generate_chart

Instructions

Generate a chart/visualization from tabular data.
Returns chart as base64-encoded PNG for display.

Args:
    file_path: Path to CSV or SQLite file
    chart_type: Type of chart - 'bar', 'line', 'scatter', 'histogram', 'pie', 'box'
    x_column: Column for X-axis (not needed for histogram/pie)
    y_column: Column for Y-axis values
    group_by: Optional column for grouping/coloring
    title: Chart title (auto-generated if not provided)
    output_format: 'base64' (default) or 'file' (saves to data/charts/)

Returns:
    Dictionary containing chart data as base64 or file path

Implementation Reference

• src/mcp_tabular/server.py:963-1115 (handler)

  The generate_chart tool handler. Loads data, validates inputs, uses matplotlib to create various chart types (bar, line, scatter, histogram, pie, box), and returns either base64 PNG or saves to file.

  @mcp.tool()
  def generate_chart(
      file_path: str,
      chart_type: str,
      x_column: str | None = None,
      y_column: str | None = None,
      group_by: str | None = None,
      title: str | None = None,
      output_format: str = "base64",
  ) -> dict[str, Any]:
      """
      Generate a chart/visualization from tabular data.
      Returns chart as base64-encoded PNG for display.
      
      Args:
          file_path: Path to CSV or SQLite file
          chart_type: Type of chart - 'bar', 'line', 'scatter', 'histogram', 'pie', 'box'
          x_column: Column for X-axis (not needed for histogram/pie)
          y_column: Column for Y-axis values
          group_by: Optional column for grouping/coloring
          title: Chart title (auto-generated if not provided)
          output_format: 'base64' (default) or 'file' (saves to data/charts/)
      
      Returns:
          Dictionary containing chart data as base64 or file path
      """
      df = _load_data(file_path)
      
      valid_types = ['bar', 'line', 'scatter', 'histogram', 'pie', 'box']
      if chart_type not in valid_types:
          raise ValueError(f"Unknown chart_type: {chart_type}. Use: {valid_types}")
      
      # Set up the figure with a clean style
      plt.style.use('seaborn-v0_8-whitegrid')
      fig, ax = plt.subplots(figsize=(10, 6))
      
      # Generate chart based on type
      if chart_type == 'histogram':
          if y_column is None:
              numeric_cols = _get_numeric_columns(df)
              if not numeric_cols:
                  raise ValueError("No numeric columns found for histogram")
              y_column = numeric_cols[0]
          
          ax.hist(df[y_column].dropna(), bins=30, edgecolor='black', alpha=0.7, color='#4C72B0')
          ax.set_xlabel(y_column)
          ax.set_ylabel('Frequency')
          auto_title = f'Distribution of {y_column}'
          
      elif chart_type == 'pie':
          if x_column is None:
              cat_cols = df.select_dtypes(include=['object', 'category']).columns.tolist()
              if not cat_cols:
                  raise ValueError("No categorical columns found for pie chart")
              x_column = cat_cols[0]
          
          value_counts = df[x_column].value_counts().head(10)
          colors = plt.cm.Set3(np.linspace(0, 1, len(value_counts)))
          ax.pie(value_counts.values, labels=value_counts.index, autopct='%1.1f%%', colors=colors)
          auto_title = f'Distribution of {x_column}'
          
      elif chart_type == 'box':
          if y_column is None:
              numeric_cols = _get_numeric_columns(df)
              if not numeric_cols:
                  raise ValueError("No numeric columns found for box plot")
              y_column = numeric_cols[0]
          
          if group_by and group_by in df.columns:
              groups = df[group_by].unique()[:10]  # Limit to 10 groups
              data = [df[df[group_by] == g][y_column].dropna() for g in groups]
              ax.boxplot(data, labels=groups)
              ax.set_xlabel(group_by)
          else:
              ax.boxplot(df[y_column].dropna())
          ax.set_ylabel(y_column)
          auto_title = f'Box Plot of {y_column}'
          
      elif chart_type in ['bar', 'line', 'scatter']:
          if x_column is None or y_column is None:
              raise ValueError(f"Both x_column and y_column are required for {chart_type} chart")
          
          if x_column not in df.columns:
              raise ValueError(f"x_column '{x_column}' not found")
          if y_column not in df.columns:
              raise ValueError(f"y_column '{y_column}' not found")
          
          if group_by and group_by in df.columns:
              for name, group in df.groupby(group_by):
                  if chart_type == 'bar':
                      ax.bar(group[x_column].astype(str), group[y_column], label=str(name), alpha=0.7)
                  elif chart_type == 'line':
                      ax.plot(group[x_column], group[y_column], label=str(name), marker='o', markersize=4)
                  else:  # scatter
                      ax.scatter(group[x_column], group[y_column], label=str(name), alpha=0.7)
              ax.legend(title=group_by, loc='best')
          else:
              if chart_type == 'bar':
                  # For bar charts, aggregate if needed
                  if df[x_column].dtype == 'object':
                      agg = df.groupby(x_column)[y_column].mean()
                      ax.bar(agg.index.astype(str), agg.values, color='#4C72B0', alpha=0.7)
                  else:
                      ax.bar(df[x_column].astype(str).head(50), df[y_column].head(50), color='#4C72B0', alpha=0.7)
              elif chart_type == 'line':
                  ax.plot(df[x_column], df[y_column], marker='o', markersize=4, color='#4C72B0')
              else:  # scatter
                  ax.scatter(df[x_column], df[y_column], alpha=0.6, color='#4C72B0')
          
          ax.set_xlabel(x_column)
          ax.set_ylabel(y_column)
          auto_title = f'{y_column} by {x_column}'
          
          # Rotate x labels if needed
          if df[x_column].dtype == 'object' or chart_type == 'bar':
              plt.xticks(rotation=45, ha='right')
      
      # Set title
      ax.set_title(title or auto_title, fontsize=14, fontweight='bold')
      
      plt.tight_layout()
      
      # Save chart
      if output_format == 'file':
          charts_dir = _PROJECT_ROOT / 'data' / 'charts'
          charts_dir.mkdir(parents=True, exist_ok=True)
          timestamp = datetime.now().strftime('%Y%m%d_%H%M%S')
          filename = f'{chart_type}_{timestamp}.png'
          filepath = charts_dir / filename
          plt.savefig(filepath, dpi=150, bbox_inches='tight')
          plt.close()
          
          return {
              "chart_type": chart_type,
              "file_path": str(filepath.relative_to(_PROJECT_ROOT)),
              "absolute_path": str(filepath),
          }
      else:
          # Return as base64
          buffer = io.BytesIO()
          plt.savefig(buffer, format='png', dpi=150, bbox_inches='tight')
          plt.close()
          buffer.seek(0)
          image_base64 = base64.b64encode(buffer.getvalue()).decode('utf-8')
          
          return {
              "chart_type": chart_type,
              "format": "png",
              "encoding": "base64",
              "image_data": image_base64,
              "display_note": "Use this base64 string to display the image",
          }