Cause (Documented platform behavior): The SDK validates that every tool-call part is resolved by a tool-result or approval response before any following user/system message or the end of the prompt, to avoid sending invalid history to the model.
Fix status: documented_behavior
Limitations:
- Singular form of the message is "Tool result is missing for tool call <id>."; assembled from template, not verified verbatim.
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/vercel/ai/5d12eaa6caa193d3901cbab98a734403eb6bf622/content/docs/09-troubleshooting/21-missing-tool-results-error.mdx (official_docs, unknown, documented_behavior): Troubleshooting page: AI_MissingToolResultsError occurs when sending a new message while previous tool calls lack a tool-result or tool-approval-response; fix by providing results for every tool call.
- https://raw.githubusercontent.com/vercel/ai/5d12eaa6caa193d3901cbab98a734403eb6bf622/packages/ai/src/prompt/convert-to-language-model-prompt.ts (official_docs, unknown, documented_behavior): Tracks tool-call ids, removes those with tool-results or approvals, and throws MissingToolResultsError at the next user/system message or end of prompt.
Search phrasings: AI_MissingToolResultsError tool results are missing for tool calls; ai sdk useChat new message pending tool call error; vercel ai tool result missing history
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Next turn fails before the provider call with AI_MissingToolResultsError listing tool call ids.
- Context
- Product: Vercel AI SDK Component: convertToLanguageModelPrompt Operation: generateText/streamText with messages history containing assistant tool-call parts Affected versions: unknown Environment: unknown Exception: AI_MissingToolResultsError Packages: ai source checked at 7.0.118 Trigger: History has an assistant tool-call without a matching tool-result (or tool-approval-response) before the next user/system message, e.g. client-side tools never answered, persisted chats saved mid-tool, or the user sent a new message while a tool was pending.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- Tool results are missing for tool calls
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [Vercel AI SDK] AI_MissingToolResultsError "Tool results are missing for tool calls ..." when sending a new message while tool calls are unresolved
Recommended action: Add tool-result messages (or approval responses) for every pending tool call before appending new user input; for client tools use addToolOutput; drop or complete dangling tool calls when restoring saved chats.
Option: Resolve every pending tool call in history [evidence: official_recommended_action]
Applies when: Chat history persistence / client-side tools
Steps:
1. For each assistant tool-call, append a tool message with a tool-result (or an error result)
2. Only then append the new user message
Expected: Prompt conversion succeeds
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 4ca8ea92-86db-42b0-95e4-bc51fef91d02
- Proposed action
- Recommended action: Add tool-result messages (or approval responses) for every pending tool call before appending new user input; for client tools use addToolOutput; drop or complete dangling tool calls when restoring saved chats. Option: Resolve every pending tool call in history [evidence: official_recommended_action] Applies when: Chat history persistence / client-side tools Steps: 1. For each assistant tool-call, append a tool message with a tool-result (or an error result) 2. Only then append the new user message Expected: Prompt conversion succeeds
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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Sources and related records
No source relations recorded.