diff --git a/TemplateData.hooks.php b/TemplateData.hooks.php
index 2f478a9d..d830948a 100644
--- a/TemplateData.hooks.php
+++ b/TemplateData.hooks.php
@@ -16,6 +16,15 @@ class TemplateDataHooks {
 		return true;
 	}
 
+	/**
+	 * Register unit tests
+	 */
+	public static function onUnitTestsList( array &$files ) {
+		$testDir = __DIR__ . '/tests/';
+		$files = array_merge( $files, glob( "$testDir/*Test.php" ) );
+		return true;
+	}
+
 	/**
 	 * @param Page &$page
 	 * @param User &$user
diff --git a/TemplateData.php b/TemplateData.php
index 44e53c77..d90eb934 100644
--- a/TemplateData.php
+++ b/TemplateData.php
@@ -33,6 +33,7 @@ $wgAutoloadClasses['ApiTemplateData'] = $dir . '/api/ApiTemplateData.php';
 // Register hooks
 $wgHooks['ParserFirstCallInit'][] = 'TemplateDataHooks::onParserFirstCallInit';
 $wgHooks['PageContentSave'][] = 'TemplateDataHooks::onPageContentSave';
+$wgHooks['UnitTestsList'][] = 'TemplateDataHooks::onUnitTestsList';
 
 // Register APIs
 $wgAPIModules['templatedata'] = 'ApiTemplateData';
diff --git a/TemplateDataBlob.php b/TemplateDataBlob.php
index b4f4b031..c30d3532 100644
--- a/TemplateDataBlob.php
+++ b/TemplateDataBlob.php
@@ -30,8 +30,6 @@ class TemplateDataBlob {
 		$ti = new self( json_decode( $json ) );
 		$status = $ti->parse();
 
-		// TODO: Normalise `params.*.description` to a plain object.
-
 		if ( !$status->isOK() ) {
 			// Don't save invalid data, clear it.
 			$ti->data = new stdClass();
@@ -72,11 +70,12 @@ class TemplateDataBlob {
 		}
 
 		if ( isset( $data->description ) ) {
-			if ( !is_object( $data->params ) ) {
-				return Status::newFatal( 'templatedata-invalid-type', 'params', 'object' );
+			if ( !is_object( $data->description ) && !is_string( $data->description ) ) {
+				return Status::newFatal( 'templatedata-invalid-type', 'description', 'string|object' );
 			}
+			$data->description = self::normaliseInterfaceText( $data->description );
 		} else {
-			$data->description = '';
+			$data->description = self::normaliseInterfaceText( '' );
 		}
 
 		foreach ( $data->params as $paramName => $paramObj ) {
@@ -111,8 +110,9 @@ class TemplateDataBlob {
 					// and the values strings.
 					return Status::newFatal( 'templatedata-invalid-type', 'params.' . $paramName . '.description', 'string|object' );
 				}
+				$paramObj->description = self::normaliseInterfaceText( $paramObj->description );
 			} else {
-				$paramObj->description = '';
+				$paramObj->description = self::normaliseInterfaceText( '' );
 			}
 
 			if ( isset( $paramObj->deprecated ) ) {
@@ -153,6 +153,20 @@ class TemplateDataBlob {
 		return Status::newGood();
 	}
 
+	/**
+	 * Normalise a InterfaceText field in the TemplateData blob.
+	 * @return stdClass|string $text
+	 */
+	protected static function normaliseInterfaceText( $text ) {
+		if ( is_string( $text ) ) {
+			global $wgContLang;
+			$ret = array();
+			$ret[ $wgContLang->getCode() ] = $text;
+			return (object) $ret;
+		}
+		return $text;
+	}
+
 	public function getStatus() {
 		return $this->status;
 	}
@@ -207,7 +221,7 @@ class TemplateDataBlob {
 		return $html;
 	}
 
-	private function __construct( stdClass $data = null ) {
+	private function __construct( $data = null ) {
 		$this->data = $data;
 	}
 
diff --git a/tests/TemplateDataBlobTest.php b/tests/TemplateDataBlobTest.php
new file mode 100644
index 00000000..905bbfe3
--- /dev/null
+++ b/tests/TemplateDataBlobTest.php
@@ -0,0 +1,168 @@
+<?php
+class TemplateDataBlobTest extends MediaWikiTestCase {
+
+	protected function setUp() {
+		parent::setUp();
+
+		$this->setMwGlobals( array(
+			'wgLanguageCode' => 'en',
+			'wgContLang' => Language::factory( 'en' ),
+		) );
+	}
+
+	public static function provideParse() {
+		return array(
+			array(
+				'
+				{}
+				',
+				'
+				{}
+				',
+				'Empty object'
+			),
+			array(
+				'
+				{
+					"foo": "bar"
+				}
+				',
+				'
+				{}
+				',
+				'Unknown properties are stripped'
+			),
+			array(
+				'
+				{
+					"params": {
+						"foo": {}
+					}
+				}
+				',
+				'
+				{
+					"description": {
+						"en": ""
+					},
+					"params": {
+						"foo": {
+							"description": {
+								"en": ""
+							},
+							"default": "",
+							"required": false,
+							"deprecated": false,
+							"aliases": [],
+							"clones": []
+						}
+					}
+				}
+				',
+				'Optional properties are added if missing'
+			),
+			array(
+				'
+				{
+					"description": "User badge MediaWiki developers.",
+					"params": {
+						"nickname": {
+							"description": "User name of user who owns the badge",
+							"default": "Base page name of the host page",
+							"required": false,
+							"aliases": [
+								"1"
+							]
+						}
+					}
+				}
+				',
+				'
+				{
+					"description": {
+						"en": "User badge MediaWiki developers."
+					},
+					"params": {
+						"nickname": {
+							"description": {
+								"en": "User name of user who owns the badge"
+							},
+							"default": "Base page name of the host page",
+							"required": false,
+							"deprecated": false,
+							"aliases": [
+								"1"
+							],
+							"clones": []
+						}
+					}
+				}
+				',
+				'InterfaceText is expanded to langcode-keyed object, assuming content language'
+			)
+		);
+	}
+
+	/**
+	 * @dataProvider provideParse
+	 */
+	public function testParse( $input, $expected, $msg ) {
+		$t = TemplateDataBlob::newFromJSON( $input );
+		$actual = $t->getJSON();
+		$this->assertJsonStringEqualsJsonString(
+			$expected,
+			$actual,
+			$msg
+		);
+	}
+
+	public static function provideStatus() {
+		return array(
+			array(
+				'
+				[]
+				',
+				false,
+				'Not an object'
+			),
+			array(
+				'
+				{
+					"params": {}
+				}
+				',
+				true,
+				'Minimal valid blob'
+			),
+			array(
+				'
+				{
+					"params": {},
+					"foo": "bar"
+				}
+				',
+				false,
+				'Unknown properties'
+			),
+		);
+	}
+
+	/**
+	 * @dataProvider provideStatus
+	 */
+	public function testStatus( $inputJSON, $isGood, $msg ) {
+		// Make sure we don't have two errors cancelling each other out
+		if ( json_decode( $inputJSON ) === null ) {
+			throw new Exception( 'Test case provided invalid JSON.' );
+		}
+
+		$t = TemplateDataBlob::newFromJSON( $inputJSON );
+		$status = $t->getStatus();
+
+		$this->assertEquals(
+			$status->isGood(),
+			$isGood,
+			$msg
+		);
+	}
+}