File input

A file picker for collecting uploads in a modal, up to a configurable file count and type list.

file_input lets someone attach one or more files to a form. It’s an input-block-only element, and Slack restricts it further than most: it’s only supported in modals, not in messages or Home tabs.

Fields

Examples

Restricted to specific file types

The preview above limits uploads to pdf and png files via filetypes, and to 3 files via max_files. The native file picker only offers matching files, but treat this as a convenience for the person filling out the form. Validate the uploaded file types yourself when you handle the submission.

Any file type, single upload

Without filetypes, any file is accepted. max_files: 1 still shows the same singular “Upload File” button; Slack doesn’t change its label based on the limit.

Interactivity

Picking files calls onAction with the picked files’ metadata under files:

{
  "type": "file_input",
  "action_id": "files",
  "block_id": "attachments",
  "action_ts": "1706000000.000100",
  "files": [{ "id": "F1706000000000", "name": "report.pdf", "filetype": "pdf", "size": 48213 }]
}

Reading the value

Picking files writes the same list to state.values as { type, files }:

{
  "attachments": {
    "files": {
      "type": "file_input",
      "files": [{ "id": "F1706000000000", "name": "report.pdf", "filetype": "pdf", "size": 48213 }]
    }
  }
}

Related