vercel/ai · error · UnsupportedFunctionalityError

allowedTools with only tools that cannot be allow-listed (${

Error message

allowedTools with only tools that cannot be allow-listed (${droppedToolNames.join(', ')})

What it means

When allowedTools is set, prepareResponsesTools filters the tool list down to entries that can actually be allow-listed on the Responses API (e.g. function-type tools). If every entry in allowedTools was dropped because its corresponding tool type cannot be allow-listed, the SDK throws UnsupportedFunctionalityError instead of silently sending an empty allow-list.

Source

Thrown at packages/openai/src/responses/openai-responses-prepare-tools.ts:486

        });
        continue;
      }

      if (!resolution.supported) {
        toolWarnings.push({
          type: 'unsupported',
          feature: `allowedTools entry "${name}"`,
          details: `${resolution.reason}; the tool is removed from the allowed tools`,
        });
        droppedToolNames.push(name);
        continue;
      }

      allowedToolEntries.push(resolution.entry);
    }

    if (allowedToolEntries.length === 0) {
      throw new UnsupportedFunctionalityError({
        functionality: `allowedTools with only tools that cannot be allow-listed (${droppedToolNames.join(
          ', ',
        )})`,
      });
    }

    return {
      tools: openaiTools,
      toolChoice: {
        type: 'allowed_tools',
        mode: allowedTools.mode ?? 'auto',
        tools: allowedToolEntries,
      },
      toolWarnings,
    };
  }

  if (toolChoice == null) {

View on GitHub (pinned to 69428b1f8b)

Solutions

1. Add at least one allow-listable (function) tool to the tools array and reference it in allowedTools
2. Remove non-allow-listable tool names from allowedTools and gate them via toolChoice or application logic instead
3. Convert the restricted capability into a custom function tool so it can be allow-listed

Example fix

// before
tools: { web_search: openai.tools.webSearch() },
allowedTools: ['web_search']
// after
tools: { web_search: openai.tools.webSearch(), search_wrapper: tool({...}) },
allowedTools: ['search_wrapper']

if (allowedTools.length > 0 && !allowedTools.some(name => name in functionTools)) {
  throw new Error('allowedTools must include at least one allow-listable function tool');
}

function hasAllowListableTool(tools: Record<string, unknown>, allowedTools: string[]): boolean {
  return allowedTools.some(name => tools[name] != null);
}

try {
  await generateText({ model: openai.responses('gpt-4.1'), tools, allowedTools, ... });
} catch (e) {
  if (UnsupportedFunctionalityError.isInstance(e) && e.message.includes('cannot be allow-listed')) {
    // fall back to calling without allowedTools and enforce restrictions app-side
  } else throw e;
}

When it happens

Trigger: Calling an openai.responses(...) model with allowedTools containing only names that resolve to tool types OpenAI cannot allow-list (e.g. web_search, code_interpreter or other built-in/hosted tools) and no allow-listable function tools.

Common situations: Restricting tools in an agent config where the only configured tools are built-in OpenAI tools; renaming a function tool so allowedTools no longer matches an allow-listable entry; copying an allowedTools list from a chat.completions setup to responses.

Related errors

• conflicting descriptions for OpenAI tool namespace "${namesp
• tool choice type: ${_exhaustiveCheck}
• non-streaming transcription with ${this.modelId}
• streaming transcription with ${this.modelId}
• 'text file parts' functionality not supported.

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/9ea1356ff37be5eb. Report an issue: GitHub.