diff --git a/src/discord/guild-emoji-cache.ts b/src/discord/guild-emoji-cache.ts
new file mode 100644
index 0000000000000..dd9432d4d324a
--- /dev/null
+++ b/src/discord/guild-emoji-cache.ts
@@ -0,0 +1,76 @@
+import { RequestClient } from "@buape/carbon";
+import { Routes } from "discord-api-types/v10";
+
+interface GuildEmoji {
+  id: string;
+  name: string;
+}
+
+interface CacheEntry {
+  emojis: GuildEmoji[];
+  fetchedAt: number;
+}
+
+const CACHE_TTL_MS = 5 * 60 * 1000; // 5 minutes
+
+const guildEmojiCache = new Map<string, CacheEntry>();
+
+async function getGuildEmojis(rest: RequestClient, guildId: string): Promise<GuildEmoji[]> {
+  const cached = guildEmojiCache.get(guildId);
+  if (cached && Date.now() - cached.fetchedAt < CACHE_TTL_MS) {
+    return cached.emojis;
+  }
+  const raw = (await rest.get(Routes.guildEmojis(guildId))) as Array<{
+    id?: string;
+    name?: string;
+  }>;
+  const emojis = (raw ?? [])
+    .filter((e): e is { id: string; name: string } => Boolean(e.id && e.name))
+    .map((e) => ({ id: e.id, name: e.name }));
+  guildEmojiCache.set(guildId, { emojis, fetchedAt: Date.now() });
+  return emojis;
+}
+
+function isPlainEmojiName(raw: string): boolean {
+  return /^[a-zA-Z0-9_]+$/.test(raw);
+}
+
+async function getGuildIdFromChannel(
+  rest: RequestClient,
+  channelId: string,
+): Promise<string | null> {
+  try {
+    const channel = (await rest.get(Routes.channel(channelId))) as { guild_id?: string };
+    return channel.guild_id ?? null;
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Resolve a plain emoji name to `name:id` format using guild emoji lookup.
+ * Returns the original string unchanged for unicode emoji, name:id, or <:name:id> formats.
+ */
+export async function resolveGuildEmoji(
+  rest: RequestClient,
+  channelId: string,
+  emoji: string,
+): Promise<string> {
+  const trimmed = emoji.trim();
+  if (!isPlainEmojiName(trimmed)) {
+    return emoji;
+  }
+
+  const guildId = await getGuildIdFromChannel(rest, channelId);
+  if (!guildId) {
+    return emoji;
+  }
+
+  const emojis = await getGuildEmojis(rest, guildId);
+  const match = emojis.find((e) => e.name === trimmed);
+  if (!match) {
+    return emoji;
+  }
+
+  return `${match.name}:${match.id}`;
+}
diff --git a/src/discord/send.reactions.ts b/src/discord/send.reactions.ts
index 436d64ac5b2ec..71441fcb6a5e4 100644
--- a/src/discord/send.reactions.ts
+++ b/src/discord/send.reactions.ts
@@ -1,5 +1,6 @@
 import { Routes } from "discord-api-types/v10";
 import { loadConfig } from "../config/config.js";
+import { resolveGuildEmoji } from "./guild-emoji-cache.js";
 import {
   buildReactionIdentifier,
   createDiscordClient,
@@ -16,7 +17,8 @@ export async function reactMessageDiscord(
 ) {
   const cfg = opts.cfg ?? loadConfig();
   const { rest, request } = createDiscordClient(opts, cfg);
-  const encoded = normalizeReactionEmoji(emoji);
+  const resolved = await resolveGuildEmoji(rest, channelId, emoji);
+  const encoded = normalizeReactionEmoji(resolved);
   await request(
     () => rest.put(Routes.channelMessageOwnReaction(channelId, messageId, encoded)),
     "react",
diff --git a/src/discord/send.sends-basic-channel-messages.test.ts b/src/discord/send.sends-basic-channel-messages.test.ts
index 58b8e3799b7f2..400283dee99e0 100644
--- a/src/discord/send.sends-basic-channel-messages.test.ts
+++ b/src/discord/send.sends-basic-channel-messages.test.ts
@@ -385,6 +385,37 @@ describe("reactMessageDiscord", () => {
       Routes.channelMessageOwnReaction("chan1", "msg1", "party_blob%3A123"),
     );
   });
+
+  it("resolves plain emoji name via guild lookup", async () => {
+    const { rest, putMock, getMock } = makeDiscordRest();
+    getMock.mockResolvedValueOnce({ guild_id: "guild1" });
+    getMock.mockResolvedValueOnce([
+      { id: "999", name: "fatbiden" },
+      { id: "888", name: "stonks" },
+    ]);
+    await reactMessageDiscord("chan1", "msg1", "fatbiden", { rest, token: "t" });
+    expect(putMock).toHaveBeenCalledWith(
+      Routes.channelMessageOwnReaction("chan1", "msg1", "fatbiden%3A999"),
+    );
+  });
+
+  it("passes through plain name when guild lookup fails", async () => {
+    const { rest, putMock, getMock } = makeDiscordRest();
+    getMock.mockRejectedValueOnce(new Error("not found"));
+    await reactMessageDiscord("chan1", "msg1", "fatbiden", { rest, token: "t" });
+    expect(putMock).toHaveBeenCalledWith(
+      Routes.channelMessageOwnReaction("chan1", "msg1", "fatbiden"),
+    );
+  });
+
+  it("passes through name:id format without extra lookup", async () => {
+    const { rest, putMock, getMock } = makeDiscordRest();
+    await reactMessageDiscord("chan1", "msg1", "fatbiden:999", { rest, token: "t" });
+    expect(getMock).not.toHaveBeenCalled();
+    expect(putMock).toHaveBeenCalledWith(
+      Routes.channelMessageOwnReaction("chan1", "msg1", "fatbiden%3A999"),
+    );
+  });
 });
 
 describe("removeReactionDiscord", () => {