explore additional acceleration resources or support.
Click here
Eddie
Accelerated Innovation

Hi, I'm Eddie 👋

Ask me anything about AI concepts, best practices, Accelerated Innovation solutions, or how to get started.