QuickChart MCP Server

Instructions

Implementation Reference

• src/index.ts:243-273 (handler)

  Handler for the 'download_chart' tool. Parses arguments, generates chart config and URL using helpers, downloads the image with axios, saves to outputPath using fs.promises.writeFile, and returns success message.

  case 'download_chart': {
    try {
      const { config, outputPath } = request.params.arguments as { 
        config: Record<string, unknown>;
        outputPath: string;
      };
      const chartConfig = this.generateChartConfig(config);
      const url = await this.generateChartUrl(chartConfig);
      
      const response = await axios.get(url, { responseType: 'arraybuffer' });
      const fs = await import('fs');
      await fs.promises.writeFile(outputPath, response.data);
      
      return {
        content: [
          {
            type: 'text',
            text: `Chart saved to ${outputPath}`
          }
        ]
      };
    } catch (error: any) {
      if (error instanceof McpError) {
        throw error;
      }
      throw new McpError(
        ErrorCode.InternalError,
        `Failed to download chart: ${error?.message || 'Unknown error'}`
      );
    }
  }

• src/index.ts:200-213 (schema)

  Input schema for download_chart tool, defining required 'config' object and 'outputPath' string.

  inputSchema: {
    type: 'object',
    properties: {
      config: {
        type: 'object',
        description: 'Chart configuration object'
      },
      outputPath: {
        type: 'string',
        description: 'Path where the chart image should be saved'
      }
    },
    required: ['config', 'outputPath']
  }

• src/index.ts:197-214 (registration)

  Tool registration entry in ListTools response, including name, description, and input schema.

  {
    name: 'download_chart',
    description: 'Download a chart image to a local file',
    inputSchema: {
      type: 'object',
      properties: {
        config: {
          type: 'object',
          description: 'Chart configuration object'
        },
        outputPath: {
          type: 'string',
          description: 'Path where the chart image should be saved'
        }
      },
      required: ['config', 'outputPath']
    }
  }

• src/index.ts:79-142 (helper)

  Key helper function used by download_chart to validate and construct the ChartConfig from the input config argument.

  private generateChartConfig(args: any): ChartConfig {
    const { type, labels, datasets, title, options = {} } = args;
    
    this.validateChartType(type);
  
    const config: ChartConfig = {
      type,
      data: {
        labels: labels || [],
        datasets: datasets.map((dataset: any) => ({
          label: dataset.label || '',
          data: dataset.data,
          backgroundColor: dataset.backgroundColor,
          borderColor: dataset.borderColor,
          ...dataset.additionalConfig
        }))
      },
      options: {
        ...options,
        ...(title && {
          title: {
            display: true,
            text: title
          }
        })
      }
    };
  
    // Special handling for specific chart types
    switch (type) {
      case 'radialGauge':
      case 'speedometer':
        if (!datasets?.[0]?.data?.[0]) {
          throw new McpError(
            ErrorCode.InvalidParams,
            `${type} requires a single numeric value`
          );
        }
        config.options = {
          ...config.options,
          plugins: {
            datalabels: {
              display: true,
              formatter: (value: number) => value
            }
          }
        };
        break;
  
      case 'scatter':
      case 'bubble':
        datasets.forEach((dataset: any) => {
          if (!Array.isArray(dataset.data[0])) {
            throw new McpError(
              ErrorCode.InvalidParams,
              `${type} requires data points in [x, y${type === 'bubble' ? ', r' : ''}] format`
            );
          }
        });
        break;
    }
  
    return config;
  }