---

name: upload-files description: > Turn local files or user attachments into public URLs by uploading them to the Gradio server, so tools that require http(s) URLs (htr_transcribe, the viewer) can reach them. Use when you have local images or ALTO/PAGE XML — an attachment or a file path — but a tool needs a URL.

Upload Files

Upload local files or user-provided attachments (images, XML, etc.) to the Gradio server so they become publicly accessible URLs. These URLs can then be passed to tools like htr_transcribe or the document viewer.

When to use

• User has attached images or XML files in the conversation
• User has local file paths that need to be accessible by a remote tool
• Any tool requires http/https URLs but you only have local data

If you already have http/https URLs (e.g. IIIF links, public image URLs), skip this skill entirely and pass them directly to the target tool.

Server URL

The upload target is the Gradio Space that backs the HTR MCP server:

https://riksarkivet-htr-demo.hf.space

Override with the HTR_SPACE_URL environment variable if set.

Upload workflow

Step 1: Save attachments to disk

If the user attached files in the conversation (not already on disk), save them first. Claude attachments are available as content in the conversation — write them to temporary files.

Step 2: Upload each file

For each file, POST to the Gradio upload endpoint:

curl -s -X POST "https://riksarkivet-htr-demo.hf.space/gradio_api/upload" \
  -F "files=@/path/to/filename.jpg"

Response is a JSON array of server paths:

["/tmp/gradio/abc123def/filename.jpg"]

Step 3: Construct public URLs

For each server path returned, construct the public URL:

https://riksarkivet-htr-demo.hf.space/gradio_api/file=/tmp/gradio/abc123def/filename.jpg

Pattern: {base_url}/gradio_api/file={server_path}

Step 4: Collect all URLs

Gather all constructed URLs before passing them to the target tool. Present the URLs to the user so they can verify the uploads succeeded.

Batch upload

You can upload multiple files in a single request:

curl -s -X POST "https://riksarkivet-htr-demo.hf.space/gradio_api/upload" \
  -F "files=@page1.jpg" \
  -F "files=@page2.jpg" \
  -F "files=@page3.jpg"

Response:

[
  "/tmp/gradio/abc123/page1.jpg",
  "/tmp/gradio/abc123/page2.jpg",
  "/tmp/gradio/abc123/page3.jpg"
]

Prefer batch upload over individual uploads when possible.

Supported file types

Type	Extensions	Use with
Images	.jpg, .jpeg, .png, .tif, .tiff	htr_transcribe, document viewer
ALTO XML	.xml	document viewer (text layer overlay)
PAGE XML	.xml	document viewer (text layer overlay)

After uploading

Once you have public URLs, pass them to the appropriate tool:

• HTR transcription: call htr_transcribe with image_urls=[...]
• Document viewer: call view_document with image_urls=[...] and optionally text_layer_urls=[...]

Error handling

• Connection error: the Gradio Space may be sleeping. Retry after 30 seconds.
• 413 Payload Too Large: file exceeds the server limit. Try uploading fewer files per request.
• Empty response: verify the file path is correct and the file exists.