Use markdown action buttons

Use markdown action buttons to add inline, in-text affordances to a post — without using a message attachment. They’re useful when:

• A short message reads naturally with an “Approve” or “Reject” inline link.
• An integration wants to mix narrative text and action affordances in the same post body.
• The visual weight of a full message attachment isn’t warranted.

For attachment-style buttons and menus, see interactive messages.

How it works 

A markdown action has two parts:

1. A markdown link in the post body using the mmaction:// scheme, where the link host is the action ID:

   [Approve](mmaction://approve?ticket=ISS-101)
   

2. A matching entry in the post’s props.mm_blocks_actions registry that tells the server what to do when the link is clicked:

   {
     "mm_blocks_actions": {
       "approve": {
         "type": "external",
         "url": "https://integration.example.com/hook/approve",
         "context": {"project": "Demo Project"}
       }
     }
   }
   

The client renders the link as a button. Clicking it dispatches a request to the Mattermost server, which forwards the call to the integration’s url along with merged query parameters and any server-side context.

Example post payload 

The following payload posts a message with two markdown action buttons. The body markdown references action IDs defined in mm_blocks_actions.

{
  "channel_id": "qmd5oqtwoibz8cuzxzg5ekshgr",
  "message": "Ticket ISS-101 needs review: [Approve](mmaction://approve?ticket=ISS-101) [Reject](mmaction://reject?ticket=ISS-101)",
  "props": {
    "mm_blocks_actions": {
      "approve": {
        "type": "external",
        "url": "https://integration.example.com/hook/approve",
        "context": {"project": "Demo Project"}
      },
      "reject": {
        "type": "external",
        "url": "https://integration.example.com/hook/reject",
        "context": {"project": "Demo Project"}
      }
    }
  }
}

You can send this payload using the create post REST API, an incoming webhook, or from a plugin.

Submit using the REST API 

curl -X POST $MM_URL/api/v4/posts \
  -H "Authorization: Bearer $BOT_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "channel_id": "'$CHANNEL_ID'",
    "message": "Ticket ISS-101 needs review: [Approve](mmaction://approve?ticket=ISS-101) [Reject](mmaction://reject?ticket=ISS-101)",
    "props": {
      "mm_blocks_actions": {
        "approve": {
          "type": "external",
          "url": "https://integration.example.com/hook/approve",
          "context": {"project": "Demo Project"}
        },
        "reject": {
          "type": "external",
          "url": "https://integration.example.com/hook/reject",
          "context": {"project": "Demo Project"}
        }
      }
    }
  }'

Submit from a plugin 

A server-side plugin creates posts with markdown actions through the existing API.CreatePost / API.UpdatePost interfaces. The action url typically points at the plugin’s own HTTP handler.

post := &model.Post{
    ChannelId: channelID,
    UserId:    p.botID,
    Message: "Ticket ISS-101 needs review: " +
        "[Approve](mmaction://approve?ticket=ISS-101) " +
        "[Reject](mmaction://reject?ticket=ISS-101)",
    Props: model.StringInterface{
        "mm_blocks_actions": map[string]any{
            "approve": map[string]any{
                "type":    "external",
                "url":     fmt.Sprintf("/plugins/%s/inline_action/approve", manifest.Id),
                "context": map[string]any{"project": "Demo Project"},
            },
            "reject": map[string]any{
                "type":    "external",
                "url":     fmt.Sprintf("/plugins/%s/inline_action/reject", manifest.Id),
                "context": map[string]any{"project": "Demo Project"},
            },
        },
    },
}
_, err := p.API.CreatePost(post)

Plugin updates to mm_blocks_actions via UpdatePost are accepted only when the updated value passes validation. Removal of the mm_blocks_actions prop by non-integration sessions is restricted to prevent dropping or corrupting actions on posts owned by another integration.

Link syntax 

[<label>](mmaction://<action_id>?<query_string>)

<label>
The link text rendered as the button label.

<action_id>
The host portion of the URL. Must match a key in props.mm_blocks_actions. Must be alphanumeric ([A-Za-z0-9]+), matched case-sensitively.

<query_string> (optional)
key=value pairs that are forwarded with the dispatched action and merged into the target URL’s query string by the server. Link-supplied values override registry-supplied values on key conflict.

The mm_blocks_actions registry 

The mm_blocks_actions post prop is a map keyed by action ID. Each entry describes how the server should handle clicks on that action.

{
  "mm_blocks_actions": {
    "<action_id>": {
      "type": "<action_type>",
      "url": "...",
      "context": { ... },
      "query": { ... }
    }
  }
}

Action types 

Additional action types may be introduced as the broader Interactive Messages framework lands. Entries with an unknown type value are rejected at post-create time.

Click dispatch flow 

The diagram below describes the lifecycle of a single click on a markdown action button.

1. Integration creates a post with an mmaction://<id> link and a matching mm_blocks_actions[<id>] entry.
2. Mattermost server validates the post (mm_blocks_actions schema and limits) and stores it.
3. Client renders the link as a button. Clicking it dispatches POST /api/v4/posts/{post_id}/actions/{action_id} with the link’s query string in the request body.
4. Mattermost server looks up mm_blocks_actions[<id>], merges the registry’s static query with the request body’s query (request body wins on conflict), merges the result into the action URL’s query string, and POSTs the integration endpoint.
5. Integration responds with a standard post-action response.

Receiving action callbacks 

When a user clicks a markdown action button, the Mattermost server sends an HTTP POST request to the url configured in the matching mm_blocks_actions entry. The request body follows the same PostActionIntegrationRequest shape used by message attachment buttons — the integration responds with the same post-action response format.

Validation limits 

Posts that exceed any of the following limits are rejected at create or update time.

Error reference 

The following error IDs may be returned by the post-action and post-create APIs when processing markdown action requests.

Security considerations 

Markdown action buttons follow the same security model as message attachment actions:

• The action url is invoked server-to-server, never directly from the client.
• context values are server-only and are not exposed to the rendering client.
• Action IDs are validated as alphanumeric strings and matched case-sensitively.
• Action entries with malformed or unknown type values are rejected at post-create time and never reach the click-dispatch path.

See also 

• Interactive messages — message-attachment buttons and menus.
• Message attachments — broader message format reference.
• Incoming webhooks — submitting posts via webhooks.
• REST API: create post