Initial LAI MCP server #5

Author: dhuebner

package-lock.json

@@ -14,6 +14,7 @@
     "license": "MIT",
     "workspaces": [
         "packages/langium-ai-tools",
+        "packages/langium-ai-mcp",
         "packages/examples/*"
     ],
     "volta": {

package.json

@@ -8,7 +8,8 @@
         "build": "tsc",
         "start": "node ./dist/index.js",
         "demo": "npm run build && npm run start -- run-langdev && open ./radar-chart.html",
-        "clean": "rimraf ./dist"
+        "clean": "rimraf ./dist",
+        "test": "echo \"No tests yet...\""
     },
     "type": "module",
     "author": {

packages/examples/example-dsl-evaluator/package.json

@@ -0,0 +1,21 @@
+How to try-out:
+
+- `cd packages/langium-ai-mcp`
+- Start MCP server with IO transport `npm run start`
+- Run example client code `npm run cstart` - you should see the tool result containing the errors.
+
+Example usage in Cursor:
+
+- Open Cursor MCP settings
+- Add new server using following setup (user or workspace specific `.cursor/mcp.json` ):
+
+```json
+"mcpServers": {
+    "Langium MCP": {
+        "command": "node",
+        "args": [
+            "~/git/langium-ai/packages/mcp-server/dist/mcp-server.js"
+        ]
+    }
+}
+```

packages/langium-ai-mcp/README.MD

@@ -0,0 +1,52 @@
+{
+    "name": "langium-ai-mcp",
+    "version": "0.0.2",
+    "displayName": "Langium AI - MCP",
+    "publisher": "TypeFox",
+    "description": "MCP server for Langium AI",
+    "repository": {
+        "type": "git",
+        "url": "git+https://github.com/eclipse-langium/langium-ai.git",
+        "directory": "packages/langium-ai-mcp"
+    },
+    "bugs": "https://github.com/eclipse-langium/langium-ai/issues",
+    "type": "module",
+    "main": "dist/mcp-server.js",
+    "private": false,
+    "files": [
+        "dist"
+    ],
+    "scripts": {
+        "clean": "rm -rf ./dist",
+        "build": "npm run clean && tsc",
+        "watch": "tsc -w",
+        "start": "node .",
+        "cstart": "node ./dist/mcp-client.js",
+        "prepare": "npm run build",
+        "test": "vitest run"
+    },
+    "author": {
+        "name": "TypeFox",
+        "url": "https://www.typefox.io"
+    },
+    "keywords": [
+        "langium",
+        "ai",
+        "mcp",
+        "server",
+        "llm"
+    ],
+    "license": "MIT",
+    "dependencies": {
+        "@modelcontextprotocol/sdk": "^1.17.4",
+        "langium-ai-tools": "0.0.2"
+    },
+    "volta": {
+        "node": "20.10.0",
+        "npm": "10.2.3"
+    },
+    "devDependencies": {
+        "typescript": "^5.4.5",
+        "vitest": "^3.0.9"
+    }
+}

packages/langium-ai-mcp/package.json

@@ -0,0 +1,39 @@
+import { Client } from "@modelcontextprotocol/sdk/client/index.js";
+import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";
+import { getDisplayName } from "@modelcontextprotocol/sdk/shared/metadataUtils.js";
+
+const debug = false
+
+const transport = new StdioClientTransport({
+    command: "node",
+    args: [ "./dist/mcp-server.js"]
+});
+
+const client = new Client(
+    {
+        name: "example-client",
+        version: "1.0.0"
+    }
+);
+
+await client.connect(transport);
+
+const tools = await client.listTools();
+console.log("Available tools:", "\n", ...tools.tools.map(t => getDisplayName(t) + "\n"));
+
+const theTool = tools.tools[0];
+if (!theTool) {
+    throw new Error("No tool available");
+}
+
+const result = await client.callTool({
+    name: theTool.name,
+    arguments: {
+        code: 'syntax error'
+    }
+});
+
+console.log("Tool result:", result.content);
+
+// exit the process
+process.exit(0);

packages/langium-ai-mcp/src/mcp-client.ts

@@ -0,0 +1,60 @@
+import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
+import { LangiumEvaluator, type LangiumEvaluatorResultData } from 'langium-ai-tools';
+import { createLangiumGrammarServices } from 'langium/grammar';
+
+import { NodeFileSystem } from 'langium/node';
+import { z } from 'zod';
+
+const server = new McpServer({
+    name: 'langium-mpc-server',
+    version: '1.0.0'
+});
+
+server.registerTool('langium-syntax-checker',
+    {
+        title: 'Langium Evaluator Tool',
+        description: 'Checks Langium code for errors',
+        inputSchema: { code: z.string() }
+    },
+    async ({ code }) => {
+        const validationResult = await validateLangiumCode(code);
+        return {
+            content: [
+                {
+                    type: 'text',
+                    text: validationResult ?? 'The provided Langium code has no issues.'
+                }
+            ]
+        }
+    }
+);
+
+export const langiumEvaluator = new LangiumEvaluator(createLangiumGrammarServices(NodeFileSystem).grammar);
+
+export async function validateLangiumCode(code: string): Promise<string | undefined> {
+    const evalResult = await langiumEvaluator.evaluate(code);
+    if (evalResult.data) {
+        const langiumData = evalResult.data as LangiumEvaluatorResultData;
+        if (langiumData.diagnostics.length > 0) {
+            return langiumData.diagnostics.map(d =>
+                `${asText(d.severity)}: ${d.message} at line ${d.range.start.line + 1}, column ${d.range.start.character + 1}`
+            ).join('\n');
+        }
+    }
+    return undefined;
+}
+
+function asText(severity: number | undefined): string {
+
+    switch (severity) {
+        case 1: return 'Error';
+        case 2: return 'Warning';
+        case 3: return 'Information';
+        case 4: return 'Hint';
+        default: return 'Unknown';
+    }
+}
+
+const transport = new StdioServerTransport();
+await server.connect(transport);

packages/langium-ai-mcp/src/mcp-server.ts

@@ -0,0 +1,32 @@
+import { describe, expect, it } from 'vitest';
+
+import { validateLangiumCode } from '../src/mcp-server';
+
+describe('validateLangiumCode', () => {
+
+
+    it('should return undefined for valid grammar code', async () => {
+        const validCode = `
+                grammar HelloWorld
+                
+                entry Model: persons+=Person*;
+                Person: 'person' name=ID;
+                hidden terminal WS: /\\s+/;
+                terminal ID: /[_a-zA-Z][\\w_]*/;
+            `;
+
+        const result = await validateLangiumCode(validCode);
+        expect(result).toBeUndefined();
+    });
+
+    it('should return diagnostics for invalid grammar code', async () => {
+        const invalidCode = `
+            grammar HelloWorld
+            entry Model: persons+=Person*;
+        `;
+
+        const result = await validateLangiumCode(invalidCode);
+        expect(result).toBeDefined();
+        expect(result).toContain("Error: Could not resolve reference to AbstractRule named 'Person'. at line 3, column 35");
+    });
+});

packages/langium-ai-mcp/tests/mcp-server.test.ts

@@ -0,0 +1,32 @@
+{
+    "compilerOptions": {
+        "rootDir": "./src",
+        "outDir": "./dist",
+        "module": "nodenext",
+        "target": "esnext",
+        "types": [
+            "node"
+        ],
+        "sourceMap": true,
+        "declaration": true,
+        "declarationMap": true,
+        "noUncheckedIndexedAccess": true,
+        "exactOptionalPropertyTypes": true,
+        "strict": true,
+        "jsx": "react-jsx",
+        "verbatimModuleSyntax": true,
+        "isolatedModules": true,
+        "noUncheckedSideEffectImports": true,
+        "moduleDetection": "force",
+        "skipLibCheck": true,
+        "forceConsistentCasingInFileNames": true
+    },
+    "include": [
+        "src"
+    ],
+    "exclude": [
+        "node_modules",
+        "tests",
+        "dist"
+    ]
+}

packages/langium-ai-mcp/tsconfig.json

@@ -0,0 +1,14 @@
+{
+    "extends": "./tsconfig.json",
+    "compilerOptions": {
+        "types": ["vitest/globals", "node"]
+    },
+    "include": [
+        "src/**/*",
+        "tests/**/*"
+    ],
+    "exclude": [
+        "node_modules",
+        "dist"
+    ]
+}