deepseek-ai/deepseek-harness · error

the declared media type is not PNG, JPEG, WebP, or GIF

Error message

the declared media type is not PNG, JPEG, WebP, or GIF

What it means

Error "the declared media type is not PNG, JPEG, WebP, or GIF" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/mcp/mcp-client/src/tools.ts:381

/** Whether an untrusted MCP content array contains a declared image block. */
function containsImage(content: JsonValue[]): boolean {
  return content.some(value => isRecord(value) && value.type === 'image')
}

/** Narrow one JSON value to a string-keyed object. */
function isRecord(value: JsonValue): value is { [key: string]: JsonValue } {
  return typeof value === 'object' && value !== null && !Array.isArray(value)
}

/** Narrow a declared MIME string to the durable image vocabulary. */
function isImageMediaType(value: string): value is ImageMediaType {
  return IMAGE_MEDIA_TYPES.includes(value as ImageMediaType)
}

/** Decode one untrusted MCP image block without accepting base64 aliases. */
function decodeImage(block: McpContentBlock): SaveImageAttachment {
  if (block.mimeType === undefined || !isImageMediaType(block.mimeType)) {
    throw new Error('the declared media type is not PNG, JPEG, WebP, or GIF')
  }
  if (block.data === undefined || !CANONICAL_BASE64.test(block.data)) {
    throw new Error('the image data is not canonical base64')
  }
  const data = Buffer.from(block.data, 'base64')
  if (data.toString('base64') !== block.data) {
    throw new Error('the image data is not canonical base64')
  }
  return { data, mediaType: block.mimeType }
}

/**
 * Resolve the active model route and durable store for an image-bearing result.
 * @param ctx - plugin context with optional services.
 * @param exec - exact tool execution whose agent supplies the latest route.
 * @returns the attachment store after exact positive image-capability proof.
 */
async function resolveImageAdmission(ctx: Context, exec: ToolExecution): Promise<AttachmentStore> {

View on GitHub (pinned to b150a551b8)

Solutions

1. Convert the image to PNG, JPEG, WebP, or GIF and fix the declared media type.

When it happens

Trigger: Thrown at packages/mcp/mcp-client/src/tools.ts:381 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of deepseek-ai/deepseek-harness@b150a551b8 (2026-08-24). Data as JSON: /api/errors/367b1fb4a6de402e. Report an issue: GitHub.