diff --git a/app/templating/index.js b/app/templating/index.js
index 68c6fc000..3b7e35297 100644
--- a/app/templating/index.js
+++ b/app/templating/index.js
@@ -1,7 +1,23 @@
+// @flow
 import nunjucks from 'nunjucks';
 import * as extensions from './extensions';
 import BaseExtension from './base-extension';
 
+export class RenderError extends Error {
+  message: string;
+  path: string | null;
+  location: {line: number, column: number};
+  type: string;
+  reason: string;
+}
+
+export type NunjucksTag = {
+  name: string,
+  displayName: string,
+  description: string,
+  args: Array<Object>
+};
+
 // Some constants
 export const RENDER_ALL = 'all';
 export const RENDER_VARS = 'variables';
@@ -20,7 +36,7 @@ let nunjucksAll = null;
  * @param {Object} [config.path] - Path to include in the error message
  * @param {Object} [config.renderMode] - Only render variables (not tags)
  */
-export function render (text, config = {}) {
+export function render (text: string, config: Object = {}): Promise<string> {
   const context = config.context || {};
   const path = config.path || null;
   const renderMode = config.renderMode || RENDER_ALL;
@@ -43,7 +59,7 @@ export function render (text, config = {}) {
           ? 'undefined'
           : 'error';
 
-        const newError = new Error(sanitizedMsg);
+        const newError = new RenderError(sanitizedMsg);
         newError.path = path || null;
         newError.message = sanitizedMsg;
         newError.location = {line, column};
@@ -60,7 +76,7 @@ export function render (text, config = {}) {
 /**
  * Reload Nunjucks environments. Useful for if plugins change.
  */
-export function reload () {
+export function reload (): void {
   nunjucksAll = null;
   nunjucksVariablesOnly = null;
   nunjucksTagsOnly = null;
diff --git a/flow-typed/nunjucks.js b/flow-typed/nunjucks.js
new file mode 100644
index 000000000..fe08fd8b3
--- /dev/null
+++ b/flow-typed/nunjucks.js
@@ -0,0 +1,25 @@
+declare class Nunjucks<T> {
+  extensions: {[string]: T},
+  addExtension: (name: string, ext: T) => void,
+  addFilter: (name: string, ext: Function) => void,
+  renderString: (text: string, context: Object, callback: Function) => void
+}
+
+declare type Config = {
+  autoescape: boolean,
+  throwOnUndefined: boolean,
+  tags: {
+    blockStart: string,
+    blockEnd: string,
+    variableStart: string,
+    variableEnd: string,
+    commentStart: string,
+    commentEnd: string
+  }
+};
+
+declare module 'nunjucks' {
+  declare module.exports: {
+    configure: <T>(config: Config) => Nunjucks<T>
+  }
+}