Mermaid-Grammer-Inspector

Instructions

Implementation Reference

• src/check.ts:17-47 (handler)

  Core handler logic for the 'check' tool: validates input, writes to temp file, and invokes Mermaid parser.

  export const checkMermaid = async (text: string): Promise<ParseResult> => {
  	// Input validation
  	if (typeof text !== "string") {
  		return {
  			status: ParseStatus.FAIL,
  			message: "Input must be a string",
  		};
  	}
  
  	// Check for empty or whitespace-only content
  	if (!text.trim()) {
  		return {
  			status: ParseStatus.FAIL,
  			message: "Input cannot be empty or contain only whitespace",
  		};
  	}
  
  	const inputFilePath = path.join(__dirname, "input.mmd");
  
  	try {
  		fs.writeFileSync(inputFilePath, text, { encoding: "utf-8" });
  		return await parseMermaid();
  	} catch (error) {
  		const errorMessage =
  			error instanceof Error ? error.message : "File write failed";
  		return {
  			status: ParseStatus.FAIL,
  			message: `Unable to write temporary file: ${errorMessage}`,
  		};
  	}
  };

• src/index.ts:34-52 (registration)

  Registers the MCP 'check' tool with name, description, Zod input schema, and wrapper execute handler.

  server.addTool({
  	name: "check",
  	description:
  		"Check if the text is a valid mermaid diagram. Returns an empty string if valid, otherwise returns the error message.",
  	parameters: z.object({
  		text: z.string(),
  	}),
  	execute: async (args) => {
  		try {
  			const { status, message } = await checkMermaid(args.text);
  			return status === ParseStatus.SUCCESS ? "" : message || "Unknown error";
  		} catch (error) {
  			const errorMessage =
  				error instanceof Error ? error.message : "Unexpected error occurred";
  			console.error("Error in check tool:", errorMessage);
  			return `Internal error: ${errorMessage}`;
  		}
  	},
  });

• src/index.ts:38-40 (schema)

  Zod schema defining the input parameter 'text' for the 'check' tool.

  parameters: z.object({
  	text: z.string(),
  }),

• src/parse.ts:65-90 (helper)

  Helper function that runs the mmdc CLI to parse/validate the Mermaid diagram syntax.

  export const parseMermaid = (
  	inputFile: string = "input.mmd",
  	outputFile: string = "output.svg",
  ): Promise<ParseResult> => {
  	return new Promise((resolve) => {
  		const inputPath = path.join(__dirname, inputFile);
  		const outputPath = path.join(__dirname, outputFile);
  
  		exec(
  			`npx mmdc -i ${inputPath} -o ${outputPath}`,
  			(err, _stdout, stderr) => {
  				if (err) {
  					const errorOutput = stderr || err.message || "";
  					const filteredMessage = filterErrorOutput(errorOutput);
  					resolve({
  						status: ParseStatus.FAIL,
  						message: filteredMessage || err.message || "Unknown error",
  					});
  					return;
  				}
  
  				resolve({ status: ParseStatus.SUCCESS });
  			},
  		);
  	});
  };

• src/parse.ts:11-19 (schema)

  Type definitions for ParseStatus enum and ParseResult interface used throughout the check tool chain.

  export enum ParseStatus {
  	SUCCESS,
  	FAIL,
  }
  
  export interface ParseResult {
  	status: ParseStatus;
  	message?: string;
  }