diff --git a/app/editor/extensions/Suggestion.ts b/app/editor/extensions/Suggestion.ts
index b258b76cf1..97eb4ecf2b 100644
--- a/app/editor/extensions/Suggestion.ts
+++ b/app/editor/extensions/Suggestion.ts
@@ -46,7 +46,7 @@ export default class Suggestion<
         : `(?:${triggers.map(escapeRegExp).join("|")})`;
 
     this.openRegex = new RegExp(
-      `(?:^|\\s|\\(|[\\p{Script=Han}\\p{Script=Hiragana}\\p{Script=Katakana}\\p{Script=Hangul}])${triggerPattern}(${`[\\p{L}/\\p{M}\\d${
+      `(?:^|\\s|\\(|\\+|[\\p{Script=Han}\\p{Script=Hiragana}\\p{Script=Katakana}\\p{Script=Hangul}])${triggerPattern}(${`[\\p{L}/\\p{M}\\d${
         this.options.allowSpaces ? "\\s{1}" : ""
       }\\.\\-–_]+`})${this.options.requireSearchTerm ? "" : "?"}$`,
       "u"
diff --git a/app/scenes/Document/components/Comments/CommentForm.tsx b/app/scenes/Document/components/Comments/CommentForm.tsx
index 3b594da18a..4ecb53a4a0 100644
--- a/app/scenes/Document/components/Comments/CommentForm.tsx
+++ b/app/scenes/Document/components/Comments/CommentForm.tsx
@@ -8,6 +8,7 @@ import * as React from "react";
 import { useTranslation } from "react-i18next";
 import { toast } from "sonner";
 import { useTheme } from "styled-components";
+import { parseReactionShorthand } from "@shared/editor/lib/emoji";
 import type { ProsemirrorData } from "@shared/types";
 import { getEventFiles } from "@shared/utils/files";
 import { AttachmentValidation, CommentValidation } from "@shared/validations";
@@ -157,6 +158,30 @@ function CommentForm({
       return;
     }
 
+    // "+:emoji:" shorthand: react to the comment above instead of replying.
+    if (thread && !thread.isNew) {
+      const emoji = parseReactionShorthand(draft);
+      if (emoji) {
+        const target = comments
+          .inThread(thread.id)
+          .filter((comment) => !comment.isNew)
+          .pop();
+
+        if (target) {
+          onSaveDraft(undefined);
+          setForceRender((s) => ++s);
+          void target.addReaction({ emoji, user });
+          onSubmit?.();
+
+          // re-focus the comment editor
+          setTimeout(() => {
+            editorRef.current?.focusAtStart();
+          }, 0);
+          return;
+        }
+      }
+    }
+
     const commentDraft = draft;
     onSaveDraft(undefined);
     setForceRender((s) => ++s);
diff --git a/shared/editor/lib/emoji.test.ts b/shared/editor/lib/emoji.test.ts
index e6bc1664e2..68a4c94d0e 100644
--- a/shared/editor/lib/emoji.test.ts
+++ b/shared/editor/lib/emoji.test.ts
@@ -1,4 +1,10 @@
-import { getNameFromEmoji, getEmojiFromName, loadEmojiData } from "./emoji";
+import type { ProsemirrorData } from "../../types";
+import {
+  getNameFromEmoji,
+  getEmojiFromName,
+  loadEmojiData,
+  parseReactionShorthand,
+} from "./emoji";
 
 beforeAll(async () => {
   await loadEmojiData();
@@ -15,3 +21,91 @@ describe("getEmojiFromName", () => {
     expect(getEmojiFromName("thinking_face")).toBe("🤔");
   });
 });
+
+describe("parseReactionShorthand", () => {
+  const doc = (content: ProsemirrorData[]): ProsemirrorData => ({
+    type: "doc",
+    content,
+  });
+
+  const paragraph = (content: ProsemirrorData[]): ProsemirrorData => ({
+    type: "paragraph",
+    content,
+  });
+
+  const text = (value: string): ProsemirrorData => ({
+    type: "text",
+    text: value,
+  });
+
+  const emoji = (name: string): ProsemirrorData => ({
+    type: "emoji",
+    attrs: { "data-name": name },
+  });
+
+  it("resolves a '+' followed by an emoji node", () => {
+    expect(
+      parseReactionShorthand(doc([paragraph([text("+"), emoji("thumbs_up")])]))
+    ).toBe("👍");
+  });
+
+  it("ignores whitespace between the '+' and the emoji node", () => {
+    expect(
+      parseReactionShorthand(
+        doc([paragraph([text("+"), text(" "), emoji("thinking_face")])])
+      )
+    ).toBe("🤔");
+  });
+
+  it("resolves a custom emoji UUID to its UUID", () => {
+    const uuid = "550e8400-e29b-41d4-a716-446655440000";
+    expect(
+      parseReactionShorthand(doc([paragraph([text("+"), emoji(uuid)])]))
+    ).toBe(uuid);
+  });
+
+  it("resolves literal '+:shortcode:' text", () => {
+    expect(
+      parseReactionShorthand(doc([paragraph([text("+:thinking_face:")])]))
+    ).toBe("🤔");
+  });
+
+  it("returns undefined for an unknown shortcode", () => {
+    expect(
+      parseReactionShorthand(
+        doc([paragraph([text("+"), emoji("not_an_emoji")])])
+      )
+    ).toBeUndefined();
+  });
+
+  it("returns undefined when there is text alongside the emoji", () => {
+    expect(
+      parseReactionShorthand(
+        doc([paragraph([text("+ nice "), emoji("thumbs_up")])])
+      )
+    ).toBeUndefined();
+  });
+
+  it("returns undefined for a regular comment", () => {
+    expect(
+      parseReactionShorthand(doc([paragraph([text("Looks good to me")])]))
+    ).toBeUndefined();
+  });
+
+  it("returns undefined when the '+' prefix is missing", () => {
+    expect(
+      parseReactionShorthand(doc([paragraph([emoji("thumbs_up")])]))
+    ).toBeUndefined();
+  });
+
+  it("returns undefined for multiple paragraphs", () => {
+    expect(
+      parseReactionShorthand(
+        doc([
+          paragraph([text("+"), emoji("thumbs_up")]),
+          paragraph([text("more")]),
+        ])
+      )
+    ).toBeUndefined();
+  });
+});
diff --git a/shared/editor/lib/emoji.ts b/shared/editor/lib/emoji.ts
index f7cc870d97..988642dc8d 100644
--- a/shared/editor/lib/emoji.ts
+++ b/shared/editor/lib/emoji.ts
@@ -1,4 +1,6 @@
 import type { EmojiMartData } from "@emoji-mart/data";
+import { isUUID } from "validator";
+import type { ProsemirrorData } from "../../types";
 
 export const emojiMartToGemoji: Record<string, string> = {
   "+1": "thumbs_up",
@@ -74,3 +76,77 @@ export const getEmojiFromName = (name: string) =>
  */
 export const getNameFromEmoji = (emoji: string) =>
   Object.entries(nameToEmoji).find(([, value]) => value === emoji)?.[0];
+
+/**
+ * Resolve an emoji node name to the value used to react with.
+ *
+ * @param name The emoji shortcode, or a UUID for a custom emoji.
+ * @returns the native emoji character, the UUID of a custom emoji, or undefined
+ * when the name does not resolve to a known emoji.
+ */
+function getReactionFromName(name: unknown): string | undefined {
+  if (typeof name !== "string") {
+    return undefined;
+  }
+
+  // Custom emojis are stored as UUIDs and reacted with directly.
+  if (isUUID(name)) {
+    return name;
+  }
+
+  const character = getEmojiFromName(name);
+  return character === "?" ? undefined : character;
+}
+
+/**
+ * Detect the "+:emoji:" reaction shorthand within a comment's document. When a
+ * comment consists solely of a leading "+" immediately followed by a single
+ * emoji it is treated as a request to react to the comment above rather than as
+ * a new comment, mirroring the Slack shorthand.
+ *
+ * @param data The Prosemirror document of the draft comment.
+ * @returns the emoji to react with — a native emoji character, or a UUID for a
+ * custom emoji — or undefined when the document is not a reaction shorthand.
+ */
+export function parseReactionShorthand(
+  data: ProsemirrorData
+): string | undefined {
+  const blocks = data.content ?? [];
+  if (blocks.length !== 1) {
+    return undefined;
+  }
+
+  const paragraph = blocks[0];
+  if (paragraph.type !== "paragraph") {
+    return undefined;
+  }
+
+  // Ignore whitespace-only text nodes so that "+ :emoji:" still matches.
+  const inline = (paragraph.content ?? []).filter(
+    (node) => !(node.type === "text" && !node.text?.trim())
+  );
+
+  // The common case: a "+" text node followed by an emoji node inserted via
+  // the emoji menu.
+  if (inline.length === 2) {
+    const [prefix, emoji] = inline;
+    if (
+      prefix.type === "text" &&
+      prefix.text?.trim() === "+" &&
+      emoji.type === "emoji"
+    ) {
+      return getReactionFromName(emoji.attrs?.["data-name"]);
+    }
+    return undefined;
+  }
+
+  // Fallback: literal "+:shortcode:" text that was never converted to a node.
+  if (inline.length === 1 && inline[0].type === "text") {
+    const match = inline[0].text?.trim().match(/^\+\s*:([\w-]+):$/);
+    if (match) {
+      return getReactionFromName(match[1]);
+    }
+  }
+
+  return undefined;
+}