Infracost MCP Server

Instructions

Implementation Reference

• src/tools.ts:310-332 (handler)

  Main handler for 'infracost_diff' tool. Validates args, checks Infracost CLI installation, executes the diff command via executeDiff, and returns the output as MCP content.

  async handleDiff(args: z.infer<typeof DiffSchema>) {
    const isInstalled = await checkInfracostInstalled();
    if (!isInstalled) {
      throw new Error(
        'Infracost CLI is not installed. Please install it from https://www.infracost.io/docs/'
      );
    }
  
    const result = await executeDiff(args);
  
    if (!result.success) {
      throw new Error(result.error || 'Diff command failed');
    }
  
    return {
      content: [
        {
          type: 'text',
          text: result.output || 'Diff completed successfully',
        },
      ],
    };
  }

• src/cli.ts:75-110 (helper)

  Core helper function that executes the 'infracost diff' CLI command with resolved paths and options, captures stdout/stderr/JSON, and returns structured result.

  export async function executeDiff(options: DiffOptions): Promise<CommandResult> {
    try {
      const args = ['diff', '--path', resolve(options.path), '--compare-to', resolve(options.compareTo)];
  
      if (options.format) {
        args.push('--format', options.format);
      }
  
      if (options.outFile) {
        args.push('--out-file', resolve(options.outFile));
      }
  
      const { stdout, stderr } = await execFileAsync('infracost', args, {
        maxBuffer: 10 * 1024 * 1024,
      });
  
      let parsedData;
      if (options.format === 'json' && !options.outFile && stdout.trim()) {
        try {
          parsedData = JSON.parse(stdout);
        } catch (e) {}
      }
  
      return {
        success: true,
        output: options.outFile ? `Output saved to ${options.outFile}` : stdout,
        error: stderr || undefined,
        data: parsedData,
      };
    } catch (error) {
      return {
        success: false,
        error: error instanceof Error ? error.message : 'Unknown error occurred',
      };
    }
  }

• src/tools.ts:21-26 (schema)

  Zod schema defining the input parameters for the infracost_diff tool, used for validation.

  export const DiffSchema = z.object({
    path: z.string().describe('Path to Terraform directory or plan JSON file'),
    compareTo: z.string().describe('Path to baseline Terraform directory or plan JSON file'),
    format: z.enum(['json', 'diff']).optional().describe('Output format'),
    outFile: z.string().optional().describe('Save output to file'),
  });

• src/index.ts:106-133 (registration)

  Tool registration in ListTools handler, including name, description, and input schema (mirroring DiffSchema).

  {
    name: 'infracost_diff',
    description:
      'Show cost differences between two Terraform configurations. Compares baseline and current infrastructure to identify cost changes. Requires infracost CLI to be installed.',
    inputSchema: {
      type: 'object',
      properties: {
        path: {
          type: 'string',
          description: 'Path to current Terraform directory or plan JSON file',
        },
        compareTo: {
          type: 'string',
          description: 'Path to baseline Terraform directory or plan JSON file',
        },
        format: {
          type: 'string',
          enum: ['json', 'diff'],
          description: 'Output format (default: diff)',
        },
        outFile: {
          type: 'string',
          description: 'Save output to a file',
        },
      },
      required: ['path', 'compareTo'],
    },
  },

• src/index.ts:709-712 (handler)

  Dispatch case in main CallToolRequestHandler that parses args with DiffSchema and delegates to InfracostTools.handleDiff.

  case 'infracost_diff': {
    const validatedArgs = DiffSchema.parse(args);
    return await tools.handleDiff(validatedArgs);
  }