Context Optimization Skill

This skill provides methodologies and best practices for maximizing context window efficiency, reducing token costs, and improving the performance of LLM-based agentic workflows.

1. Prompt Cache Alignment

To maximize Key-Value (KV) cache hits, prioritize stability in the early parts of the prompt.

• Static Prefixes: Design system prompts to remain identical across agent turns.
• Tool Order: Sort tool definitions alphabetically or by frequency of use. Keep this ordering constant.
• Prefix Consistency: Reserve the top 70% of the KV cache for global system instructions and tool definitions.
• Avoid Dynamic Data: Move dynamic session-specific data (dates, current file list) to the end of the context window.

2. Semantic Pruning & AST Compaction

Reduce unnecessary data before sending it to the model.

• Removal of Non-Essentials: Strip comments, debug logs, and unused boilerplate code.
• AST Compaction: Convert deep code structures into simplified, representative summaries or pseudocode.
• Whitespace Stripping: Use minification for configuration files (JSON, YAML) and standard code.
• Irrelevant Body Dropping: Replace large, irrelevant function bodies with docstrings or signatures if the model doesn't need to reason about the implementation details.

3. Lost-in-the-Middle Mitigation

LLMs often suffer from recall degradation for information in the center of the context window.

• Boundary Priority: Place high-priority constraints, critical instructions, and schema definitions at the very beginning (Head) or the very end (Tail) of the context.
• Sandwich Strategy: If critical information must be in the middle, sandwich it between two clear, high-level summary points that repeat its purpose.

4. Sliding Windows & Recursive Summarization

Manage long-running conversations without exceeding token thresholds.

• Sliding Window: Keep only the N most recent turns for immediate interaction.
• Recursive Summarization: Periodically collapse historical turns into a compressed "Session State Summary".
• State Archiving: Store older, less relevant interactions in a side-car file (e.g., archive.md) that the agent can read only when necessary.

5. Token Budget Allocation

Implement a disciplined token distribution:

Category	Typical %	Goal
System Prompt	10-15%	Definition of role & constraints
Tool Definitions	15-20%	Capability exposure
Interaction History	30-40%	Context for current turn
Reserved (Drafting)	25-45%	Headroom for generation

6. Context Freshness Decisions

Determine when to act on history:

• Summarize: When history exceeds 50% of the token budget and requires long-term context.
• Truncate: When history is irrelevant to the current task or contains repetitive technical noise.
• Archive: When information must be preserved (e.g., decisions, ADRs) but is not needed for the immediate turn.

7. Measuring Cache Hit Rate

Continuous improvement relies on telemetry.

• Monitoring: Track Cache Hit Rate (CHR) metrics provided by the API provider.
• Iteration: Analyze sessions with low CHR. Are the system prompts shifting? Is tool definition order inconsistent?
• Optimization Loop:
  1. Measure performance per turn.
  2. Identify volatility in the prefix.
  3. Refactor static content to improve cache stability.
  4. Re-measure.

Best Practices Checklist

• Does my system prompt remain stable across requests?
• Are tools sorted consistently?
• Is critical information pinned to the Head or Tail?
• Have I pruned unused code/data from the ingestion stream?
• Is there an automated summarization step for history?