diff --git a/frontend/__tests__/test/funbox/funbox-functions.spec.ts b/frontend/__tests__/test/funbox/funbox-functions.spec.ts
new file mode 100644
index 000000000000..5bbd0b52fd45
--- /dev/null
+++ b/frontend/__tests__/test/funbox/funbox-functions.spec.ts
@@ -0,0 +1,60 @@
+import { describe, it, expect } from "vitest";
+import {
+  getFunboxFunctions,
+  FunboxFunctions,
+} from "../../../src/ts/test/funbox/funbox-functions";
+
+describe("funbox functions", () => {
+  describe("l33t funbox", () => {
+    const funboxFunctions = getFunboxFunctions();
+    const l33tFunbox = funboxFunctions.l33t as Required<
+      Pick<FunboxFunctions, "alterText">
+    >;
+
+    const alterText = (word: string): string =>
+      l33tFunbox.alterText(word, 0, word.length);
+
+    it("should convert lowercase letters to l33t speak", () => {
+      expect(alterText("hello world")).toBe("h3110 w0r1d");
+    });
+
+    it("should handle uppercase letters", () => {
+      expect(alterText("Hello")).toBe("H3110");
+    });
+
+    it("should handle mixed case", () => {
+      expect(alterText("HeLLo")).toBe("H3110");
+    });
+
+    it("should keep non-letter characters unchanged", () => {
+      expect(alterText("h3llo!")).toBe("h3110!");
+    });
+
+    it("should handle spaces", () => {
+      const result = alterText("hello world");
+      expect(result.startsWith("h3110 ")).toBe(true);
+      expect(result.endsWith("w0r1d")).toBe(true);
+      expect(result).not.toContain("/");
+    });
+
+    it("should handle all l33t characters", () => {
+      expect(alterText("abcdefg")).toBe("4bcd3f6");
+    });
+
+    it("should handle all l33t characters (uppercase)", () => {
+      expect(alterText("ABCDEFG")).toBe("4BCD3F6");
+    });
+
+    it("should convert xyz to l33t", () => {
+      expect(alterText("xyz")).toBe("xy2");
+    });
+
+    it("should handle empty string", () => {
+      expect(alterText("")).toBe("");
+    });
+
+    it("should handle string with no letters", () => {
+      expect(alterText("123 !@#")).toBe("123 !@#");
+    });
+  });
+});
diff --git a/frontend/src/ts/test/funbox/funbox-functions.ts b/frontend/src/ts/test/funbox/funbox-functions.ts
index 7430c0b6bae6..5d229e007fbd 100644
--- a/frontend/src/ts/test/funbox/funbox-functions.ts
+++ b/frontend/src/ts/test/funbox/funbox-functions.ts
@@ -173,6 +173,19 @@ export class PolyglotWordset extends Wordset {
   }
 }
 
+const l33tMap: Record<string, string> = {
+  a: "4",
+  e: "3",
+
+  g: "6",
+  i: "1",
+  l: "1",
+  o: "0",
+  s: "5",
+  t: "7",
+  z: "2",
+};
+
 const list: Partial<Record<FunboxName, FunboxFunctions>> = {
   "58008": {
     getWord(): string {
@@ -650,6 +663,13 @@ const list: Partial<Record<FunboxName, FunboxFunctions>> = {
       return word.toUpperCase();
     },
   },
+  l33t: {
+    alterText(word: string): string {
+      return word.replace(/[a-zA-Z]/g, (ch) => {
+        return l33tMap[ch.toLowerCase()] ?? ch;
+      });
+    },
+  },
   polyglot: {
     async withWords(_words) {
       const promises = Config.customPolyglot.map(async (language) =>
diff --git a/packages/funbox/src/list.ts b/packages/funbox/src/list.ts
index 866decc7d7e7..179ba6a29727 100644
--- a/packages/funbox/src/list.ts
+++ b/packages/funbox/src/list.ts
@@ -480,6 +480,14 @@ const list: Record<FunboxName, FunboxMetadata> = {
     difficultyLevel: 0,
     name: "no_quit",
   },
+  l33t: {
+    description: "1 533t 5p34k. C0nv3r7 7h3 73x7 70 l337.",
+    canGetPb: true,
+    difficultyLevel: 1,
+    properties: ["changesCapitalisation"],
+    frontendFunctions: ["alterText"],
+    name: "l33t",
+  },
 };
 
 export function getObject(): Record<FunboxName, FunboxMetadata> {
diff --git a/packages/schemas/src/configs.ts b/packages/schemas/src/configs.ts
index 36c979dafcde..ff104b021388 100644
--- a/packages/schemas/src/configs.ts
+++ b/packages/schemas/src/configs.ts
@@ -334,6 +334,7 @@ export const FunboxNameSchema = z.enum([
   "polyglot",
   "asl",
   "rot13",
+  "l33t",
   "no_quit",
 ]);
 export type FunboxName = z.infer<typeof FunboxNameSchema>;