mastra-ai/mastra · error

Unsupported part type: ${type}

Error message

Unsupported part type: ${type}

What it means

convertImageFilePart converts ImagePart/FilePart content to LanguageModelV2 file parts and switches only on part.type 'image' or 'file'. Any other part type reaching this function throws 'Unsupported part type: <type>', since this converter is only meant for image/file parts.

Source

Thrown at packages/core/src/agent/message-list/prompt/convert-file.ts:20

import type { LanguageModelV2FilePart, LanguageModelV2TextPart } from '@ai-sdk/provider-v5';
import { convertToDataContent, detectMediaType, imageMediaTypeSignatures } from '../../../stream/aisdk/v5/compat';

export function convertImageFilePart(
  part: ImagePart | FilePart,
  downloadedAssets?: Record<string, { mediaType: string | undefined; data: Uint8Array }>,
): LanguageModelV2TextPart | LanguageModelV2FilePart {
  let originalData: DataContent | URL;
  const type = part.type;
  switch (type) {
    case 'image':
      originalData = part.image;
      break;
    case 'file':
      originalData = part.data;

      break;
    default:
      throw new Error(`Unsupported part type: ${type}`);
  }

  const { data: convertedData, mediaType: convertedMediaType } = convertToDataContent(originalData);

  let mediaType: string | undefined = convertedMediaType ?? part.mediaType;
  let data: Uint8Array | string | URL = convertedData; // binary | base64 | url

  // If the content is a URL, we check if it was downloaded:
  if (data instanceof URL && downloadedAssets) {
    const downloadedFile = downloadedAssets[data.toString()];
    if (downloadedFile) {
      data = downloadedFile.data;
      mediaType ??= downloadedFile.mediaType;
    }
  }

  // Now that we have the normalized data either as a URL or a Uint8Array,
  // we can create the LanguageModelV2Part.

View on GitHub (pinned to 75dd419e61)

Solutions

1. Make sure only 'image' and 'file' parts are passed to this conversion path; route 'text' parts through the text-part converter.
2. Normalize custom part types to supported AI SDK part types before building the prompt.
3. Check for AI SDK major-version mismatches between your app and @mastra/core's pinned provider versions.
4. Log/inspect the offending part's type in the error message to find the producer.

Example fix

// before
parts.push({ type: 'audio', data } as any);
// after
parts.push({ type: 'file', data, mediaType: 'audio/mpeg' });

function onlyImageOrFile(parts: Array<{ type: string }>) {
  const bad = parts.filter(p => p.type !== 'image' && p.type !== 'file');
  if (bad.length) throw new Error(`Non image/file parts must not reach file conversion: ${bad.map(p => p.type).join(',')}`);
}

function isImageOrFilePart(p: { type: string }): p is ({ type: 'image'; image: unknown } | { type: 'file'; data: unknown }) {
  return p.type === 'image' || p.type === 'file';
}

try {
  converted = convertImageFilePart(part as any, downloadedAssets);
} catch (e) {
  if (e instanceof Error && e.message.startsWith('Unsupported part type:')) {
    console.error('Part routed to file converter with type:', (part as any).type);
    return routeToCorrectConverter(part); // e.g. text-part handler
  }
  throw e;
}

When it happens

Trigger: A content array containing a part whose type is not 'image' or 'file' (e.g. 'text' handled elsewhere but mis-routed, or a provider-specific/novel part type) reaching convertedContent → convertImageFilePart during prompt conversion.

Common situations: Custom prompt builders that push unknown part types into image/file conversion paths; version drift between AI SDK part types and the v2 provider parts; typos like 'image_part'.

Related errors

• runId is required when resumeData is provided
• Agent ${agentId} not found
• Messages must be an array of UIMessage objects
• Path must include :agentId to route to the correct agent or
• Agent ID is required

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/5826b48fd241c4c3. Report an issue: GitHub.