vercel/ai · error · UnsupportedFunctionalityError

tool result file data of type "${contentPart.data.type}"

Error message

tool result file data of type "${contentPart.data.type}"

What it means

In tool-result conversion, a file part is only accepted when it is inline 'data' or an 's3:' protocol URL. Any other type (e.g. a plain https URL, or other data carrier types) triggers UnsupportedFunctionalityError with the offending data type in the message. Bedrock cannot fetch arbitrary web URLs for tool result files.

Source

Thrown at packages/amazon-bedrock/src/convert-to-amazon-bedrock-chat-messages.ts:400

                  continue;
                }
                let toolResultContent;

                const output = part.output;
                switch (output.type) {
                  case 'content': {
                    toolResultContent = await Promise.all(
                      output.value.map(async contentPart => {
                        switch (contentPart.type) {
                          case 'text':
                            return { text: contentPart.text };
                          case 'file': {
                            if (
                              contentPart.data.type !== 'data' &&
                              (contentPart.data.type !== 'url' ||
                                contentPart.data.url.protocol !== 's3:')
                            ) {
                              throw new UnsupportedFunctionalityError({
                                functionality: `tool result file data of type "${contentPart.data.type}"`,
                              });
                            }

                            const fullMediaType = resolveFullMediaType({
                              part: contentPart,
                            });

                            switch (getTopLevelMediaType(fullMediaType)) {
                              case 'image': {
                                return {
                                  image: {
                                    format:
                                      getAmazonBedrockImageFormat(
                                        fullMediaType,
                                      ),
                                    source: getAmazonBedrockMediaSource({
                                      data: contentPart.data,

View on GitHub (pinned to 69428b1f8b)

Solutions

Return the file as inline 'data' (base64/Uint8Array) from the tool with a supported media type.
Upload the file to S3 and return a file part with an s3:// URL.
Convert the file content to text and return it as a text tool result part instead.
Verify the tool result file part shape matches the AI SDK FilePart data union.

Example fix

// before (in tool result content)
{ type: 'file', mediaType: 'application/pdf', data: new URL('https://cdn.example.com/report.pdf') }
// after
{ type: 'file', mediaType: 'application/pdf', data: await downloadBytes('https://cdn.example.com/report.pdf'), filename: 'report.pdf' }

Defensive patterns

Strategy: validation

Validate before calling

function validateToolResultFile(part) {
  if (part.type !== 'file') return true;
  const ok = part.data.type === 'data' || (part.data.type === 'url' && part.data.url.protocol === 's3:');
  if (!ok) throw new Error(`Tool result file must be inline data or s3: URL, got: ${part.data.type}`);
  return true;
}

Type guard

function isInlineOrS3FileData(data) {
  return data.type === 'data' || (data.type === 'url' && data.url.protocol === 's3:');
}

Try / catch

try {
  return await generateText({ model, prompt });
} catch (error) {
  if (UnsupportedFunctionalityError.isInstance(error) && error.message.includes('tool result file data')) {
    console.error('Tool returned an unsupported file data type; inline the bytes or use s3://.');
  }
  throw error;
}

Prevention

Design tools to return file bytes inline or S3 URIs, never web URLs.
Add a unit test for every tool's output shape against the Bedrock converter.
Wrap tool execute() to normalize file parts before they reach the provider.

When it happens

Trigger: A tool returns a file part whose contentPart.data.type is neither 'data' nor 'url' with an s3: protocol — most commonly an https URL file inside a tool result.

Common situations: A tool fetches a document from the web and returns its URL as a file part; Bedrock requires the bytes (inline data) or an S3 location instead.

Related errors

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/e0540bef48712835. Report an issue: GitHub.