@a24k/n8n-nodes-mattermost

An n8n community node for Mattermost that extends the built-in Mattermost node with support for file attachments and rich message attachments (Slack-compatible).

What's different from the built-in node

The built-in Mattermost node already supports plain posts, thread replies, and rich message attachments. The one gap this node fills is file upload.

Installation

In your n8n instance:

1. Go to Settings → Community Nodes
2. Click Install
3. Enter @a24k/n8n-nodes-mattermost
4. Click Install

The node appears as Mattermost @a24k in the node palette.

Requires n8n 1.x or later.
To use as an AI Agent tool, set N8N_COMMUNITY_PACKAGES_ALLOW_TOOL_USAGE=true on your n8n instance.

Credentials

This node reuses the built-in Mattermost API credential type (mattermostApi). No additional credential setup is required.

1. In n8n, go to Credentials → Add Credential → Mattermost API
2. Fill in:
   • Base URL — your Mattermost server URL (e.g. https://mattermost.example.com)
   • Access Token — a personal access token or bot token
   • Allow Unauthorized Certs — enable only if your server uses a self-signed certificate

Operation: Post Message

A single operation covers plain posts, file-attached posts, and rich attachment posts.

Parameters

File attachments

Enter binary property names separated by commas in the Files field (e.g. data, image, report). Each name must match a binary property on the current n8n item. Up to 10 files are supported; all files are uploaded before the post is created.

By default, files are uploaded in parallel (faster). To guarantee display order in Mattermost, enable Upload Files Sequentially under Advanced Options.

Example workflow:

HTTP Request (download file) → Mattermost @a24k (post with attachment)

In the Mattermost node, set Files to data (the default binary property name from HTTP Request).

To attach multiple files from a single item, set Files to e.g. data, screenshot, log.

Filename handling: if the binary data has no file extension, one is inferred from the MIME type (image/jpeg → .jpg, image/svg+xml → .svg, text/plain → .txt; other types use the MIME subtype as-is). application/octet-stream is left unchanged.

Rich attachments

Click Add Attachment to add one or more Slack-compatible message attachments.

Required field:

Optional fields:

Attachment Options (expand to reveal):

Fields (table-style columns within an attachment):

Advanced Options

Expand Advanced Options to access:

Output

On success:

{
  "post_id": "abc123",
  "channel_id": "xyz456",
  "message": "Hello!",
  "file_ids": ["fid1", "fid2"],
  "create_at": 1234567890000
}

When Thread Group Key is set, two additional fields are included:

{
  "post_id": "abc123",
  "channel_id": "xyz456",
  "message": "Hello!",
  "file_ids": [],
  "create_at": 1234567890000,
  "thread_group_key": "my-incident-123",
  "thread_root_post_id": null
}

thread_root_post_id is null for a new root post and the root post ID for thread replies.

Error handling

The node respects n8n's Continue on Fail setting.

If files were uploaded successfully but the post creation fails, the error output includes uploaded_file_ids so downstream nodes can handle orphaned files:

{
  "error": "...",
  "uploaded_file_ids": ["fid1", "fid2"]
}

Mattermost does not provide a public API to delete orphaned files, so cleanup must be handled at the infrastructure level.

License

MIT