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

# Schema Filtering

> Control which database schemas are visible to the AI.

By default, Isthmus exposes all non-system schemas in your database. The `SCHEMAS` environment variable lets you restrict visibility to only the schemas you choose.

## Configuration

Set the `SCHEMAS` environment variable to a comma-separated list:

```bash theme={null}
SCHEMAS=public,analytics isthmus
```

Or in your MCP client config:

```json theme={null}
{
  "mcpServers": {
    "isthmus": {
      "command": "isthmus",
      "env": {
        "DATABASE_URL": "postgres://user:pass@localhost:5432/mydb",
        "SCHEMAS": "public,analytics"
      }
    }
  }
}
```

## Behavior

### When `SCHEMAS` is not set (default)

All non-system schemas are visible. System schemas (`pg_catalog`, `information_schema`, `pg_toast`) are always excluded.

The AI can discover and query any user-created schema in the database.

### When `SCHEMAS` is set

Only the listed schemas are visible. All tools respect this filter:

| Tool             | Effect                                                           |
| ---------------- | ---------------------------------------------------------------- |
| `discover`       | Only returns the allowed schemas and their tables                |
| `describe_table` | Only works for tables in allowed schemas                         |
| `query`          | Queries can reference any table, but schema discovery is limited |

<Warning>
  Schema filtering restricts **discovery**, not SQL execution. A query like `SELECT * FROM hidden_schema.secret_table` will still execute if the database user has access. For true access control, use PostgreSQL roles and grants. See [Security](/docs/security).
</Warning>

## Use cases

* **Multi-tenant databases** — expose only the tenant's schema
* **Staging vs. production** — hide staging schemas from the AI
* **Large databases** — reduce noise by focusing on the schemas that matter
* **Compliance** — limit discovery of schemas containing sensitive data

## Example

A database with schemas `public`, `analytics`, `staging`, and `internal`:

```bash theme={null}
# AI sees only public and analytics
SCHEMAS=public,analytics

# AI sees everything except system schemas
# (just don't set SCHEMAS)
```