ToolInput crashes the tree while tool input is streaming (input is undefined, CodeBlock calls code.split)

Open Beginner friendly
#490 0 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
88/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
react, typescript
Domain
frontend

Research direction

Start in tool.tsx at ToolInput and trace its input into CodeBlockContent in code-block.tsx, especially createRawTokens and the useMemo. Reproduce the input-streaming sequence with undefined input, then verify the tool card and surrounding chat continue rendering through input-available without a split-related error.

Written by the indexing model from the issue text.

Description

Components: tool.tsx (ToolInput), code-block.tsx (CodeBlockContent)

What happens

While a tool part is in input-streaming, part.input is undefined. ToolInput renders <CodeBlock code={JSON.stringify(input, null, 2)} /> (tool.tsx:125); JSON.stringify(undefined) returns undefined, and createRawTokens calls code.split("\n") on it (code-block.tsx:171, from the useMemo at :384):

TypeError: Cannot read properties of undefined (reading 'split')
  createRawTokens   src/components/ai-elements/code-block.tsx:171
  CodeBlockContent  src/components/ai-elements/code-block.tsx:384

React unmounts the tree, so the whole chat stops rendering, not just the tool card. The props type allows it: ToolPart["input"] is unknown.

Repro

Render a tool part in every state:

<Tool>
  <ToolHeader type="dynamic-tool" state={part.state} toolName={part.toolName} />
  <ToolContent>
    <ToolInput input={part.input} />
    <ToolOutput output={part.output} errorText={part.errorText} />
  </ToolContent>
</Tool>

and stream a tool call whose input arrives in deltas. Observed stream: tool-input-start → tool-input-delta → tool-input-available; the crash happens on the render between the first two.

Observed with @ai-sdk/langchain 3.0.99, ai 7.0.99, @ai-sdk/react 4.0.102, React 19.3.0, Vite 8.3.0, components added from the @ai-elements registry on 2026-09-13. The same code is on main today. The throw is in render code, so the framework should not matter.

Workaround

Render ToolInput only once the input exists: {part.input !== undefined && <ToolInput input={part.input} />}.

Possible fix

Return null (or a pending placeholder) from ToolInput when input === undefined, or make CodeBlock tolerate a non-string code.

Dominant language
TypeScript
Stars
2.4k
Forks
283
Avg merge
32m
Merged PRs (30d)
1

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from vercel/ai-elements

All issues in vercel/ai-elements

Similar issues

More TypeScript issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.