diff --git a/packages/plugin-ext/src/hosted/node/scanners/file-plugin-uri-factory.ts b/packages/plugin-ext/src/hosted/node/scanners/file-plugin-uri-factory.ts
index b262bf7c6e092..23ef9748c27ec 100644
--- a/packages/plugin-ext/src/hosted/node/scanners/file-plugin-uri-factory.ts
+++ b/packages/plugin-ext/src/hosted/node/scanners/file-plugin-uri-factory.ts
@@ -1,4 +1,3 @@
-
 /********************************************************************************
  * Copyright (C) 2020 Red Hat, Inc.
  *
@@ -21,7 +20,10 @@ import URI from '@theia/core/lib/common/uri';
 import { FileUri } from '@theia/core/lib/node/file-uri';
 import { PluginPackage } from '../../../common';
 import { PluginUriFactory } from './plugin-uri-factory';
-
+/**
+ * The default implementation of PluginUriFactory simply returns a File URI from the concatenated
+ * package path and relative path.
+ */
 @injectable()
 export class FilePluginUriFactory implements PluginUriFactory {
     createUri(pkg: PluginPackage, pkgRelativePath?: string): URI {
diff --git a/packages/plugin-ext/src/hosted/node/scanners/plugin-uri-factory.ts b/packages/plugin-ext/src/hosted/node/scanners/plugin-uri-factory.ts
index 4223b2f23757d..9e41f42eb44af 100644
--- a/packages/plugin-ext/src/hosted/node/scanners/plugin-uri-factory.ts
+++ b/packages/plugin-ext/src/hosted/node/scanners/plugin-uri-factory.ts
@@ -1,4 +1,3 @@
-
 /********************************************************************************
  * Copyright (C) 2020 Red Hat, Inc.
  *
@@ -19,7 +18,16 @@ import URI from '@theia/core/lib/common/uri';
 import { PluginPackage } from '../../../common';
 
 export const PluginUriFactory = Symbol('PluginUriFactory');
-
+/**
+ * Creates URIs for resources used in plugin contributions. Projects where plugin host is not located on the back-end
+ * machine and therefor resources cannot be loaded from the local file system in the back end can override the factory.
+ */
 export interface PluginUriFactory {
+    /**
+     * Returns a URI that allows a file to be loaded given a plugin package and a path relative to the plugin's package path
+     *
+     * @param pkg the package this the file is contained in
+     * @param pkgRelativePath the path of the file relative to the package path, e.g. 'resources/snippets.json'
+     */
     createUri(pkg: PluginPackage, pkgRelativePath?: string): URI;
 }