import pandas as pd
import matplotlib.pyplot as plt

def plot_sales_tool(file_path: str) -> str:
    df = pd.read_csv(file_path)
    if 'Month' not in df.columns or 'Sales' not in df.columns:
        return "Missing 'Month' or 'Sales' columns."
    plt.figure(figsize=(10, 6))
    plt.plot(df['Month'], df['Sales'], marker='o')
    plt.xticks(rotation=45)
    plt.title("Sales Trend")
    plt.savefig("sales_plot.png")
    return "Generated sales_plot.png"