diff --git a/tools/linter_lib/custom_check.py b/tools/linter_lib/custom_check.py
index 4d6b051d83..a183d8d9ed 100644
--- a/tools/linter_lib/custom_check.py
+++ b/tools/linter_lib/custom_check.py
@@ -120,6 +120,7 @@ js_rules = RuleList(
                 "web/src/types.ts",
                 "web/src/util.ts",
                 "web/src/message_helper.ts",
+                "web/src/server_message.ts",
                 "web/tests/",
             },
             "exclude_pattern": "emails",
diff --git a/tools/test-js-with-node b/tools/test-js-with-node
index f0cd746b2a..c3a24bc56c 100755
--- a/tools/test-js-with-node
+++ b/tools/test-js-with-node
@@ -204,6 +204,7 @@ EXEMPT_FILES = make_set(
         "web/src/sent_messages.ts",
         "web/src/sentry.ts",
         "web/src/server_events.js",
+        "web/src/server_message.ts",
         "web/src/settings.js",
         "web/src/settings_account.js",
         "web/src/settings_bots.js",
diff --git a/web/src/server_message.ts b/web/src/server_message.ts
new file mode 100644
index 0000000000..f1aa40fbae
--- /dev/null
+++ b/web/src/server_message.ts
@@ -0,0 +1,88 @@
+import {z} from "zod";
+
+const display_recipient_users_schema = z.object({
+    id: z.number(),
+    email: z.string(),
+    full_name: z.string(),
+    is_mirror_dummy: z.boolean(),
+});
+
+export const message_edit_history_schema = z.array(
+    z.object({
+        prev_content: z.optional(z.string()),
+        prev_rendered_content: z.optional(z.string()),
+        prev_rendered_content_version: z.optional(z.number()),
+        prev_stream: z.optional(z.number()),
+        prev_topic: z.optional(z.string()),
+        stream: z.optional(z.number()),
+        timestamp: z.number(),
+        topic: z.optional(z.string()),
+        user_id: z.number().nullable(),
+    }),
+);
+
+const message_reaction_schema = z.array(
+    z.object({
+        emoji_name: z.string(),
+        emoji_code: z.string(),
+        reaction_type: z.enum(["unicode_emoji", "realm_emoji", "zulip_extra_emoji"]),
+        user_id: z.number(),
+        user: z.object({
+            id: z.number(),
+            email: z.string(),
+            full_name: z.string(),
+            is_mirror_dummy: z.boolean().nullish(),
+        }),
+    }),
+);
+
+const submessage_schema = z.array(
+    z.object({
+        msg_type: z.string(),
+        content: z.string(),
+        message_id: z.number(),
+        sender_id: z.number(),
+        id: z.number(),
+    }),
+);
+
+export const server_message_schema = z
+    .object({
+        avatar_url: z.string().nullish(),
+        client: z.string(),
+        content: z.string(),
+        content_type: z.enum(["text/html", "text/x-markdown"]),
+        display_recipient: z.union([z.string(), z.array(display_recipient_users_schema)]),
+        edit_history: z.optional(message_edit_history_schema),
+        id: z.number(),
+        is_me_message: z.boolean(),
+        last_edit_timestamp: z.number().optional(),
+        reactions: message_reaction_schema,
+        recipient_id: z.number(),
+        sender_email: z.string(),
+        sender_full_name: z.string(),
+        sender_id: z.number(),
+        sender_realm_str: z.string(),
+        submessages: submessage_schema,
+        timestamp: z.number(),
+    })
+    .and(
+        z.discriminatedUnion("type", [
+            z.object({
+                type: z.literal("stream"),
+                subject: z.string(),
+                stream_id: z.number(),
+                topic_links: z.array(
+                    z.object({
+                        text: z.string(),
+                        url: z.string(),
+                    }),
+                ),
+            }),
+            z.object({
+                type: z.literal("private"),
+                subject: z.literal(""),
+                topic_links: z.array(z.never()),
+            }),
+        ]),
+    );