MCP Builder

Here's the MCP server for PostgreSQL access:

Tools:

1. query_database — Execute read-only SQL queries

   • Params: query (string, required), limit (number, default 100)
   • Validation: Rejects queries containing INSERT, UPDATE, DELETE, DROP (read-only enforcement)
   • Returns: JSON array of row objects

2. list_tables — List all tables with column info

   • Params: schema (string, default 'public')
   • Returns: Table names with column names, types, and nullable status

3. describe_table — Get detailed schema for one table

   • Params: table_name (string, required)
   • Returns: Columns, types, constraints, indexes, foreign keys

Security:

• Connection uses a read-only database role (no write permissions at DB level)
• Query timeout: 10 seconds max
• Row limit enforced at 1,000 max regardless of parameter

Installation:

// claude_desktop_config.json
{"mcpServers": {"postgres": {"command": "node", "args": ["path/to/server.js"], "env": {"DATABASE_URL": "postgresql://readonly:pass@localhost/mydb"}}}}

Shall I generate the full implementation?

Resources expose data that agents can read (like files or API responses). Here's how to add one:

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";

const server = new McpServer({ name: "my-server", version: "1.0.0" });

// Static resource — always available
server.resource("config", "app://config", async () => ({
  contents: [{
    uri: "app://config",
    mimeType: "application/json",
    text: JSON.stringify(getAppConfig())
  }]
}));

// Dynamic resource template — parameterized
server.resource("user", "app://users/{id}", async (uri) => {
  const id = uri.pathname.split("/").pop();
  const user = await getUser(id);
  return {
    contents: [{
      uri: uri.href,
      mimeType: "application/json",
      text: JSON.stringify(user)
    }]
  };
});

When to use resources vs tools: Resources are for data the agent reads as context (like config files, documentation). Tools are for actions the agent performs (like running queries, creating records). If the agent needs to read it before deciding what to do, it's a resource.