feat: add file output support for AI agents

README.md

@@ -7,7 +7,7 @@ Generate <img src="https://mermaid.js.org/favicon.svg" height="14"/> [mermaid](h
 
 - Fully support all features and syntax of `Mermaid`.
 - Support configuration of `backgroundColor` and `theme`, enabling large AI models to output rich style configurations.
-- Support exporting to `png`, `svg`, and `mermaid` formats, with validation for `Mermaid` to facilitate the model's multi-round output of correct syntax and graphics.
+- Support exporting to `base64`, `svg`, `mermaid`, and `file` formats, with validation for `Mermaid` to facilitate the model's multi-round output of correct syntax and graphics. Use `outputType: "file"` to automatically save PNG diagrams to disk for AI agents.
 
 <img width="720" alt="mcp-mermaid" src="https://mermaid.js.org/header.png" />
 

__tests__/tools/mermaid.json

@@ -22,9 +22,9 @@
       },
       "outputType": {
         "type": "string",
-        "enum": ["png", "svg", "mermaid"],
-        "description": "The output type of the diagram. Can be 'png', 'svg' or 'mermaid'. Default is 'png'.",
-        "default": "png"
+        "enum": ["base64", "svg", "mermaid", "file"],
+        "description": "The output type of the diagram. Can be 'base64', 'svg', 'mermaid', or 'file'. Default is 'base64'. 'base64' returns PNG image as base64 encoded string. 'file' will save the PNG image to disk and return the file path.",
+        "default": "base64"
       }
     },
     "required": ["mermaid"],

src/server.ts

@@ -1,3 +1,6 @@
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
 import { Server } from "@modelcontextprotocol/sdk/server/index.js";
 import {
   CallToolRequestSchema,
@@ -58,7 +61,7 @@ function setupToolHandlers(server: Server): void {
           );
         }
 
-        const { mermaid, theme, backgroundColor, outputType = "png" } = args;
+        const { mermaid, theme, backgroundColor, outputType = "base64" } = args;
         const { id, svg, screenshot } = await renderMermaid(
           mermaid as string,
           theme as string,
@@ -85,6 +88,39 @@ function setupToolHandlers(server: Server): void {
             ],
           };
         }
+        if (outputType === "file") {
+          if (!screenshot) {
+            throw new McpError(
+              ErrorCode.InternalError,
+              "Failed to generate screenshot for file output.",
+            );
+          }
+
+          // Create a unique filename with timestamp and random suffix
+          const timestamp = new Date().toISOString().replace(/[:.]/g, "-");
+          const randomSuffix = Math.random().toString(36).substring(2, 8);
+          const filename = `mermaid-${timestamp}-${randomSuffix}.png`;
+
+          // Use current working directory to save the file
+          const filePath = path.resolve(process.cwd(), filename);
+
+          try {
+            fs.writeFileSync(filePath, screenshot);
+            return {
+              content: [
+                {
+                  type: "text",
+                  text: `Mermaid diagram saved to file: ${filePath}`,
+                },
+              ],
+            };
+          } catch (fileError) {
+            throw new McpError(
+              ErrorCode.InternalError,
+              `Failed to save file: ${fileError instanceof Error ? fileError.message : "Unknown file error"}`,
+            );
+          }
+        }
         return {
           content: [
             {

src/tools/index.ts

@@ -23,12 +23,12 @@ C-->D;.`)
     .optional()
     .default("white"),
   outputType: z
-    .enum(["png", "svg", "mermaid"])
+    .enum(["base64", "svg", "mermaid", "file"])
     .describe(
-      "The output type of the diagram. Can be 'png', 'svg' or 'mermaid'. Default is 'png'.",
+      "The output type of the diagram. Can be 'base64', 'svg', 'mermaid', or 'file'. Default is 'base64'. 'base64' returns PNG image as base64 encoded string. 'file' will save the PNG image to disk and return the file path.",
     )
     .optional()
-    .default("png"),
+    .default("base64"),
 });
 
 export const tool = {