diff --git a/public/openapi/components/schemas/PostsObject.yaml b/public/openapi/components/schemas/PostsObject.yaml
index ed546b052ad0..5c68196b2cbf 100644
--- a/public/openapi/components/schemas/PostsObject.yaml
+++ b/public/openapi/components/schemas/PostsObject.yaml
@@ -1,4 +1,5 @@
 PostsObject:
+  description: One of the objects in the array returned from `Posts.getPostSummaryByPids`
   type: array
   items:
     type: object
diff --git a/public/openapi/write.yaml b/public/openapi/write.yaml
index ccb94eccfca6..623c6a136fed 100644
--- a/public/openapi/write.yaml
+++ b/public/openapi/write.yaml
@@ -456,6 +456,84 @@ paths:
                   response:
                     type: object
                     properties: {}
+  /topics:
+    post:
+      tags:
+        - topics
+      summary: Create a new topic
+      description: This operation creates a new topic with a post. Topic creation without a post is not allowed via the Write API as it is an internal-only method.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                cid:
+                  type: number
+                title:
+                  type: string
+                content:
+                  type: string
+                tags:
+                  type: array
+                  items:
+                    type: string
+              required:
+                - cid
+                - title
+                - content
+            example:
+              cid: 1
+              title: Test topic
+              content: This is the test topic's content
+      responses:
+        '200':
+          description: topic successfully created
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  status:
+                    $ref: '#/components/schemas/Status'
+                  response:
+                    $ref: components/schemas/TopicObject.yaml#/TopicObject
+  /topics/{tid}:
+    post:
+      tags:
+        - topics
+      summary: Reply to a topic
+      description: This operation creates a new reply to an existing topic.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                content:
+                  type: string
+                timestamp:
+                  type: number
+                toPid:
+                  type: number
+              required:
+                - content
+            example:
+              content: This is a test reply
+      responses:
+        '200':
+          description: post successfully created
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  status:
+                    $ref: '#/components/schemas/Status'
+                  response:
+                    $ref: components/schemas/PostsObject.yaml#/PostsObject
 components:
   schemas:
     Status:
diff --git a/src/controllers/helpers.js b/src/controllers/helpers.js
index 08419ee8970d..76dc5f6fa4cf 100644
--- a/src/controllers/helpers.js
+++ b/src/controllers/helpers.js
@@ -3,6 +3,7 @@
 const nconf = require('nconf');
 const validator = require('validator');
 const querystring = require('querystring');
+const url = require('url');
 const _ = require('lodash');
 
 const user = require('../user');
@@ -413,4 +414,28 @@ helpers.generateError = (statusCode, message) => {
 	return payload;
 };
 
+helpers.buildReqObject = (req) => {
+	var headers = req.headers;
+	var encrypted = !!req.connection.encrypted;
+	var host = headers.host;
+	var referer = headers.referer || '';
+	if (!host) {
+		host = url.parse(referer).host || '';
+	}
+
+	return {
+		uid: req.uid,
+		params: req.params,
+		method: req.method,
+		body: req.body,
+		ip: req.ip,
+		host: host,
+		protocol: encrypted ? 'https' : 'http',
+		secure: encrypted,
+		url: referer,
+		path: referer.substr(referer.indexOf(host) + host.length),
+		headers: headers,
+	};
+};
+
 require('../promisify')(helpers);
diff --git a/src/controllers/write/index.js b/src/controllers/write/index.js
index be642c280768..693c49d2327a 100644
--- a/src/controllers/write/index.js
+++ b/src/controllers/write/index.js
@@ -3,4 +3,6 @@
 const Write = module.exports;
 
 Write.users = require('./users');
+Write.groups = require('./groups');
 Write.categories = require('./categories');
+Write.topics = require('./topics');
diff --git a/src/middleware/assert.js b/src/middleware/assert.js
index 3b80c166a940..72b971eedefb 100644
--- a/src/middleware/assert.js
+++ b/src/middleware/assert.js
@@ -6,13 +6,23 @@
  */
 
 const groups = require('../groups');
+const topics = require('../topics');
+
+const helpers = require('../controllers/helpers');
 
 module.exports = function (middleware) {
 	middleware.assertGroup = async (req, res, next) => {
 		const name = await groups.getGroupNameByGroupSlug(req.params.slug);
-		const exists = await groups.exists(name);
-		if (!exists) {
-			throw new Error('[[error:no-group]]');
+		if (!name || await groups.exists(name)) {
+			return helpers.formatApiResponse(404, res, new Error('[[error:no-group]]'));
+		}
+
+		next();
+	};
+
+	middleware.assertTopic = async (req, res, next) => {
+		if (!await topics.exists(req.params.tid)) {
+			return helpers.formatApiResponse(404, res, new Error('[[error:no-topic]]'));
 		}
 
 		next();
diff --git a/src/routes/write/index.js b/src/routes/write/index.js
index 62de9501bee4..46cc85ca40a9 100644
--- a/src/routes/write/index.js
+++ b/src/routes/write/index.js
@@ -21,11 +21,11 @@ Write.reload = (params) => {
 	});
 
 	router.use('/api/v1/users', require('./users')());
-	// router.use('/groups', require('./groups')(coreMiddleware));
-	// router.use('/posts', require('./posts')(coreMiddleware));
-	// router.use('/topics', require('./topics')(coreMiddleware));
+	router.use('/api/v1/groups', require('./groups')());
 	router.use('/api/v1/categories', require('./categories')());
-	// router.use('/util', require('./util')(coreMiddleware));
+	router.use('/api/v1/topics', require('./topics')());
+	// router.use('/api/v1/posts', require('./posts')());
+	// router.use('/api/v1/util', require('./util')());
 
 	router.get('/api/v1/ping', function (req, res) {
 		helpers.formatApiResponse(200, res, {
diff --git a/src/socket.io/posts.js b/src/socket.io/posts.js
index 83d0dfe86d33..1096f59239a2 100644
--- a/src/socket.io/posts.js
+++ b/src/socket.io/posts.js
@@ -13,6 +13,7 @@ const utils = require('../utils');
 
 const apiController = require('../controllers/api');
 
+const sockets = require('.');
 const SocketPosts = module.exports;
 
 require('./posts/edit')(SocketPosts);
@@ -23,6 +24,8 @@ require('./posts/tools')(SocketPosts);
 require('./posts/diffs')(SocketPosts);
 
 SocketPosts.reply = async function (socket, data) {
+	sockets.warnDeprecated(socket, 'POST /api/v1/topics/:tid');
+
 	if (!data || !data.tid || (meta.config.minimumPostLength !== 0 && !data.content)) {
 		throw new Error('[[error:invalid-data]]');
 	}
diff --git a/src/socket.io/topics.js b/src/socket.io/topics.js
index 6669dc8a8909..56e33266b78f 100644
--- a/src/socket.io/topics.js
+++ b/src/socket.io/topics.js
@@ -6,6 +6,7 @@ const user = require('../user');
 const meta = require('../meta');
 const apiController = require('../controllers/api');
 const privileges = require('../privileges');
+const sockets = require('.');
 const socketHelpers = require('./helpers');
 
 const SocketTopics = module.exports;
@@ -18,6 +19,8 @@ require('./topics/tags')(SocketTopics);
 require('./topics/merge')(SocketTopics);
 
 SocketTopics.post = async function (socket, data) {
+	sockets.warnDeprecated(socket, 'POST /api/v1/topics');
+
 	if (!data) {
 		throw new Error('[[error:invalid-data]]');
 	}