# Core Concepts

Context Nest is built on a small set of composable concepts. Understanding these gives you the full picture of how vaults work.

## Architecture

```
┌────────────────────────────────────────────────────────┐
│                    Context Nest Vault                  │
│                                                        │
│  ┌──────────┐  ┌──────────┐  ┌──────────────────────┐ │
│  │  Nodes   │  │ Sources  │  │   Packs              │ │
│  │ (docs,   │  │ (live    │  │   (curated bundles   │ │
│  │  refs,   │  │  data    │  │    with agent        │ │
│  │  etc.)   │  │  feeds)  │  │    instructions)     │ │
│  └────┬─────┘  └────┬─────┘  └──────────┬───────────┘ │
│       │              │                   │             │
│       └──────────────┼───────────────────┘             │
│                      │                                 │
│              ┌───────▼────────┐                        │
│              │   Selectors    │                        │
│              │  tag, type,    │                        │
│              │  pack, status  │                        │
│              └───────┬────────┘                        │
│                      │                                 │
│              ┌───────▼────────┐                        │
│              │   Resolver     │                        │
│              │  Evaluates     │                        │
│              │  queries,      │                        │
│              │  returns docs  │                        │
│              └───────┬────────┘                        │
│                      │                                 │
│              ┌───────▼────────┐                        │
│              │   Versioning   │                        │
│              │  Hash chains,  │                        │
│              │  checkpoints   │                        │
│              └────────────────┘                        │
└────────────────────────────────────────────────────────┘
```

## Key Concepts

| Concept | What it is |
|---------|-----------|
| [Vault Structure](https://nest.promptowl.ai/d/promptowl-documents/protocol/concepts/vault-structure) | How files and directories are organized |
| [Node Types](https://nest.promptowl.ai/d/promptowl-documents/protocol/concepts/node-types) | The 8 types of documents a vault can contain |
| [Frontmatter](https://nest.promptowl.ai/d/promptowl-documents/protocol/concepts/frontmatter) | YAML metadata that governs every document |
| [Context Index](https://nest.promptowl.ai/d/promptowl-documents/protocol/concepts/context-index) | `context.yaml` — the machine-readable vault manifest |
| [Selectors](https://nest.promptowl.ai/d/promptowl-documents/protocol/selectors/overview) | Composable query grammar for filtering documents |
| [Context Packs](https://nest.promptowl.ai/d/promptowl-documents/protocol/context-packs/overview) | Curated bundles of documents with agent instructions |
| [Addressing](https://nest.promptowl.ai/d/promptowl-documents/protocol/addressing/overview) | `contextnest://` URI scheme for cross-referencing |
| [Source Nodes](https://nest.promptowl.ai/d/promptowl-documents/protocol/source-nodes/overview) | Documents that instruct agents to fetch live data |
| [Versioning](https://nest.promptowl.ai/d/promptowl-documents/protocol/versioning/overview) | Hash chains, keyframes, diffs, and checkpoints |