feat: Add support for running the server in ReadOnly mode (#50)

* feat: add conditional registration of modification tools based on read-only mode

* docs: add instructions for running MCP Server in ReadOnly mode

* fix lint

---------

Co-authored-by: Jiacheng Xu <xjcmaxwellcjx@gmail.com>

Author: mstiri

README.md

@@ -129,6 +129,22 @@ This disables TLS certificate validation for Node.js when connecting to Argo CD
 
 > **Warning**: Disabling SSL verification reduces security. Use this setting only in development environments or when you understand the security implications.
 
+
+### Read Only Mode
+
+If you want to run the MCP Server in a ReadOnly mode to avoid resource or application modification, you should set the environment variable:
+```
+"MCP_READ_ONLY": "true"
+```
+This will disable the following tools:
+- `create_application`
+- `update_application`
+- `delete_application`
+- `sync_application`
+- `run_resource_action`
+
+By default, all the tools will be available.
+
 ## Available Tools
 
 The server provides the following ArgoCD management tools:

src/server/server.ts

@@ -25,6 +25,12 @@ export class Server extends McpServer {
     });
     this.argocdClient = new ArgoCDClient(serverInfo.argocdBaseUrl, serverInfo.argocdApiToken);
 
+    const isReadOnly =
+      String(process.env.MCP_READ_ONLY ?? '')
+        .trim()
+        .toLowerCase() === 'true';
+
+    // Always register read/query tools
     this.addJsonOutputTool(
       'list_applications',
       'list_applications returns list of applications',
@@ -45,35 +51,6 @@ export class Server extends McpServer {
       { applicationName: z.string() },
       async ({ applicationName }) => await this.argocdClient.getApplication(applicationName)
     );
-    this.addJsonOutputTool(
-      'create_application',
-      'create_application creates application',
-      { application: ApplicationSchema },
-      async ({ application }) =>
-        await this.argocdClient.createApplication(application as V1alpha1Application)
-    );
-    this.addJsonOutputTool(
-      'update_application',
-      'update_application updates application',
-      { applicationName: z.string(), application: ApplicationSchema },
-      async ({ applicationName, application }) =>
-        await this.argocdClient.updateApplication(
-          applicationName,
-          application as V1alpha1Application
-        )
-    );
-    this.addJsonOutputTool(
-      'delete_application',
-      'delete_application deletes application',
-      { applicationName: z.string() },
-      async ({ applicationName }) => await this.argocdClient.deleteApplication(applicationName)
-    );
-    this.addJsonOutputTool(
-      'sync_application',
-      'sync_application syncs application',
-      { applicationName: z.string() },
-      async ({ applicationName }) => await this.argocdClient.syncApplication(applicationName)
-    );
     this.addJsonOutputTool(
       'get_application_resource_tree',
       'get_application_resource_tree returns resource tree for application by application name',
@@ -176,23 +153,56 @@ export class Server extends McpServer {
           resourceRef as V1alpha1ResourceResult
         )
     );
-    this.addJsonOutputTool(
-      'run_resource_action',
-      'run_resource_action runs an action on a resource',
-      {
-        applicationName: z.string(),
-        applicationNamespace: ApplicationNamespaceSchema,
-        resourceRef: ResourceRefSchema,
-        action: z.string()
-      },
-      async ({ applicationName, applicationNamespace, resourceRef, action }) =>
-        await this.argocdClient.runResourceAction(
-          applicationName,
-          applicationNamespace,
-          resourceRef as V1alpha1ResourceResult,
-          action
-        )
-    );
+
+    // Only register modification tools if not in read-only mode
+    if (!isReadOnly) {
+      this.addJsonOutputTool(
+        'create_application',
+        'create_application creates application',
+        { application: ApplicationSchema },
+        async ({ application }) =>
+          await this.argocdClient.createApplication(application as V1alpha1Application)
+      );
+      this.addJsonOutputTool(
+        'update_application',
+        'update_application updates application',
+        { applicationName: z.string(), application: ApplicationSchema },
+        async ({ applicationName, application }) =>
+          await this.argocdClient.updateApplication(
+            applicationName,
+            application as V1alpha1Application
+          )
+      );
+      this.addJsonOutputTool(
+        'delete_application',
+        'delete_application deletes application',
+        { applicationName: z.string() },
+        async ({ applicationName }) => await this.argocdClient.deleteApplication(applicationName)
+      );
+      this.addJsonOutputTool(
+        'sync_application',
+        'sync_application syncs application',
+        { applicationName: z.string() },
+        async ({ applicationName }) => await this.argocdClient.syncApplication(applicationName)
+      );
+      this.addJsonOutputTool(
+        'run_resource_action',
+        'run_resource_action runs an action on a resource',
+        {
+          applicationName: z.string(),
+          applicationNamespace: ApplicationNamespaceSchema,
+          resourceRef: ResourceRefSchema,
+          action: z.string()
+        },
+        async ({ applicationName, applicationNamespace, resourceRef, action }) =>
+          await this.argocdClient.runResourceAction(
+            applicationName,
+            applicationNamespace,
+            resourceRef as V1alpha1ResourceResult,
+            action
+          )
+      );
+    }
   }
 
   private addJsonOutputTool<Args extends ZodRawShape, T>(