[NEW PLUGIN] Upload Files to Slack

Showcase Plugins
1

Hi Bubblers,

As you may know, Bubble’s official Slack plugin doesn’t offer the option to post files. The only workaround to date is a custom three-step API connector call per file (get an upload URL, POST the bytes, finalize).

My dev partner and I built this plugin to hopefully save you a few hours of configuration, and so multi-file uploads land as one Slack message with one notification instead of a loop posting each file separately.

It is intended as a companion to the official Slack plugin.

Post any file to Slack. Up to 10 files at once, ~100 MB combined, with caption, in a specific channel or thread. Thread chaining for unbounded batches and private file hosting.

It has two actions:

  • Upload a Single File: post one file in a specific Slack channel (and, if needed, a specific thread).
  • Upload Multiple Files: post one Slack message with 2 to 10 attachments.

The result looks like that:
Screenshot of a Slack message with attachments

Full features list

  • Multi-file batching in one Slack message: up to 10 files appear as one grouped message under a single caption (takes ~1 WU per call regardless of file count).
  • Sequential Upload Mode for larger batches: handles batches up to ~100 MB combined instead of the 25 MB default. You get the same Slack-side result (one message with N attachments), one buffer at a time in memory.
  • Thread chaining for unbounded batches: each call returns the message_ts of the Slack message it posted. Pass it as the next call’s Thread Timestamp and the new batch lands as a thread reply. Chain as many calls as you need to post more than 10 files/100 MB in total.
  • Per-user private file hosting via DM channels: pass a direct-message channel ID (starts with D...) instead of a team channel ID, and the files are hosted in Slack but visible only to that user.
  • Filename auto-correction: the plugin trims whitespace, strips control characters and path separators, collapses repeated underscores, and truncates to 255 characters while preserving the extension. UTF-8 names with accents and emojis are kept as-is (every correction is logged).

What you can configure

Example of configuration

Option What it does
Caption A message above the file(s) using Slack’s mrkdwn formatting and emojis
Thread reply Pass a Thread Timestamp to post inside an existing thread
Title and alt text (per file) Override the displayed title; add screen-reader descriptions for accessibility (WCAG, ADA, Section 508, European Accessibility Act)
Sequential Upload Mode Toggle to handle batches up to ~100 MB combined
Filename auto-correction Plugin-side; you can also force space-to-underscore
Returned values file_id, file_permalink, message_ts, error_code, error_message, plus failed_filenames and success_count / failure_count for the multi-file action.

We recommend Bubble’s free Multi-File Uploader - Dropzone plugin if the files to slack come from your end users.

You can branch on error_code to recover gracefully in your workflow: retry on ratelimited, alert an admin on storage_limit_reached, drop the channel ID from a user record on channel_not_found, retry only the failed files on partial_success.

Reliability

  • Inputs pre-validated: Channel IDs are checked against the expected format before any network call. User tokens (xoxp-) and webhook URLs are rejected with a clear explanation. Bot tokens (xoxb-) and rotated tokens (xoxe.xoxb-) are both accepted.
  • Slack errors translated to human language: every Slack error code is explained in a paragraph that says what went wrong, what was received, and where in Slack or Bubble to go to fix it. Covers invalid_auth, missing_scope, channel_not_found, not_in_channel, is_archived, ratelimited, storage_limit_reached, thread_not_found, file_size_limit_exceeded, file_uploads_disabled, alt_txt_too_large, msg_too_long.
  • Combined-size pre-check: the plugin reads each file’s Content-Length before downloading and rejects oversized batches immediately.
  • Partial-success handling in Sequential mode: if one file fails, the others are still posted. The action returns error_code = partial_success, with the surviving files in file_ids and the failed names in failed_filenames.
  • Auto-retry on Slack rate limits: the plugin uses the official Slack SDK, which retries 429 responses honoring the Retry-After header. Multi-file batches count as one call, so grouping is a real rate-limit advantage.
  • Structured logs: every error is logged with the [Upload Files to Slack] prefix.

Feedback welcome

If you notice a bug, a weird interaction with another plugin, or there is a specific business case you would like the plugin to cover, please reach out. We react quickly!

1 Like