> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usegandalf.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Core concepts in Gandalf

> Learn the core concepts behind Gandalf: snapshots, Review Changes, provider-backed actions, agent-native marketplace sources, evidence, and the trust contract.

Gandalf's model is built on a small set of primitives. Understanding these concepts makes the CLI and TUI predictable: what gets scanned, what can be mutated, what has to be previewed first, and what safety net protects you when something goes wrong.

<CardGroup cols={2}>
  <Card title="Snapshots" icon="camera" href="/concepts/snapshots">
    Content-backed vs metadata-only captures of your agent state.
  </Card>

  <Card title="Review Changes" icon="eye" href="/concepts/review-changes">
    The mandatory preview before any mutation.
  </Card>

  <Card title="Providers" icon="plug" href="/concepts/providers">
    Only provider-backed rows are actually executable.
  </Card>

  <Card title="Marketplace" icon="store" href="/concepts/marketplace">
    Agent-native source browsing and its limits.
  </Card>

  <Card title="Trust Contract" icon="shield" href="/trust-contract">
    The runtime safety boundaries Gandalf enforces.
  </Card>

  <Card title="Support Matrix" icon="table" href="/reference/support-matrix">
    Exactly what is supported per agent today.
  </Card>
</CardGroup>

## Supporting vocabulary

* **Evidence** is a typed record of a discovered configuration artifact: a config file, an MCP server entry, a permission rule, an env key. Each has a kind, source path, and optional structured value. Scans, snapshots, diffs, and restore plans all speak in evidence.
* **Setup Console** is Gandalf's default TUI screen: a sidebar with Home, Console, Changes, Timeline, and Saves, and Console tabs for Hooks, Plugins, Marketplace, Skills, and MCP Servers.
* **Unified Inventory** is the normalized, cross-agent list of setup rows that the Console renders. It groups skills, hooks, MCP servers, and plugins as global/user rows with compact agent identity, so you never pick an agent picker before you see your setup.
* **Changes-First Home** summarizes drift from the latest supported baselines before you enter inventory browsing or recovery flows. It is read-only: Review opens the detailed environment diff, and rollback still goes through Review Changes before Apply.

## How they fit together

1. `gandalf scan` discovers evidence read-only.
2. `gandalf snapshot create` persists evidence (metadata or content-backed) to the store.
3. `gandalf diff` compares two snapshots (or a snapshot and `current`) as semantic changes plus raw source changes.
4. The TUI and CLI expose actions only when a **provider** can preview and execute them.
5. Every mutation surfaces a **Review Changes** preview first.
6. `gandalf restore` uses a content-backed snapshot as the safety net for rollback.