Read-Only Database Access for Agents via MCP

Give an agent safe SQL querying through an MCP server connected with a read-only database role.

Enforce safety in the database, not only in the prompt.

1. Create a read-only role

CREATE ROLE agent_ro LOGIN PASSWORD 'change-me';
GRANT CONNECT ON DATABASE app TO agent_ro;
GRANT USAGE ON SCHEMA public TO agent_ro;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO agent_ro;
ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO agent_ro;
ALTER ROLE agent_ro SET statement_timeout = '5s';

Better still: point it at a read replica and grant only on views that exclude sensitive columns.

2. MCP config

{
  "mcpServers": {
    "postgres": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-postgres",
               "postgresql://agent_ro:change-me@localhost:5432/app"]
    }
  }
}

The reference Postgres server is archived (github.com/modelcontextprotocol/servers-archived) and the npm package @modelcontextprotocol/server-postgres is marked deprecated ("no longer supported"); the config above still shows the pattern, but for production use a maintained Postgres MCP server, and keep the same read-only-role principle.

Failure modes

• The reference server package is deprecated; plan a maintained replacement.
• Expensive queries can load production; use a replica and statement_timeout.
• Views that include sensitive columns leak data; grant only on safe views.

Markdown version: /blueprints/mcp-postgres-readonly.md

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