vercel/ai · error · UnsupportedFunctionalityError

unsupported tool content part type: ${contentPart.type}

Error message

unsupported tool content part type: ${contentPart.type}

What it means

The tool-result content converter throws UnsupportedFunctionalityError for any content part whose type is not one of the handled kinds (text, file, etc.). Bedrock's Converse API only supports a fixed set of tool result content block types, so unknown part types are rejected at conversion time.

Source

Thrown at packages/amazon-bedrock/src/convert-to-amazon-bedrock-chat-messages.ts:473

                                      ),
                                    name: contentPart.filename
                                      ? stripFileExtension(contentPart.filename)
                                      : generateDocumentName(),
                                    source: {
                                      bytes: convertToBase64(
                                        contentPart.data.data,
                                      ),
                                    },
                                    ...(enableCitations && {
                                      citations: { enabled: true },
                                    }),
                                  },
                                };
                              }
                            }
                          }
                          default: {
                            throw new UnsupportedFunctionalityError({
                              functionality: `unsupported tool content part type: ${contentPart.type}`,
                            });
                          }
                        }
                      }),
                    );
                    break;
                  }
                  case 'text':
                  case 'error-text':
                    toolResultContent = [{ text: output.value }];
                    break;
                  case 'execution-denied':
                    toolResultContent = [
                      { text: output.reason ?? 'Tool call execution denied.' },
                    ];
                    break;
                  case 'json':

View on GitHub (pinned to 69428b1f8b)

Solutions

Only return 'text' (and supported 'file') content parts from tools when using Bedrock.
Convert unsupported part types to text (e.g. describe or serialize the content) before returning them.
Upgrade @ai-sdk/amazon-bedrock in case support for the part type was added.
If images are needed, return them as message content parts rather than tool result parts.

Example fix

// before
{ role: 'tool', content: [{ type: 'image', image: bytes }] }
// after
{ role: 'tool', content: [{ type: 'text', text: 'Screenshot captured (see description)...' }] }

Defensive patterns

Strategy: validation

Validate before calling

const BEDROCK_TOOL_RESULT_PART_TYPES = new Set(['text', 'file']);
function validateToolResultContent(content) {
  for (const part of content) {
    if (!BEDROCK_TOOL_RESULT_PART_TYPES.has(part.type)) {
      throw new Error(`Part type '${part.type}' unsupported in Bedrock tool results`);
    }
  }
}

Type guard

function isBedrockToolResultPart(part) {
  return part.type === 'text' || part.type === 'file';
}

Try / catch

try {
  await generateText({ model, messages });
} catch (error) {
  if (UnsupportedFunctionalityError.isInstance(error) && error.message.includes('unsupported tool content part type')) {
    console.error('Tool emitted a part type Bedrock cannot represent; serialize it to text.');
  }
  throw error;
}

Prevention

Restrict tool return shapes to text (and supported file) parts for Bedrock deployments.
Normalize tool outputs with a provider-specific adapter before returning them.
Check release notes when upgrading the SDK for new tool result part types.

When it happens

Trigger: Including a content part of an unhandled type (e.g. 'image' or a future/custom part type) inside a tool result's content array when targeting Bedrock.

Common situations: Tool results written for another provider (which may accept images or richer parts) are reused with Bedrock; or SDK version drift introduces new part types the converter does not handle yet.

Related errors

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/3f3a7ef4bd0a8cab. Report an issue: GitHub.