diff --git a/app/src/lib/tributary.test.ts b/app/src/lib/tributary.test.ts
index ec2522d..90d2442 100644
--- a/app/src/lib/tributary.test.ts
+++ b/app/src/lib/tributary.test.ts
@@ -1,12 +1,3 @@
-import { describe, it, expect } from "vitest";
-import {
-  toStroops,
-  fromStroops,
-  formatAmount,
-  shortAddress,
-  recipientLabel,
-  ConversionError,
-} from "./tributary";
 import { describe, expect, it } from "vitest";
 import {
   ConversionError,
@@ -296,35 +287,4 @@ describe("Token conversion functions", () => {
   });
 });
 
-describe("formatAmount", () => {
-  it("formats valid decimal string with commas", () => {
-    expect(formatAmount("1000")).toBe("1,000");
-  });
-
-  it("returns input string if non-numeric", () => {
-    expect(formatAmount("abc")).toBe("abc");
-  });
-});
-
-describe("shortAddress", () => {
-  it("shortens stellar address", () => {
-    expect(
-      shortAddress("GBRPYHIL2CI3FNQ4BXLFMNDLFJUNPU2HY3ZMFXYFTRE65OTHVRWPAHV7")
-    ).toBe("GBRP…AHV7");
-  });
-});
 
-describe("recipientLabel", () => {
-  it("formats account recipient", () => {
-    expect(
-      recipientLabel({
-        tag: "Account",
-        values: ["GBRPYHIL2CI3FNQ4BXLFMNDLFJUNPU2HY3ZMFXYFTRE65OTHVRWPAHV7"],
-      })
-    ).toBe("GBRP…AHV7");
-  });
-
-  it("formats split recipient", () => {
-    expect(recipientLabel({ tag: "Split", values: [42n] })).toBe("split #42");
-  });
-});
diff --git a/contracts/splitter/src/lib.rs b/contracts/splitter/src/lib.rs
index 6388a7f..89d2ecb 100644
--- a/contracts/splitter/src/lib.rs
+++ b/contracts/splitter/src/lib.rs
@@ -594,6 +594,10 @@ impl Splitter {
         load(&env, id)
     }
 
+    pub fn is_locked(env: Env, id: u64) -> Result<bool, Error> {
+        Ok(load(&env, id)?.controller.is_none())
+    }
+
     pub fn recipient_count(env: Env, id: u64) -> Result<u32, Error> {
         Ok(load(&env, id)?.recipients.len())
     }
diff --git a/contracts/splitter/src/test.rs b/contracts/splitter/src/test.rs
index 2533347..c0a71d3 100644
--- a/contracts/splitter/src/test.rs
+++ b/contracts/splitter/src/test.rs
@@ -1923,3 +1923,28 @@ fn single_recipient_gets_full_amount() {
     assert_eq!(token_client.balance(&a), amount);
     assert_eq!(token_client.balance(&payer), 0);
 }
+
+#[test]
+fn is_locked_works() {
+    let s = setup();
+    let creator = Address::generate(&s.env);
+    let a = Address::generate(&s.env);
+    let b = Address::generate(&s.env);
+    let controller = Address::generate(&s.env);
+
+    let id_mutable = s.client.create_split(
+        &creator,
+        &vec![&s.env, acct(&a), acct(&b)],
+        &vec![&s.env, 5_000, 5_000],
+        &Some(controller.clone()),
+    );
+    assert!(!s.client.is_locked(&id_mutable));
+
+    let id_locked = s.client.create_split(
+        &creator,
+        &vec![&s.env, acct(&a), acct(&b)],
+        &vec![&s.env, 5_000, 5_000],
+        &None,
+    );
+    assert!(s.client.is_locked(&id_locked));
+}