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

# Entities

> Define reusable data structures (entities) to standardize sample data and improve template maintainability.

Entities are reusable data structure definitions — schemas for the data your templates expect. They help keep sample data consistent, validate structure early, and document expected formats.

## Prerequisites

* Understanding of [Placeholders](/guides/templates-placeholders) and [Sample data](/guides/templates-sample-data)
* Basic knowledge of JSON and data types

## What is an entity?

An entity defines:

* Field names
* Field types (string, number, boolean, object, array)
* Required vs. optional fields
* Nested structures and array item types

**Entity (schema):** Defines the shape (e.g. "Customer" with `id`, `name`, `email`, `vip_status`).

**Sample data (instance):** Actual values that match that shape (e.g. `{ "customer": { "id": "CUST-123", "name": "John Doe", ... } }`).

## Create an entity

1. Go to **Entities** in the sidebar
2. Click **Create Entity**
3. Set **Name** (e.g. "Customer", "Order") and **Description**
4. Add fields: **Field name**, **Type** (string, number, boolean, object, array), **Required** (yes/no)
5. For nested objects, add child fields; for arrays, set the item type
6. Save the entity

## Use entities with templates

* Attach an entity to a template (or to sample data) so the expected structure is documented and validated
* Sample data that matches the entity ensures placeholders like `{{customer.name}}` have the right shape
* Reuse the same entity across multiple templates for consistency

## Benefits

* **Consistency** — Same structure across templates
* **Validation** — Catch missing or wrong types early
* **Documentation** — Self-documenting expected data format
* **Reusability** — Define once, use in many templates

## Next steps

<CardGroup cols={2}>
  <Card title="Placeholders" icon="code" href="/guides/templates-placeholders">
    Use entity-shaped data in placeholders.
  </Card>

  <Card title="Sample data" icon="database" href="/guides/templates-sample-data">
    Create and manage sample data sets for templates.
  </Card>

  <Card title="Table blocks" icon="table" href="/guides/templates-table-blocks">
    Display tabular data in messages (experimental).
  </Card>
</CardGroup>