Returning pdf tool resources

[loeffel-io]

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Question Category

• Protocol Specification
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Your Question

Hey, i return the following from my tool

{
  "uri": "file:///Users/loeffel/Google Drive/My Drive/Gewerbe/Steuer/Steuer 2025/Februar/N26/google.com/6382285305241639-10.pdf",
  "mimeType": "application/pdf",
  "blob": "{base64content}"
}

claude desktop errors with Unsupported image type: application/pdf - whats wrong here?

[cpryland]

https://github.com/modelcontextprotocol/specification/blob/3ba3181c7779da74b24f0c083eb7055b6fc9d928/schema/2025-03-26/schema.ts#L692 shows that a tool call reponse must be text, and image, or audio.

Claude desktop just doesn't recognize the application/pdf mimeType. Other clients might.

I agree that there should be a standard way to send back a PDF from a tool.

Maybe provide text/markdown and embed that URL in the markdown result?

Though other Q&A's are not finding success with this approach.

[cpryland]

Also, what are you putting in blob:?