diff --git a/src/main/scala/api/ApiError.scala b/src/main/scala/api/ApiError.scala
new file mode 100644
index 0000000..d0470dc
--- /dev/null
+++ b/src/main/scala/api/ApiError.scala
@@ -0,0 +1,5 @@
+package api
+
+case class ApiError(
+  message: String,
+  documentation_url: Option[String] = None)
diff --git a/src/main/scala/app/AccountController.scala b/src/main/scala/app/AccountController.scala
index 53f353a..b2650fc 100644
--- a/src/main/scala/app/AccountController.scala
+++ b/src/main/scala/app/AccountController.scala
@@ -167,7 +167,7 @@
   get("/api/v3/user") {
     context.loginAccount.map { account =>
       JsonFormat(ApiUser(account))
-    } getOrElse NotFound
+    } getOrElse Unauthorized
   }
 
 
diff --git a/src/main/scala/app/ControllerBase.scala b/src/main/scala/app/ControllerBase.scala
index ed9691b..a8b31fc 100644
--- a/src/main/scala/app/ControllerBase.scala
+++ b/src/main/scala/app/ControllerBase.scala
@@ -51,6 +51,9 @@
       // Git repository
       chain.doFilter(request, response)
     } else {
+      if(path.startsWith("/api/v3/")){
+        httpRequest.setAttribute(Keys.Request.APIv3, true)
+      }
       // Scalatra actions
       super.doFilter(request, response, chain)
     }
@@ -103,6 +106,9 @@
   protected def NotFound() =
     if(request.hasAttribute(Keys.Request.Ajax)){
       org.scalatra.NotFound()
+    } else if(request.hasAttribute(Keys.Request.APIv3)){
+      contentType = formats("json")
+      org.scalatra.NotFound(api.ApiError("Not Found"))
     } else {
       org.scalatra.NotFound(html.error("Not Found"))
     }
@@ -110,6 +116,9 @@
   protected def Unauthorized()(implicit context: app.Context) =
     if(request.hasAttribute(Keys.Request.Ajax)){
       org.scalatra.Unauthorized()
+    } else if(request.hasAttribute(Keys.Request.APIv3)){
+      contentType = formats("json")
+      org.scalatra.Unauthorized(api.ApiError("Requires authentication"))
     } else {
       if(context.loginAccount.isDefined){
         org.scalatra.Unauthorized(redirect("/"))
diff --git a/src/main/scala/util/Keys.scala b/src/main/scala/util/Keys.scala
index a934058..b6b6c79 100644
--- a/src/main/scala/util/Keys.scala
+++ b/src/main/scala/util/Keys.scala
@@ -72,6 +72,11 @@
     val Ajax = "AJAX"
 
     /**
+     * Request key for the /api/v3 request flag.
+     */
+    val APIv3 = "APIv3"
+
+    /**
      * Request key for the username which is used during Git repository access.
      */
     val UserName = "USER_NAME"