context-fundamentalslisted

# Context Engineering Fundamentals Context is the complete state available to a language model at inference time: system instructions, tool definitions, retrieved documents, message history, and tool outputs. Understanding context fundamentals is prerequisite to all other context engineering skills. ## When to Use / Not Use **Use when:** - Designing new agent systems or modifying existing architectures - Onboarding to context engineering concepts - Reviewing context-related design decisions - Debugging unexpected agent behavior that may relate to context structure **Do NOT use when:** - Diagnosing context failures or degradation -> use `context-degradation` - Compressing or summarizing context -> use `context-compression` - KV-cache optimization or context partitioning -> use `context-optimization` - File-based context patterns or scratch pads -> use `filesystem-context` ## Decision Tree ``` What do you need to understand about context? ├── What goes INTO context │ ├── System instructions / identity -> System Prompts (§Anatomy) │ ├── Available actions -> Tool Definitions (§Anatomy) │ ├── External knowledge -> Retrieved Documents (§Anatomy) │ ├── Conversation so far -> Message History (§Anatomy) │ └── Action results -> Tool Outputs (§Anatomy) ├── How context is CONSUMED │ ├── Attention mechanics / budget -> Attention Budget (§Attention) │ ├── Position encoding limits -> Position Encoding (§Attention) │ └── Quality vs quantity trade-offs -> Quality vs Quan