Avanti Fellows PostgreSQL MCP Server

Instructions

Args:
    table_name: Name of the table
    schema_name: Schema name (default: public)
    where: Optional WHERE clause (without 'WHERE' keyword)

Returns:
    JSON with count

Implementation Reference

• mcp_postgres/server.py:205-230 (handler)

  The handler function for the 'count_rows' MCP tool. It is registered via the @mcp.tool() decorator. Constructs and executes a safe COUNT(*) query on the specified table, optionally with a validated WHERE clause, and returns the row count as JSON.

  @mcp.tool()
  async def count_rows(table_name: str, schema_name: str = "public", where: str = None) -> str:
      """Count rows in a table, optionally with a WHERE clause.
  
      Args:
          table_name: Name of the table
          schema_name: Schema name (default: public)
          where: Optional WHERE clause (without 'WHERE' keyword)
  
      Returns:
          JSON with count
      """
      sql = f'SELECT COUNT(*) as count FROM "{schema_name}"."{table_name}"'
  
      if where:
          # Basic validation - only allow read operations in WHERE
          if not is_read_only(f"SELECT * FROM t WHERE {where}"):
              return json.dumps({"error": "Invalid WHERE clause"})
          sql += f" WHERE {where}"
  
      try:
          async with get_connection() as conn:
              row = await conn.fetchrow(sql)
              return json.dumps({"count": row["count"]})
      except Exception as e:
          return json.dumps({"error": str(e)})