diff --git a/denops/@ddc-sources/stamp.ts b/denops/@ddc-sources/stamp.ts
index 388e8f1..ae74017 100644
--- a/denops/@ddc-sources/stamp.ts
+++ b/denops/@ddc-sources/stamp.ts
@@ -1,21 +1,23 @@
 import {
+  assert,
   ddcVim,
   ddcVimSource,
   Denops,
-  ensureString,
+  ensure,
+  is,
   traq,
   vars,
 } from "../traqvim/deps.ts";
-
 import { getStamps } from "../traqvim/model.ts";
 import { api } from "../traqvim/api.ts";
+import { isDdcItem } from "../traqvim/type_check.ts";
 
 type Params = Record<never, never>;
 
 export class Source extends ddcVim.BaseSource<Params> {
   async onInit(args: ddcVimSource.OnInitArguments<Params>): Promise<void> {
     const path = await vars.globals.get(args.denops, "traqvim#token_file_path");
-    ensureString(path);
+    assert(path, is.String);
     api.tokenFilePath = path;
     return Promise.resolve();
   }
@@ -25,9 +27,9 @@ export class Source extends ddcVim.BaseSource<Params> {
     return stamps
       .filter((stamp) => stamp.name)
       .map((stamp) => {
-        return {
+        return ensure({
           word: ":" + stamp.name + ":",
-        } as ddcVim.Item;
+        }, isDdcItem);
       });
   }
 
diff --git a/denops/@ddu-columns/channel.ts b/denops/@ddu-columns/channel.ts
index 90b2859..0cdc621 100644
--- a/denops/@ddu-columns/channel.ts
+++ b/denops/@ddu-columns/channel.ts
@@ -1,4 +1,4 @@
-import { dduVim, dduVimColumn, fn } from "../traqvim/deps.ts";
+import { dduVim, dduVimColumn, ensure, fn, is } from "../traqvim/deps.ts";
 
 export type Params = {
   collapsedParentIcon: string;
@@ -36,7 +36,7 @@ export class Column extends dduVim.BaseColumn<Params> {
     const text =
       " ".repeat(args.columnParams.indentationWidth * args.item.__level) +
       icon + " " + args.item.word;
-    const width = await fn.strwidth(args.denops, text) as number;
+    const width = ensure(await fn.strwidth(args.denops, text), is.Number);
     const padding = " ".repeat(args.endCol - args.startCol - width);
     return Promise.resolve({
       text: text + padding,
diff --git a/denops/@ddu-kinds/channel.ts b/denops/@ddu-kinds/channel.ts
index 631dd04..eff511f 100644
--- a/denops/@ddu-kinds/channel.ts
+++ b/denops/@ddu-kinds/channel.ts
@@ -1,8 +1,10 @@
 import {
+  assert,
   dduVim,
   Denops,
-  ensureArray,
-  ensureNumber,
+  ensure,
+  is,
+  Predicate,
   vars,
 } from "../traqvim/deps.ts";
 import { channelMessageOptions, channelTimeline } from "../traqvim/model.ts";
@@ -10,16 +12,25 @@ import { actionOpenChannel } from "../traqvim/action.ts";
 import { Message } from "../traqvim/type.d.ts";
 
 // TODO: unkownutilのアプデしたらtype.d.tsのChannelとかに変更する
+// ChannelとUnreadChannelをUnion型にできなかったので、kindごと分ける
 export interface ActionData {
   id: string;
 }
 
+export const isActionData: Predicate<ActionData> = is.ObjectOf({
+  id: is.String,
+});
+
 type Params = Record<never, never>;
 
 type OpenParams = {
   command: string;
 };
 
+const isOpenParams: Predicate<OpenParams> = is.ObjectOf({
+  command: is.String,
+});
+
 export class Kind extends dduVim.BaseKind<Params> {
   actions: dduVim.Actions<Params> = {
     open: async (args: {
@@ -31,15 +42,14 @@ export class Kind extends dduVim.BaseKind<Params> {
         if (!item.action) {
           continue;
         }
-        // TODO: unkownutilのアプデしたらasをensureに変更
-        const action = item.action as ActionData;
+        const action = ensure(item.action, isActionData);
         const channelPath: string = item.word;
         const channelID: string = action.id;
         const limit = await vars.globals.get(
           args.denops,
           "traqvim#fetch_limit",
         );
-        ensureNumber(limit);
+        assert(limit, is.Number);
         const timelineOption: channelMessageOptions = {
           id: channelID,
           channelPath: channelPath,
@@ -47,7 +57,7 @@ export class Kind extends dduVim.BaseKind<Params> {
           until: new Date().toISOString(),
           order: "desc",
         };
-        const params = args.actionParams as OpenParams;
+        const params = ensure(args.actionParams, isOpenParams);
         if (params.command) {
           await args.denops.cmd(params.command);
         }
@@ -65,7 +75,7 @@ export class Kind extends dduVim.BaseKind<Params> {
       item: dduVim.DduItem;
     },
   ): Promise<dduVim.Previewer | undefined> {
-    const action = args.item.action as ActionData;
+    const action = ensure(args.item.action, isActionData);
     if (!action) {
       return undefined;
     }
@@ -80,7 +90,7 @@ export class Kind extends dduVim.BaseKind<Params> {
           message,
           args.previewContext.width,
         );
-        ensureArray<string>(ret);
+        assert(ret, is.ArrayOf(is.String));
         return ret;
       }),
     );
diff --git a/denops/@ddu-sources/channel.ts b/denops/@ddu-sources/channel.ts
index 805f43a..6e39ef5 100644
--- a/denops/@ddu-sources/channel.ts
+++ b/denops/@ddu-sources/channel.ts
@@ -1,9 +1,10 @@
 import {
+  assert,
   dduVim,
   dduVimSource,
   Denops,
-  ensureString,
   helper,
+  is,
   vars,
 } from "../traqvim/deps.ts";
 import { ActionData } from "../@ddu-kinds/channel.ts";
@@ -17,7 +18,7 @@ export class Source extends dduVim.BaseSource<Params> {
   kind = "channel";
   async onInit(args: dduVimSource.OnInitArguments<Params>): Promise<void> {
     const path = await vars.globals.get(args.denops, "traqvim#token_file_path");
-    ensureString(path);
+    assert(path, is.String);
     api.tokenFilePath = path;
     return Promise.resolve();
   }
diff --git a/denops/@ddu-sources/channel_rec.ts b/denops/@ddu-sources/channel_rec.ts
index ba71a01..b46a560 100644
--- a/denops/@ddu-sources/channel_rec.ts
+++ b/denops/@ddu-sources/channel_rec.ts
@@ -1,8 +1,9 @@
 import {
+  assert,
   dduVim,
   dduVimSource,
   Denops,
-  ensureString,
+  is,
   vars,
 } from "../traqvim/deps.ts";
 import { ActionData } from "../@ddu-kinds/channel.ts";
@@ -18,7 +19,7 @@ export class Source extends dduVim.BaseSource<Params> {
   kind = "channel";
   async onInit(args: dduVimSource.OnInitArguments<Params>): Promise<void> {
     const path = await vars.globals.get(args.denops, "traqvim#token_file_path");
-    ensureString(path);
+    assert(path, is.String);
     api.tokenFilePath = path;
     return Promise.resolve();
   }
diff --git a/denops/traqvim/action.ts b/denops/traqvim/action.ts
index b37da9b..1aee84f 100644
--- a/denops/traqvim/action.ts
+++ b/denops/traqvim/action.ts
@@ -1,4 +1,4 @@
-import { bufname, Denops, ensureArray, fn, helper, vars } from "./deps.ts";
+import { assert, bufname, Denops, fn, helper, is, vars } from "./deps.ts";
 import { ChannelBuffer, Message } from "./type.d.ts";
 import {
   activity,
@@ -9,6 +9,7 @@ import {
   editMessage,
   removePin,
 } from "./model.ts";
+import { isMessage } from "./type_check.ts";
 
 export const actionOpenChannel = async (
   denops: Denops,
@@ -56,7 +57,7 @@ export const actionForwardChannelMessage = async (
 ): Promise<void> => {
   // 既存メッセージの取得
   const timeline = await vars.buffers.get(denops, "channelTimeline");
-  ensureArray<Message>(timeline);
+  assert(timeline, is.ArrayOf(isMessage));
   // 追記したものをセット
   await vars.buffers.set(
     denops,
@@ -79,7 +80,7 @@ export const actionBackChannelMessage = async (
 ): Promise<void> => {
   // 既存メッセージの取得
   const timeline = await vars.buffers.get(denops, "channelTimeline");
-  ensureArray<Message>(timeline);
+  assert(timeline, is.ArrayOf(isMessage));
   // 追記したものをセット
   await vars.buffers.set(
     denops,
@@ -103,7 +104,7 @@ export const actionDeleteMessage = async (
   }
   // 既存メッセージの取得
   const timeline = await vars.buffers.get(denops, "channelTimeline");
-  ensureArray<Message>(timeline);
+  assert(timeline, is.ArrayOf(isMessage));
   // 削除したものをセット
   await vars.buffers.set(
     denops,
@@ -128,7 +129,7 @@ export const actionEditMessage = async (
   // 既存メッセージの取得
   // const timeline = await vars.buffers.get(denops, "channelTimeline");
   const timeline = await fn.getbufvar(denops, bufNum, "channelTimeline");
-  ensureArray<Message>(timeline);
+  assert(timeline, is.ArrayOf(isMessage));
   const editedTimeline = timeline.map((m) => {
     if (m.id === message.id) {
       return {
@@ -209,7 +210,7 @@ export const actionCreatePin = async (
   }
   // 既存メッセージの取得
   const timeline = await vars.buffers.get(denops, "channelTimeline");
-  ensureArray<Message>(timeline);
+  assert(timeline, is.ArrayOf(isMessage));
   message.pinned = true;
   // ピン留めしたものをセット
   await vars.buffers.set(
@@ -239,7 +240,7 @@ export const actionRemovePin = async (
   }
   // 既存メッセージの取得
   const timeline = await vars.buffers.get(denops, "channelTimeline");
-  ensureArray<Message>(timeline);
+  assert(timeline, is.ArrayOf(isMessage));
   message.pinned = false;
   // ピン留め解除したものをセット
   await vars.buffers.set(
diff --git a/denops/traqvim/deps.ts b/denops/traqvim/deps.ts
index f9b3f41..2c32e7d 100644
--- a/denops/traqvim/deps.ts
+++ b/denops/traqvim/deps.ts
@@ -2,11 +2,11 @@ export * as oauth2Client from "https://deno.land/x/oauth2_client@v1.0.0/mod.ts";
 export * as oak from "https://deno.land/x/oak@v6.3.0/mod.ts";
 export * as path from "https://deno.land/std@0.177.0/path/mod.ts";
 export {
-  ensureArray,
-  ensureNumber,
-  ensureObject,
-  ensureString,
-} from "https://deno.land/x/unknownutil@v1.0.0/mod.ts";
+  assert,
+  ensure,
+  is,
+} from "https://deno.land/x/unknownutil@v3.18.1/mod.ts";
+export type { Predicate } from "https://deno.land/x/unknownutil@v3.18.1/mod.ts";
 export type { Denops } from "https://deno.land/x/denops_std@v4.0.0/mod.ts";
 export * as fn from "https://deno.land/x/denops_std@v4.0.0/function/mod.ts";
 export * as vars from "https://deno.land/x/denops_std@v4.0.0/variable/mod.ts";
diff --git a/denops/traqvim/main.ts b/denops/traqvim/main.ts
index 7ef41c5..1f0e97f 100644
--- a/denops/traqvim/main.ts
+++ b/denops/traqvim/main.ts
@@ -8,13 +8,13 @@ import {
   sendMessage,
 } from "./model.ts";
 import {
+  assert,
   bufname,
   Denops,
-  ensureArray,
-  ensureNumber,
-  ensureString,
+  ensure,
   fn,
   helper,
+  is,
   vars,
 } from "./deps.ts";
 import {
@@ -31,10 +31,11 @@ import {
 } from "./action.ts";
 import { ChannelMessageBuffer, Message } from "./type.d.ts";
 import { api } from "./api.ts";
+import { isMessage } from "./type_check.ts";
 
 export async function main(denops: Denops) {
   const path = await vars.globals.get(denops, "traqvim#token_file_path");
-  ensureString(path);
+  assert(path, is.String);
   api.tokenFilePath = path;
   // oauthの仮オブジェクト
   let oauth: OAuth;
@@ -62,7 +63,7 @@ export async function main(denops: Denops) {
         "No",
         "Warning",
       );
-      ensureNumber(choice);
+      assert(choice, is.Number);
       switch (choice) {
         // dialogの中断
         case 0:
@@ -87,7 +88,7 @@ export async function main(denops: Denops) {
       const homePath = await homeChannelPath();
       const homeId = await homeChannelId();
       const limit = await vars.globals.get(denops, "traqvim#fetch_limit");
-      ensureNumber(limit);
+      assert(limit, is.Number);
       const timelineOption: channelMessageOptions = {
         id: homeId,
         channelPath: homePath,
@@ -99,7 +100,7 @@ export async function main(denops: Denops) {
       return;
     },
     async timeline(channelPath: unknown): Promise<unknown> {
-      ensureString(channelPath);
+      assert(channelPath, is.String);
       // '#gps/times/kamecha' → ['gps', 'times', 'kamecha']
       const channelPathArray = channelPath.substring(1).split("/");
       const channelID = await channelUUID(channelPathArray);
@@ -107,9 +108,9 @@ export async function main(denops: Denops) {
         helper.echo(denops, "Channel not found");
         return;
       }
-      ensureString(channelID);
+      assert(channelID, is.String);
       const limit = await vars.globals.get(denops, "traqvim#fetch_limit");
-      ensureNumber(limit);
+      assert(limit, is.Number);
       const timelineOption: channelMessageOptions = {
         id: channelID,
         channelPath: channelPath,
@@ -126,8 +127,8 @@ export async function main(denops: Denops) {
     },
     async reload(bufNum: unknown, bufName: unknown): Promise<unknown> {
       // バッファ番号は被らないが、バッファ名は被る可能性がある
-      ensureNumber(bufNum);
-      ensureString(bufName);
+      assert(bufNum, is.Number);
+      assert(bufName, is.String);
       const bufnameParsed = bufname.parse(bufName);
       if (bufnameParsed.expr === "/Activity") {
         actionOpenActivity(denops, bufNum);
@@ -137,9 +138,9 @@ export async function main(denops: Denops) {
         const bufNameWithoutNumber =
           bufnameParsed.fragment?.replace(/\(\d+\)$/, "") || "";
         const channelID = await vars.buffers.get(denops, "channelID");
-        ensureString(channelID);
+        assert(channelID, is.String);
         const limit = await vars.globals.get(denops, "traqvim#fetch_limit");
-        ensureNumber(limit);
+        assert(limit, is.Number);
         const timelineOption: channelMessageOptions = {
           id: channelID,
           channelPath: bufNameWithoutNumber,
@@ -152,17 +153,17 @@ export async function main(denops: Denops) {
       return;
     },
     async messageForward(bufNum: unknown, bufName: unknown): Promise<unknown> {
-      ensureNumber(bufNum);
-      ensureString(bufName);
+      assert(bufNum, is.Number);
+      assert(bufName, is.String);
       // 対応するバッファのメッセージの新しいメッセージの日付を取得
       try {
         const timeline = await vars.buffers.get(denops, "channelTimeline");
-        ensureArray<Message>(timeline);
+        assert(timeline, is.ArrayOf(isMessage));
         const bufNameWithoutNumber = bufName.replace(/\(\d+\)$/, "");
         const channelID = await vars.buffers.get(denops, "channelID");
-        ensureString(channelID);
+        assert(channelID, is.String);
         const limit = await vars.globals.get(denops, "traqvim#fetch_limit");
-        ensureNumber(limit);
+        assert(limit, is.Number);
         // 最後のメッセージの内容
         const timelineOption: channelMessageOptions = {
           id: channelID,
@@ -189,17 +190,17 @@ export async function main(denops: Denops) {
       }
     },
     async messageBack(bufNum: unknown, bufName: unknown): Promise<unknown> {
-      ensureNumber(bufNum);
-      ensureString(bufName);
+      assert(bufNum, is.Number);
+      assert(bufName, is.String);
       // 対応するバッファのメッセージの古いメッセージの日付を取得
       try {
         const timeline = await vars.buffers.get(denops, "channelTimeline");
-        ensureArray<Message>(timeline);
+        assert(timeline, is.ArrayOf(isMessage));
         const bufNameWithoutNumber = bufName.replace(/\(\d+\)$/, "");
         const channelID = await vars.buffers.get(denops, "channelID");
-        ensureString(channelID);
+        assert(channelID, is.String);
         const limit = await vars.globals.get(denops, "traqvim#fetch_limit");
-        ensureNumber(limit);
+        assert(limit, is.Number);
         // 最後のメッセージの内容
         const timelineOption: channelMessageOptions = {
           id: channelID,
@@ -224,10 +225,10 @@ export async function main(denops: Denops) {
       }
     },
     async messageOpen(bufNum: unknown, bufName: unknown): Promise<unknown> {
-      ensureNumber(bufNum);
-      ensureString(bufName);
+      assert(bufNum, is.Number);
+      assert(bufName, is.String);
       const channelID = await fn.getbufvar(denops, bufNum, "channelID");
-      ensureString(channelID);
+      assert(channelID, is.String);
       const channelMessageVars: ChannelMessageBuffer = {
         channelID: channelID,
       };
@@ -257,25 +258,27 @@ export async function main(denops: Denops) {
     },
     async messageSend(bufNum: unknown, contents: unknown): Promise<unknown> {
       helper.echo(denops, "Sending...");
-      ensureNumber(bufNum);
+      assert(bufNum, is.Number);
       const channelID = await fn.getbufvar(denops, bufNum, "channelID");
-      ensureString(channelID);
-      const content = (contents as string[]).join("\n");
+      assert(channelID, is.String);
+      const content = (ensure(contents, is.ArrayOf(is.String))).join("\n");
       await sendMessage(channelID, content);
       await denops.cmd(":bdelete");
       return;
     },
     async yankMessageLink(message: unknown): Promise<unknown> {
-      // ensureでの型チェックの仕方分からんから、とりあえずasで:awoo:
-      await actionYankMessageLink(denops, message as Message);
+      assert(message, isMessage);
+      await actionYankMessageLink(denops, message);
       return Promise.resolve();
     },
     async yankMessageMarkdown(message: unknown): Promise<unknown> {
-      await actionYankMessageMarkdown(denops, message as Message);
+      assert(message, isMessage);
+      await actionYankMessageMarkdown(denops, message);
       return Promise.resolve();
     },
     async messageDelete(bufNum: unknown, message: unknown): Promise<unknown> {
-      ensureNumber(bufNum);
+      assert(bufNum, is.Number);
+      assert(message, isMessage);
       const choice = await fn.confirm(
         denops,
         "Delete message?",
@@ -283,7 +286,7 @@ export async function main(denops: Denops) {
         "No",
         "Warning",
       );
-      ensureNumber(choice);
+      assert(choice, is.Number);
       switch (choice) {
         // dialogの中断
         case 0:
@@ -292,7 +295,7 @@ export async function main(denops: Denops) {
         // Yes
         case 1:
           helper.echo(denops, "delete message...");
-          await actionDeleteMessage(denops, message as Message, bufNum);
+          await actionDeleteMessage(denops, message, bufNum);
           break;
         // No
         case 2:
@@ -305,7 +308,7 @@ export async function main(denops: Denops) {
       return Promise.resolve();
     },
     async messageEditOpen(bufNum: unknown, message: unknown): Promise<unknown> {
-      ensureNumber(bufNum);
+      assert(bufNum, is.Number);
       const bufName = await fn.bufname(denops, bufNum);
       const messageBufName = bufname.format({
         scheme: bufname.parse(bufName).scheme,
@@ -316,7 +319,7 @@ export async function main(denops: Denops) {
         fragment: bufname.parse(bufName).fragment,
       });
       const messageBufNum = await fn.bufnr(denops, messageBufName, true);
-      ensureNumber(messageBufNum);
+      assert(messageBufNum, is.Number);
       await fn.setbufvar(denops, bufNum, "&splitbelow", 1);
       await denops.cmd(`split +buffer\\ ${messageBufNum}`);
       await fn.setbufvar(denops, bufNum, "&splitright", 0);
@@ -325,7 +328,7 @@ export async function main(denops: Denops) {
         denops,
         messageBufNum,
         1,
-        (message as Message).content.split("\n"),
+        (ensure(message, isMessage)).content.split("\n"),
       );
       await fn.setbufvar(
         denops,
@@ -349,9 +352,10 @@ export async function main(denops: Denops) {
       message: unknown,
       contents: unknown,
     ): Promise<unknown> {
-      ensureNumber(bufNum);
-      const content = (contents as string[]).join("\n");
-      await actionEditMessage(denops, message as Message, content, bufNum);
+      assert(bufNum, is.Number);
+      assert(message, isMessage);
+      const content = (ensure(contents, is.ArrayOf(is.String))).join("\n");
+      await actionEditMessage(denops, message, content, bufNum);
       await denops.cmd(":bdelete");
       return;
     },
@@ -359,16 +363,18 @@ export async function main(denops: Denops) {
       bufNum: unknown,
       message: unknown,
     ): Promise<unknown> {
-      ensureNumber(bufNum);
-      await actionCreatePin(denops, message as Message, bufNum);
+      assert(bufNum, is.Number);
+      assert(message, isMessage);
+      await actionCreatePin(denops, message, bufNum);
       return;
     },
     async removePin(
       bufNum: unknown,
       message: unknown,
     ): Promise<unknown> {
-      ensureNumber(bufNum);
-      await actionRemovePin(denops, message as Message, bufNum);
+      assert(bufNum, is.Number);
+      assert(message, isMessage);
+      await actionRemovePin(denops, message, bufNum);
       return;
     },
   };
diff --git a/denops/traqvim/model.ts b/denops/traqvim/model.ts
index 0265273..b46fc53 100644
--- a/denops/traqvim/model.ts
+++ b/denops/traqvim/model.ts
@@ -1,6 +1,6 @@
 import { api } from "./api.ts";
 import { Channel, Message, UnreadChannel } from "./type.d.ts";
-import { traq } from "./deps.ts";
+import { ensure, is, traq } from "./deps.ts";
 
 export type channelMessageOptions = {
   // channelUUID
@@ -133,7 +133,7 @@ export const homeChannelId = async (): Promise<string> => {
   if (me.homeChannel === null) {
     return "";
   }
-  return me.homeChannel as string;
+  return ensure(me.homeChannel, is.String);
 };
 
 // userIdからユーザー情報を取得する
diff --git a/denops/traqvim/type_check.ts b/denops/traqvim/type_check.ts
new file mode 100644
index 0000000..74585af
--- /dev/null
+++ b/denops/traqvim/type_check.ts
@@ -0,0 +1,70 @@
+import { ddcVim, is, Predicate, traq } from "./deps.ts";
+import { Message } from "./type.d.ts";
+
+const isPumHighlight: Predicate<ddcVim.PumHighlight> = is.ObjectOf({
+  name: is.String,
+  type: is.LiteralOneOf(["abbr", "kind", "menu"] as const),
+  hl_group: is.String,
+  col: is.Number,
+  width: is.Number,
+});
+
+export const isDdcItem: Predicate<ddcVim.Item> = is.ObjectOf({
+  word: is.String,
+  abbr: is.OptionalOf(is.String),
+  menu: is.OptionalOf(is.String),
+  info: is.OptionalOf(is.String),
+  kind: is.OptionalOf(is.String),
+  user_data: is.OptionalOf(is.Unknown),
+  highlights: is.OptionalOf(is.ArrayOf(isPumHighlight)),
+  columns: is.OptionalOf(is.RecordOf(is.String)),
+});
+
+export const isMessageStamp: Predicate<traq.MessageStamp> = is.ObjectOf({
+  userId: is.String,
+  stampId: is.String,
+  count: is.Number,
+  createdAt: is.String,
+  updatedAt: is.String,
+});
+
+const isUserAccountState: Predicate<traq.UserAccountState> = is.UnionOf([
+  // 停止
+  is.LiteralOf(0),
+  // 有効
+  is.LiteralOf(1),
+  // 一時停止
+  is.LiteralOf(2),
+]);
+
+const isUser: Predicate<traq.User> = is.ObjectOf({
+  id: is.String,
+  name: is.String,
+  displayName: is.String,
+  iconFileId: is.String,
+  bot: is.Boolean,
+  state: isUserAccountState,
+  updatedAt: is.String,
+});
+
+export const isMessage: Predicate<Message> = is.ObjectOf({
+  // traq.Message
+  id: is.String,
+  userId: is.String,
+  channelId: is.String,
+  content: is.String,
+  createdAt: is.String,
+  updatedAt: is.String,
+  pinned: is.Boolean,
+  stamps: is.ArrayOf(isMessageStamp),
+  threadId: is.UnionOf([is.String, is.Null]),
+
+  user: isUser,
+  position: is.OptionalOf(is.ObjectOf({
+    index: is.Number,
+    start: is.Number,
+    end: is.Number,
+  })),
+  // quote?: Message[];
+  quote: is.OptionalOf(is.ArrayOf((x: unknown): x is Message => isMessage(x))),
+});