diff --git a/src/domain/post.test.ts b/src/domain/post.test.ts
new file mode 100644
index 0000000..9431915
--- /dev/null
+++ b/src/domain/post.test.ts
@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+import { Post, PostArgs } from "./post.js";
+import { Snowflake } from "../helpers/id_generator.js";
+import { Media } from "./media.js";
+
+describe("Post", () => {
+  const defaultPostArgs: PostArgs = {
+    id: "10101450391945216" as Snowflake,
+    authorID: "10101451896913920" as Snowflake,
+    text: "Hello, world!",
+    visibility: 0,
+    createdAt: new Date(),
+    attachments: [],
+    reactions: [],
+  };
+
+  it("添付ファイルは16個以上添付できない", () => {
+    expect(() => {
+      new Post({
+        ...defaultPostArgs,
+        attachments: new Array(17).fill({} as Media),
+      });
+    }).toThrowError(
+      new Error(
+        "failed to create post: The number of attachments must be less than 16.",
+      ),
+    );
+  });
+
+  it("ファイルを添付できる", () => {
+    expect(() => {
+      new Post({
+        ...defaultPostArgs,
+        attachments: new Array(10).fill({} as Media),
+      });
+    }).toBeTruthy();
+  });
+});
diff --git a/src/domain/post.ts b/src/domain/post.ts
index 46bf32f..c949194 100644
--- a/src/domain/post.ts
+++ b/src/domain/post.ts
@@ -2,6 +2,16 @@ import { Snowflake } from "../helpers/id_generator.js";
 import { User } from "./user.js";
 import { Media } from "./media.js";
 
+export interface PostArgs {
+  id: Snowflake;
+  authorID: Snowflake;
+  text: string;
+  visibility: number;
+  createdAt: Date;
+  attachments: Array<Media>;
+  reactions: Array<PostReactionEvent>;
+}
+
 export class Post {
   get visibility(): number {
     return this._visibility;
@@ -54,6 +64,7 @@ export class Post {
     attachments: Array<Media>;
     reactions: Array<PostReactionEvent>;
   }) {
+    this.validate(args);
     this._id = args.id;
     this._authorID = args.authorID;
 
@@ -70,6 +81,14 @@ export class Post {
     }
     return text;
   }
+
+  private validate(args: PostArgs) {
+    if (args.attachments.length > 16) {
+      throw new Error(
+        "failed to create post: The number of attachments must be less than 16.",
+      );
+    }
+  }
 }
 
 export class PostReactionEvent {
diff --git a/src/domain/server.test.ts b/src/domain/server.test.ts
new file mode 100644
index 0000000..65274ce
--- /dev/null
+++ b/src/domain/server.test.ts
@@ -0,0 +1,116 @@
+import { describe, expect, it } from "vitest";
+import { Server, ServerArgs } from "./server.js";
+import { Snowflake } from "../helpers/id_generator.js";
+
+describe("Server", () => {
+  const defaultServerArgs: ServerArgs = {
+    id: "10101294855225344" as Snowflake,
+    host: "social.example.jp",
+    softwareName: "Mastodon",
+    softwareVersion: "4.0.0",
+    name: "example social",
+    description: "this is example social",
+    maintainer: "example maintainer",
+    maintainerEmail: "johndoe@example.jp",
+    iconURL: "https://social.example.jp/icon.png",
+    faviconURL: "https://social.example.jp/favicon.png",
+  };
+
+  it("128文字以上のホスト名は設定できない", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+        host: "a".repeat(128 + 1),
+      });
+    }).toThrowError(new Error("failed to create server: host is too long"));
+  });
+
+  it("4文字以下のホスト名は設定できない", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+        host: "a.b",
+      });
+    }).toThrowError(new Error("failed to create server: host is too short"));
+  });
+
+  it("ホスト名を設定できる", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+      });
+    }).toBeTruthy();
+  });
+
+  it("128文字以上のソフトウェア名は設定できない", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+        softwareName: "a".repeat(128 + 1),
+      });
+    }).toThrowError(
+      new Error("failed to create server: softwareName is too long"),
+    );
+  });
+
+  it("ソフトウェア名を設定できる", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+      });
+    }).toBeTruthy();
+  });
+
+  it("128文字以上のソフトウェアバージョンは設定できない", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+        softwareVersion: "a".repeat(128 + 1),
+      });
+    }).toThrowError(
+      new Error("failed to create server: softwareVersion is too long"),
+    );
+  });
+
+  it("128文字以上のサーバー名は設定できない", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+        name: "a".repeat(128 + 1),
+      });
+    }).toThrowError(new Error("failed to create server: name is too long"));
+  });
+
+  it("3000文字以上のサーバー説明文は設定できない", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+        description: "a".repeat(3000 + 1),
+      });
+    }).toThrowError(
+      new Error("failed to create server: description is too long"),
+    );
+  });
+
+  it("256文字以上の管理者名は設定できない", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+        maintainer: "a".repeat(256 + 1),
+      });
+    }).toThrowError(
+      new Error("failed to create server: maintainer is too long"),
+    );
+  });
+
+  it("256文字以上の管理者メールアドレスは設定できない", () => {
+    expect(() => {
+      new Server({
+        ...defaultServerArgs,
+        maintainerEmail: "a".repeat(256 + 1),
+      });
+    }).toThrowError(
+      new Error("failed to create server: maintainerEmail is too long"),
+    );
+  });
+});
diff --git a/src/domain/server.ts b/src/domain/server.ts
index af57074..12a2c61 100644
--- a/src/domain/server.ts
+++ b/src/domain/server.ts
@@ -1,5 +1,18 @@
 import { Snowflake } from "../helpers/id_generator.js";
 
+export interface ServerArgs {
+  id: Snowflake;
+  host: string;
+  softwareName: string;
+  softwareVersion: string;
+  name: string;
+  description: string;
+  maintainer: string;
+  maintainerEmail: string;
+  iconURL: string;
+  faviconURL: string;
+}
+
 export class Server {
   get softwareName(): string {
     return this._softwareName;
@@ -105,6 +118,8 @@ export class Server {
     iconURL: string;
     faviconURL: string;
   }) {
+    this.validate(args);
+
     this._id = args.id;
     this._host = args.host;
     this._softwareName = args.softwareName;
@@ -116,4 +131,36 @@ export class Server {
     this._iconURL = args.iconURL;
     this._faviconURL = args.faviconURL;
   }
+
+  private validate(args: ServerArgs) {
+    if ([...args.host].length > 128) {
+      throw new Error("failed to create server: host is too long");
+    } else if ([...args.host].length < 4) {
+      throw new Error("failed to create server: host is too short");
+    }
+
+    if ([...args.softwareName].length > 128) {
+      throw new Error("failed to create server: softwareName is too long");
+    }
+
+    if ([...args.softwareVersion].length > 128) {
+      throw new Error("failed to create server: softwareVersion is too long");
+    }
+
+    if ([...args.name].length > 128) {
+      throw new Error("failed to create server: name is too long");
+    }
+
+    if ([...args.description].length > 3000) {
+      throw new Error("failed to create server: description is too long");
+    }
+
+    if ([...args.maintainer].length > 256) {
+      throw new Error("failed to create server: maintainer is too long");
+    }
+
+    if ([...args.maintainerEmail].length > 256) {
+      throw new Error("failed to create server: maintainerEmail is too long");
+    }
+  }
 }
diff --git a/src/domain/user.test.ts b/src/domain/user.test.ts
new file mode 100644
index 0000000..664a152
--- /dev/null
+++ b/src/domain/user.test.ts
@@ -0,0 +1,101 @@
+import { describe, expect, it } from "vitest";
+import { User, UserAPData } from "./user.js";
+import { Snowflake } from "../helpers/id_generator.js";
+
+describe("User domain model", () => {
+  const defaultDataArgs = {
+    id: "10100912877076480" as Snowflake,
+    serverID: "10100914303139840" as Snowflake,
+    handle: "test",
+    fullHandle: "test@example.jp",
+    nickName: "TestUser",
+    bio: "testのユーザーです",
+    headerImageURL: "https://image.example.jp/header.png",
+    iconImageURL: "https://image.example.jp/icon.png",
+    password: "efnrkgnjkneiug",
+    role: 0,
+    createdAt: new Date(),
+    isLocalUser: true,
+    following: [],
+    apData: new UserAPData({
+      followersURL: "https://example.jp/followers",
+      followingURL: "https://example.jp/following",
+      inboxURL: "https://example.jp/inbox",
+      outboxURL: "https://example.jp/outbox",
+      privateKey: "",
+      publicKey: "",
+      userAPID: "10100938952278016",
+      userID: "10100912877076480" as Snowflake,
+    }),
+  };
+
+  it("64文字以内の表示名は設定できる", () => {
+    const u = new User({ ...defaultDataArgs, nickName: "テストユーザー" });
+    expect(u).toBeTruthy();
+  });
+
+  it("64文字以上の表示名は設定できない", () => {
+    expect(
+      () =>
+        new User({
+          ...defaultDataArgs,
+          nickName: "テストユーザー".repeat(10),
+        }),
+    ).toThrowError(new Error("failed to create user: nickname is too long"));
+  });
+
+  it("64文字以上のハンドルは設定できない", () => {
+    expect(
+      () =>
+        new User({
+          ...defaultDataArgs,
+          handle: "test_user".repeat(20),
+        }),
+    ).toThrowError(new Error("failed to create user: handle is too long"));
+  });
+
+  it("64文字以下のハンドルを設定できる", () => {
+    expect(new User({ ...defaultDataArgs, handle: "test_user" })).toBeTruthy();
+  });
+
+  it("空文字列は設定できない", () => {
+    expect(() => new User({ ...defaultDataArgs, handle: "" })).toThrowError(
+      new Error("failed to create user: handle is too short"),
+    );
+  });
+
+  it("フルハンドルを設定できる", () => {
+    expect(
+      new User({ ...defaultDataArgs, fullHandle: "test@social.example.jp" }),
+    ).toBeTruthy();
+  });
+
+  it("FQDNとして成立しない長さのフルハンドルは設定できない", () => {
+    expect(
+      () =>
+        new User({
+          ...defaultDataArgs,
+          fullHandle: "t@a.b",
+        }),
+    ).toThrowError(new Error("failed to create user: fullHandle is too short"));
+  });
+
+  it("3000文字以上のbioは設定できない", () => {
+    expect(
+      () =>
+        new User({
+          ...defaultDataArgs,
+          bio: "a".repeat(3001),
+        }),
+    ).toThrowError(new Error("failed to create user: bio is too long"));
+  });
+
+  it("bioを設定できる", () => {
+    expect(
+      new User({
+        ...defaultDataArgs,
+        bio: "テストユーザーです",
+      }),
+    ).toBeTruthy();
+  });
+});
diff --git a/src/domain/user.ts b/src/domain/user.ts
index bb38c1b..2dd823d 100644
--- a/src/domain/user.ts
+++ b/src/domain/user.ts
@@ -1,6 +1,23 @@
 // ユーザー
 import { Snowflake } from "../helpers/id_generator.js";
 
+export interface UserArgs {
+  id: Snowflake;
+  handle: string;
+  fullHandle: string;
+  serverID: Snowflake;
+  nickName: string;
+  role: number;
+  bio: string;
+  headerImageURL: string;
+  iconImageURL: string;
+  password: string;
+  isLocalUser: boolean;
+  createdAt: Date;
+  apData: UserAPData;
+  following: Array<UserFollowEvent>;
+}
+
 export class User {
   get id(): Snowflake {
     return this._id;
@@ -70,10 +87,6 @@ export class User {
     return this._createdAt;
   }
 
-  set createdAt(value: Date) {
-    this._createdAt = value;
-  }
-
   get apData(): UserAPData {
     return this._apData;
   }
@@ -133,28 +146,16 @@ export class User {
   // フォロー中のユーザー
   private _following: Set<UserFollowEvent>;
 
-  constructor(args: {
-    id: Snowflake;
-    handle: string;
-    fullHandle: string;
-    serverID: Snowflake;
-    nickName: string;
-    role: number;
-    bio: string;
-    headerImageURL: string;
-    iconImageURL: string;
-    password: string;
-    isLocalUser: boolean;
-    createdAt: Date;
-    apData: UserAPData;
-    following: Array<UserFollowEvent>;
-  }) {
+  constructor(args: UserArgs) {
+    this.validate(args);
+
     // 不変
     this._id = args.id;
     this._handle = args.handle;
     this._fullHandle = args.fullHandle;
     this._isLocalUser = args.isLocalUser;
     this._serverID = args.serverID;
+    this._createdAt = args.createdAt;
 
     this._nickName = args.nickName;
     this._role = args.role;
@@ -162,10 +163,36 @@ export class User {
     this._password = args.password;
     this._headerImageURL = args.headerImageURL;
     this._iconImageURL = args.iconImageURL;
-    this._createdAt = args.createdAt;
     this._apData = args.apData;
     this._following = new Set(args.following);
   }
+
+  private validate(args: UserArgs) {
+    if ([...args.nickName].length > 64) {
+      throw new Error("failed to create user: nickname is too long");
+    } else if ([...args.nickName].length < 1) {
+      throw new Error("failed to create user: nickname is too short");
+    }
+
+    if ([...args.handle].length > 64) {
+      throw new Error("failed to create user: handle is too long");
+    } else if ([...args.handle].length < 1) {
+      throw new Error("failed to create user: handle is too short");
+    }
+
+    // ホスト名は最小4文字, @で1文字、ハンドルが最小1文字: 合計6文字以上
+    if ([...args.fullHandle].length < 6) {
+      throw new Error("failed to create user: fullHandle is too short");
+    }
+
+    if ([...args.bio].length > 3000) {
+      throw new Error("failed to create user: bio is too long");
+    }
+
+    if (args.isLocalUser && args.password.length < 1) {
+      throw new Error("failed to create user: password is not set");
+    }
+  }
 }
 
 export class UserAPData {
diff --git a/src/service/user/create_follow_service.test.ts b/src/service/user/create_follow_service.test.ts
index 10afbe5..f949d38 100644
--- a/src/service/user/create_follow_service.test.ts
+++ b/src/service/user/create_follow_service.test.ts
@@ -9,7 +9,7 @@ describe("create_follow_service", () => {
     new User({
       id: "1" as Snowflake,
       fullHandle: "testuser@example.com",
-      password: "",
+      password: "testUserPassword",
       role: 0,
       nickName: "test",
       handle: "test",
@@ -34,7 +34,7 @@ describe("create_follow_service", () => {
     new User({
       id: "2" as Snowflake,
       fullHandle: "testuser2@example.com",
-      password: "",
+      password: "testuser2password",
       role: 0,
       nickName: "test",
       handle: "test",