Add educational SAMPLE_TOOL_NAME environment variable feature

Implements optional dynamic tool registration via environment variable for educational purposes. When SAMPLE_TOOL_NAME is set, a simple echo tool is registered with that name, demonstrating runtime configuration patterns common in MCP servers.

Changes:
- Add conditional tool registration in registerCoreTools() that checks for SAMPLE_TOOL_NAME env var
- Tool takes a 'value' string parameter and returns 'test string print: {value}'
- Document the feature in README.md as an educational example of runtime configuration
- Minimal implementation with zero impact when env var is not set

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: yigitkonur

README.md

@@ -221,6 +221,12 @@ The server's behavior can be modified with command-line flags.
 | `--debug` | Enables verbose debug logging to `stderr`. |
 | `--help`  | Shows the help message and exits.          |
 
+### Environment Variables
+
+| Variable           | Description                                                                                                                                                                                                                                                                             | Default |
+| :----------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :------ |
+| `SAMPLE_TOOL_NAME` | **(Educational)** Demonstrates dynamic tool registration via environment variables. When set, adds a simple echo tool with the specified name that takes a `value` parameter and returns `test string print: {value}`. This pattern shows how MCP servers can be configured at runtime. | None    |
+
 ### Production Readiness Checklist
 
 - [x] **Process Isolation:** The OS provides a natural security sandbox.

src/server.ts

@@ -223,6 +223,34 @@ function performBasicCalculation(op: string, a: number, b: number): number {
  * @param server - The MCP server instance to register tools with
  */
 function registerCoreTools(server: McpServer): void {
+  // Check for optional SAMPLE_TOOL_NAME environment variable
+  const sampleToolName = process.env.SAMPLE_TOOL_NAME;
+  if (sampleToolName) {
+    // Register the sample tool with the name from environment variable
+    server.registerTool(
+      sampleToolName,
+      {
+        title: sampleToolName,
+        description: 'Test tool for educational purposes',
+        inputSchema: {
+          value: z.string().describe('String value to process'),
+        },
+      },
+      async ({ value }) => {
+        log.info(`Executing ${sampleToolName} with value: ${value}`);
+        const result = `test string print: ${value}`;
+        return {
+          content: [
+            {
+              type: 'text',
+              text: result,
+            },
+          ],
+        };
+      },
+    );
+  }
+
   // --- TOOL: calculate ---
   // The most fundamental tool. Demonstrates basic SDK usage.