linshenkx/prompt-optimizer · error · EvaluationValidationError

${label} #${index + 1} must provide either assetId or b64.

Error message

${label} #${index + 1} must provide either assetId or b64.

What it means

Each media item in an evaluation must reference its image by exactly one mechanism: either a stored assetId or inline base64 (b64). This error fires during validation when an item provides neither — both fields are absent or whitespace — so the service has no image payload to use.

Source

Thrown at packages/core/src/services/evaluation/service.ts:1679

  private hasMediaPayload(mediaItem: EvaluationMediaItem | null | undefined): boolean {
    const assetId = mediaItem?.assetId?.trim() || '';
    const b64 = mediaItem?.b64?.trim() || '';
    return !!assetId || !!b64;
  }

  private validateMediaItems(mediaItems: EvaluationMediaItem[], label: string): void {
    mediaItems.forEach((item, index) => {
      const itemLabel = item?.label?.trim() || '';
      const assetId = item?.assetId?.trim() || '';
      const b64 = item?.b64?.trim() || '';

      if (!itemLabel) {
        throw new EvaluationValidationError(`${label} #${index + 1} label must not be empty.`);
      }

      if (!assetId && !b64) {
        throw new EvaluationValidationError(
          `${label} #${index + 1} must provide either assetId or b64.`
        );
      }

      if (assetId && b64) {
        throw new EvaluationValidationError(
          `${label} #${index + 1} must not provide both assetId and b64.`
        );
      }
    });
  }

  private validateContentBlock(
    block: EvaluationContentBlock | undefined,
    label: string
  ): void {
    if (!block) {
      throw new EvaluationValidationError(`${label} must not be empty.`);

View on GitHub (pinned to 3e677b1d9f)

Solutions

1. Add either a valid assetId (from image storage) or a base64 data string to the offending media item
2. If the image is missing entirely, remove the media item rather than submitting an empty shell
3. Validate media arrays client-side before calling the evaluation API

Example fix

// before
media: [{ label: 'prompt image' }]

// after
media: [{ label: 'prompt image', b64: base64String }]

function validateMediaSources(media: { assetId?: string; b64?: string }[]): void {
  media.forEach((item, i) => {
    const hasAsset = !!item?.assetId?.trim();
    const hasB64 = !!item?.b64?.trim();
    if (!hasAsset && !hasB64) throw new Error(`media[${i}] needs assetId or b64`);
    if (hasAsset && hasB64) throw new Error(`media[${i}] must not set both assetId and b64`);
  });
}

const hasImageSource = (m: { assetId?: string; b64?: string } | undefined): boolean =>
  !!(m?.assetId?.trim() ^ m?.b64?.trim()); // exactly one set

try {
  await evaluationService.create(request);
} catch (err) {
  if (err instanceof EvaluationValidationError && /either assetId or b64/.test(err.message)) {
    fixMediaItemFromMessage(err.message); // attach assetId or b64 to the named item
  } else throw err;
}

When it happens

Trigger: A media item in a content block's media array with neither assetId nor b64 (both missing, empty, or whitespace). The message includes the block label and 1-based item index.

Common situations: Building media items from user input where both fields were left blank; a form or importer that drops the image field when upload fails; refactoring code from b64 to assetId and accidentally removing both.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• ${label} #${index + 1} label must not be empty.
• ${label} #${index + 1} must not provide both assetId and b64
• ${label} must not be empty.
• Result evaluation snapshot testCaseId must match testCase.id
• Image result evaluation requires at least one output image e

AI-assisted analysis of linshenkx/prompt-optimizer@3e677b1d9f (2026-08-27). Data as JSON: /api/errors/8d2dd53691eb840c. Report an issue: GitHub.