Schema Filtering

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:

SCHEMAS=public,analytics isthmus

Or in your MCP client config:

{
  "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

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.

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:

# AI sees only public and analytics
SCHEMAS=public,analytics

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

Getting Started

Client Setup

Features

Security

Architecture

Schema Filtering

Configuration

Behavior

When `SCHEMAS` is not set (default)

When `SCHEMAS` is set

Use cases

Example

​Configuration

​Behavior

​When SCHEMAS is not set (default)

​When SCHEMAS is set

​Use cases

​Example

Configuration

Behavior

When `SCHEMAS` is not set (default)

When `SCHEMAS` is set

Use cases

Example