From dcb56a07d9a9f0d61423e57e44ef340b8b54ff8e Mon Sep 17 00:00:00 2001
From: Minwook Shin <163576506+minwookshin@users.noreply.github.com>
Date: Wed, 16 Sep 2026 22:26:16 -0400
Subject: [PATCH] fix(tool): handle undefined input while streaming

---
 .../content/components/(chatbot)/tool.mdx     |  2 +-
 packages/elements/__tests__/tool.test.tsx     | 68 +++++++++++++++++++
 packages/elements/src/tool.tsx                | 24 ++++---
 packages/examples/src/tool.tsx                |  2 +-
 4 files changed, 85 insertions(+), 11 deletions(-)

diff --git a/apps/docs/content/components/(chatbot)/tool.mdx b/apps/docs/content/components/(chatbot)/tool.mdx
index a56f31c4..27fca941 100644
--- a/apps/docs/content/components/(chatbot)/tool.mdx
+++ b/apps/docs/content/components/(chatbot)/tool.mdx
@@ -277,7 +277,7 @@ Shows a tool that encountered an error during execution. Opens by default to dis
   type={{
     input: {
       description:
-        "The input parameters passed to the tool, displayed as formatted JSON.",
+        "The input parameters passed to the tool, displayed as formatted JSON. Renders nothing when input is undefined, such as before parameters arrive during input-streaming.",
       type: 'ToolUIPart["input"]',
     },
     "...props": {
diff --git a/packages/elements/__tests__/tool.test.tsx b/packages/elements/__tests__/tool.test.tsx
index a7225762..e47a6dbf 100644
--- a/packages/elements/__tests__/tool.test.tsx
+++ b/packages/elements/__tests__/tool.test.tsx
@@ -10,6 +10,19 @@ import {
 
 const QUERY_REGEX = /"query"/;
 
+const renderTool = (
+  input: unknown,
+  state: "input-streaming" | "input-available"
+) => (
+  <Tool defaultOpen>
+    <ToolHeader state={state} toolName="search" type="dynamic-tool" />
+    <ToolContent>
+      <ToolInput input={input} />
+      <ToolOutput errorText={undefined} output={undefined} />
+    </ToolContent>
+  </Tool>
+);
+
 describe("tool", () => {
   it("renders children", () => {
     render(<Tool>Content</Tool>);
@@ -182,6 +195,61 @@ describe("toolContent", () => {
 });
 
 describe("toolInput", () => {
+  it("renders nothing when input is undefined", () => {
+    const { container } = render(<ToolInput input={undefined} />);
+
+    expect(container).toBeEmptyDOMElement();
+  });
+
+  it("keeps the tool visible as input starts streaming and becomes available", () => {
+    const { container, rerender } = render(
+      renderTool(undefined, "input-streaming")
+    );
+
+    expect(
+      screen.getByRole("button", { name: "searchPending" })
+    ).toBeInTheDocument();
+    expect(screen.queryByText("Parameters")).not.toBeInTheDocument();
+
+    rerender(renderTool({ query: "test" }, "input-streaming"));
+
+    expect(container.querySelector("code")).toHaveTextContent('"test"');
+
+    rerender(renderTool({ query: "test search" }, "input-available"));
+
+    expect(
+      screen.getByRole("button", { name: "searchRunning" })
+    ).toBeInTheDocument();
+    expect(container.querySelector("code")).toHaveTextContent('"test search"');
+  });
+
+  it("removes previous parameters when a new input starts streaming", () => {
+    const { container, rerender } = render(
+      renderTool({ query: "test search" }, "input-available")
+    );
+
+    rerender(renderTool(undefined, "input-streaming"));
+
+    expect(
+      screen.getByRole("button", { name: "searchPending" })
+    ).toBeInTheDocument();
+    expect(screen.queryByText("Parameters")).not.toBeInTheDocument();
+    expect(container.querySelector("code")).not.toBeInTheDocument();
+  });
+
+  it.each([
+    { input: null, json: "null" },
+    { input: false, json: "false" },
+    { input: 0, json: "0" },
+    { input: "", json: '""' },
+    { input: {}, json: "{}" },
+  ])("renders defined input $json", ({ input, json }) => {
+    const { container } = render(<ToolInput input={input} />);
+
+    expect(screen.getByText("Parameters")).toBeInTheDocument();
+    expect(container.querySelector("code")).toHaveTextContent(json);
+  });
+
   it("renders input parameters", async () => {
     const input = { query: "test search" };
     render(
diff --git a/packages/elements/src/tool.tsx b/packages/elements/src/tool.tsx
index 9a22010e..3474453c 100644
--- a/packages/elements/src/tool.tsx
+++ b/packages/elements/src/tool.tsx
@@ -116,16 +116,22 @@ export type ToolInputProps = ComponentProps<"div"> & {
   input: ToolPart["input"];
 };
 
-export const ToolInput = ({ className, input, ...props }: ToolInputProps) => (
-  <div className={cn("space-y-2 overflow-hidden", className)} {...props}>
-    <h4 className="font-medium text-muted-foreground text-xs uppercase tracking-wide">
-      Parameters
-    </h4>
-    <div className="rounded-md bg-muted/50">
-      <CodeBlock code={JSON.stringify(input, null, 2)} language="json" />
+export const ToolInput = ({ className, input, ...props }: ToolInputProps) => {
+  if (input === undefined) {
+    return null;
+  }
+
+  return (
+    <div className={cn("space-y-2 overflow-hidden", className)} {...props}>
+      <h4 className="font-medium text-muted-foreground text-xs uppercase tracking-wide">
+        Parameters
+      </h4>
+      <div className="rounded-md bg-muted/50">
+        <CodeBlock code={JSON.stringify(input, null, 2)} language="json" />
+      </div>
     </div>
-  </div>
-);
+  );
+};
 
 export type ToolOutputProps = ComponentProps<"div"> & {
   output: ToolPart["output"];
diff --git a/packages/examples/src/tool.tsx b/packages/examples/src/tool.tsx
index d24d71aa..21323db1 100644
--- a/packages/examples/src/tool.tsx
+++ b/packages/examples/src/tool.tsx
@@ -57,7 +57,7 @@ const Example = () => (
         type="tool-database_query"
       />
       <ToolContent>
-        <ToolInput input={{}} />
+        <ToolInput input={undefined} />
       </ToolContent>
     </Tool>