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

# Resource keys

In our API, resources can be identified by either an internal ID or a user-defined reference. We refer to these identifiers collectively as "keys".

## Key Types

1. **ID**: Internally set UUID
   * Example: `123e4567-e89b-12d3-a456-426614174000`

2. **Reference (ref)**: User-defined, unique identifier
   * Examples:
     * Accounts: `internal:revenue:fx`
     * Ledgers: `ledger:customer_a`
     * Transaction: `txn:invoice_123`
     * Asset Move: `83c6be5d-ebb8-41fc-8d12-d1f8ec4e2a90`

## Usage in API Endpoints

When a path parameter is described as a "key" in the documentation, you can use either an ID or a reference.

### Path Parameter Syntax

* For IDs: `id:$id` or simply `$id`
  * Example: `/ledgers/id:123e4567-e89b-12d3-a456-426614174000`
  * Example: `/ledgers/123e4567-e89b-12d3-a456-426614174000`

* For references: `ref:$ref`
  * Example: `/ledgers/ref:ledger:customer_a`

> Note: If no prefix is given, the system defaults to interpreting the value as an ID.

### Key Points

* References must be unique within their resource type.
* The `ref:` prefix is required when using a reference in path parameters.
* The `id:` prefix is optional for IDs in path parameters.