diff --git a/src/api/endpoints/drive.js b/src/api/endpoints/drive.ts
similarity index 100%
rename from src/api/endpoints/drive.js
rename to src/api/endpoints/drive.ts
diff --git a/src/api/endpoints/i.js b/src/api/endpoints/i.ts
similarity index 100%
rename from src/api/endpoints/i.js
rename to src/api/endpoints/i.ts
diff --git a/src/api/endpoints/meta.js b/src/api/endpoints/meta.ts
similarity index 100%
rename from src/api/endpoints/meta.js
rename to src/api/endpoints/meta.ts
diff --git a/src/api/endpoints/posts.js b/src/api/endpoints/posts.js
deleted file mode 100644
index 42294a39c..000000000
--- a/src/api/endpoints/posts.js
+++ /dev/null
@@ -1,87 +0,0 @@
-'use strict';
-
-/**
- * Module dependencies
- */
-import Post from '../models/post';
-import serialize from '../serializers/post';
-
-/**
- * Lists all posts
- *
- * @param {any} params
- * @return {Promise<any>}
- */
-module.exports = (params) =>
-	new Promise(async (res, rej) => {
-		// Get 'include_replies' parameter
-		let includeReplies = params.include_replies;
-		if (includeReplies === true) {
-			includeReplies = true;
-		} else {
-			includeReplies = false;
-		}
-
-		// Get 'include_reposts' parameter
-		let includeReposts = params.include_reposts;
-		if (includeReposts === true) {
-			includeReposts = true;
-		} else {
-			includeReposts = false;
-		}
-
-		// Get 'limit' parameter
-		let limit = params.limit;
-		if (limit !== undefined && limit !== null) {
-			limit = parseInt(limit, 10);
-
-			// From 1 to 100
-			if (!(1 <= limit && limit <= 100)) {
-				return rej('invalid limit range');
-			}
-		} else {
-			limit = 10;
-		}
-
-		const since = params.since_id || null;
-		const max = params.max_id || null;
-
-		// Check if both of since_id and max_id is specified
-		if (since !== null && max !== null) {
-			return rej('cannot set since_id and max_id');
-		}
-
-		// Construct query
-		const sort = {
-			_id: -1
-		};
-		const query = {};
-		if (since !== null) {
-			sort._id = 1;
-			query._id = {
-				$gt: new mongo.ObjectID(since)
-			};
-		} else if (max !== null) {
-			query._id = {
-				$lt: new mongo.ObjectID(max)
-			};
-		}
-
-		if (!includeReplies) {
-			query.reply_to_id = null;
-		}
-
-		if (!includeReposts) {
-			query.repost_id = null;
-		}
-
-		// Issue query
-		const posts = await Post
-			.find(query, {
-				limit: limit,
-				sort: sort
-			});
-
-		// Serialize
-		res(await Promise.all(posts.map(async post => await serialize(post))));
-	});
diff --git a/src/api/endpoints/posts.ts b/src/api/endpoints/posts.ts
new file mode 100644
index 000000000..458f7d3de
--- /dev/null
+++ b/src/api/endpoints/posts.ts
@@ -0,0 +1,76 @@
+'use strict';
+
+/**
+ * Module dependencies
+ */
+import it from '../it';
+import Post from '../models/post';
+import serialize from '../serializers/post';
+
+/**
+ * Lists all posts
+ *
+ * @param {any} params
+ * @return {Promise<any>}
+ */
+module.exports = (params) =>
+	new Promise(async (res, rej) => {
+		// Get 'include_replies' parameter
+		const [includeReplies, includeRepliesErr] = it(params.include_replies).expect.boolean().default(true).qed();
+		if (includeRepliesErr) return rej('invalid include_replies param');
+
+		// Get 'include_reposts' parameter
+		const [includeReposts, includeRepostsErr] = it(params.include_reposts).expect.boolean().default(true).qed();
+		if (includeRepostsErr) return rej('invalid include_reposts param');
+
+		// Get 'limit' parameter
+		const [limit, limitErr] = it(params.limit).expect.number().range(1, 100).default(10).qed();
+		if (limitErr) return rej('invalid limit param');
+
+		// Get 'since_id' parameter
+		const [sinceId, sinceIdErr] = it(params.since_id).expect.id().qed();
+		if (sinceIdErr) return rej('invalid since_id param');
+
+		// Get 'max_id' parameter
+		const [maxId, maxIdErr] = it(params.max_id).expect.id().qed();
+		if (maxIdErr) return rej('invalid max_id param');
+
+		// Check if both of since_id and max_id is specified
+		if (sinceId !== null && maxId !== null) {
+			return rej('cannot set since_id and max_id');
+		}
+
+		// Construct query
+		const sort = {
+			_id: -1
+		};
+		const query = {} as any;
+		if (sinceId) {
+			sort._id = 1;
+			query._id = {
+				$gt: sinceId
+			};
+		} else if (maxId) {
+			query._id = {
+				$lt: maxId
+			};
+		}
+
+		if (!includeReplies) {
+			query.reply_to_id = null;
+		}
+
+		if (!includeReposts) {
+			query.repost_id = null;
+		}
+
+		// Issue query
+		const posts = await Post
+			.find(query, {
+				limit: limit,
+				sort: sort
+			});
+
+		// Serialize
+		res(await Promise.all(posts.map(async post => await serialize(post))));
+	});
diff --git a/src/api/endpoints/posts/favorites/create.ts b/src/api/endpoints/posts/favorites/create.ts
index 5be338593..45a347ebb 100644
--- a/src/api/endpoints/posts/favorites/create.ts
+++ b/src/api/endpoints/posts/favorites/create.ts
@@ -22,7 +22,7 @@ module.exports = (params, user) =>
 
 		// Get favoritee
 		const post = await Post.findOne({
-			_id: new mongo.ObjectID(postId)
+			_id: postId
 		});
 
 		if (post === null) {
diff --git a/src/api/endpoints/posts/favorites/delete.ts b/src/api/endpoints/posts/favorites/delete.ts
index 4dfd76158..df1121590 100644
--- a/src/api/endpoints/posts/favorites/delete.ts
+++ b/src/api/endpoints/posts/favorites/delete.ts
@@ -22,7 +22,7 @@ module.exports = (params, user) =>
 
 		// Get favoritee
 		const post = await Post.findOne({
-			_id: new mongo.ObjectID(postId)
+			_id: postId
 		});
 
 		if (post === null) {
diff --git a/src/api/endpoints/users.js b/src/api/endpoints/users.ts
similarity index 55%
rename from src/api/endpoints/users.js
rename to src/api/endpoints/users.ts
index 63e28caa4..74c4754fe 100644
--- a/src/api/endpoints/users.js
+++ b/src/api/endpoints/users.ts
@@ -3,6 +3,7 @@
 /**
  * Module dependencies
  */
+import it from '../it';
 import User from '../models/user';
 import serialize from '../serializers/user';
 
@@ -16,23 +17,19 @@ import serialize from '../serializers/user';
 module.exports = (params, me) =>
 	new Promise(async (res, rej) => {
 		// Get 'limit' parameter
-		let limit = params.limit;
-		if (limit !== undefined && limit !== null) {
-			limit = parseInt(limit, 10);
+		const [limit, limitErr] = it(params.limit).expect.number().range(1, 100).default(10).qed();
+		if (limitErr) return rej('invalid limit param');
 
-			// From 1 to 100
-			if (!(1 <= limit && limit <= 100)) {
-				return rej('invalid limit range');
-			}
-		} else {
-			limit = 10;
-		}
+		// Get 'since_id' parameter
+		const [sinceId, sinceIdErr] = it(params.since_id).expect.id().qed();
+		if (sinceIdErr) return rej('invalid since_id param');
 
-		const since = params.since_id || null;
-		const max = params.max_id || null;
+		// Get 'max_id' parameter
+		const [maxId, maxIdErr] = it(params.max_id).expect.id().qed();
+		if (maxIdErr) return rej('invalid max_id param');
 
 		// Check if both of since_id and max_id is specified
-		if (since !== null && max !== null) {
+		if (sinceId !== null && maxId !== null) {
 			return rej('cannot set since_id and max_id');
 		}
 
@@ -40,15 +37,15 @@ module.exports = (params, me) =>
 		const sort = {
 			_id: -1
 		};
-		const query = {};
-		if (since !== null) {
+		const query = {} as any;
+		if (sinceId) {
 			sort._id = 1;
 			query._id = {
-				$gt: new mongo.ObjectID(since)
+				$gt: sinceId
 			};
-		} else if (max !== null) {
+		} else if (maxId) {
 			query._id = {
-				$lt: new mongo.ObjectID(max)
+				$lt: maxId
 			};
 		}