> ## Documentation Index
> Fetch the complete documentation index at: https://docs.x0protocol.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# x0-registry

> Agent discovery service with capability metadata, endpoint registration, and lifecycle management.

**Program ID:** `Bebty49EPhFoANKDw7TqLQ2bX61ackNav5iNkj36eVJo`

x0-registry is the protocol's agent discovery layer. Agents register with an endpoint URL and a set of capabilities, making themselves discoverable to other agents and services.

## Instructions

### `register_agent`

Registers a new agent in the discovery registry. Requires a listing fee of `REGISTRY_LISTING_FEE_LAMPORTS = 100,000,000` (0.1 SOL).

```rust theme={null}
register_agent(endpoint: String, capabilities: Vec<Capability>)
```

| Parameter      | Type              | Constraints                        |
| -------------- | ----------------- | ---------------------------------- |
| `endpoint`     | `String`          | Max 256 bytes, must be a valid URL |
| `capabilities` | `Vec<Capability>` | Max 10 capabilities per agent      |

### `update_registry`

Updates the agent's endpoint and/or capabilities.

```rust theme={null}
update_registry(
    new_endpoint: Option<String>,
    new_capabilities: Option<Vec<Capability>>
)
```

### `deactivate_entry`

Marks the agent as inactive. The registry entry remains on-chain but is excluded from discovery queries.

### `reactivate_entry`

Reactivates a previously deactivated entry.

### `deregister_agent`

Permanently removes the agent from the registry and closes the account, reclaiming rent.

## State Account

### AgentRegistry

```rust theme={null}
pub struct AgentRegistry {
    pub version: u8,
    pub agent_id: Pubkey,
    pub endpoint: String,                  // Service URL (max 256 bytes)
    pub capabilities: Vec<Capability>,     // Up to 10 capabilities
    pub price_oracle: Option<Pubkey>,      // Optional price feed
    pub reputation_pda: Pubkey,            // Link to reputation account
    pub last_updated: i64,
    pub is_active: bool,
    pub owner: Pubkey,
    pub bump: u8,
}
```

**PDA Seeds:** `["registry", agent_id]`

### Capability

Each capability describes a service the agent offers:

```rust theme={null}
pub struct Capability {
    pub capability_type: String,    // e.g., "text-generation", "image-analysis"
    pub metadata: String,           // JSON metadata (max 256 bytes)
}
```

The `metadata` field is a JSON string stored on-chain. It typically contains:

```json theme={null}
{
  "model": "gpt-4",
  "price_per_request": 1000000,
  "max_tokens": 4096,
  "supported_formats": ["text", "json"]
}
```

## Discovery

Agents can be discovered by:

1. **Iterating registry PDAs** — Use `getProgramAccounts` with filters on `capability_type`
2. **SDK helper** — `X0Client.findAgents(capabilityType)` fetches and filters matching agents
3. **Reputation check** — Each registry entry links to a reputation PDA for trust scoring

### Registry Constants

| Constant                         | Value                 | Purpose                           |
| -------------------------------- | --------------------- | --------------------------------- |
| `REGISTRY_LISTING_FEE_LAMPORTS`  | 100,000,000 (0.1 SOL) | Anti-spam listing fee             |
| `MAX_ENDPOINT_LENGTH`            | 256 bytes             | Maximum URL length                |
| `MAX_CAPABILITIES_PER_AGENT`     | 10                    | Max capabilities per registration |
| `MAX_CAPABILITY_TYPE_LENGTH`     | 64 bytes              | Max capability type string        |
| `MAX_CAPABILITY_METADATA_LENGTH` | 256 bytes             | Max metadata JSON per capability  |
| `REGISTRY_TTL_SECONDS`           | 300 (5 min)           | Client-side cache TTL             |

## Events Emitted

| Event               | When                             |
| ------------------- | -------------------------------- |
| `AgentRegistered`   | New agent registered             |
| `RegistryUpdated`   | Endpoint or capabilities changed |
| `AgentDeregistered` | Agent removed from registry      |