# Schema reference

Source: https://docs.graphops.xyz/subgraphs/schema-reference

Find the entities, fields, and filters you can query on a specific Subgraph. Every Subgraph has its
own GraphQL schema, so GraphOps does not publish one universal entity reference. This page shows how
to discover a schema and documents the `_meta` fields most Subgraphs share.

## Discover the schema

Use GraphQL introspection, the schema published with the Subgraph project, or the schema map in
[Discover Subgraphs](./guides/discover-public-subgraphs) to discover:

* Entity names.
* Field names and scalar types.
* Relationship fields.
* Generated filters.
* Generated ordering fields.
* Whether full-text search fields are present.

## Introspection query

```graphql
query IntrospectionTypes {
  __schema {
    queryType {
      fields {
        name
      }
    }
    types {
      name
      kind
    }
  }
}

```

Use the same endpoint and authentication method as application queries.

## Metadata reference

Most Subgraphs expose `_meta`:

| Field                     | Meaning                                                |
| ------------------------- | ------------------------------------------------------ |
| `_meta.deployment`        | Deployment serving the query.                          |
| `_meta.block.number`      | Latest indexed block number available to the endpoint. |
| `_meta.block.hash`        | Hash of the indexed block.                             |
| `_meta.hasIndexingErrors` | Whether indexing errors are present.                   |

```graphql
query Metadata {
  _meta {
    deployment
    block {
      number
      hash
    }
    hasIndexingErrors
  }
}

```

## Generated client types

GraphOps does not provide service-level SDKs for Subgraphs. If your application needs generated
types, generate them from the specific Subgraph schema using your GraphQL client toolchain.

## Next steps

* [Query a Subgraph](./guides/query-a-subgraph): Turn the schema into a parameterized query.
* [Paginate results](./guides/paginate-results): Order by a stable field and read large collections.
* [Monitor sync health](./guides/monitor-sync-health): Use `_meta` for freshness and error alerts.