Protocol¶

SlackMQ's protocol is built entirely on Slack channels and emoji reactions. No custom API, no webhooks — just channels, messages, and emoji.

Topology Commands¶

All topology is managed via /smq slash commands:

/smq topic #channel          — Register a channel as a topic
/smq subscribe #queue to #topic — Subscribe a queue to a topic
/smq dlq #dlq for #queue    — Assign a dead-letter queue
/smq unsubscribe #queue from #topic — Remove a subscription
/smq untopic #channel        — Stop watching a topic
/smq status                  — Show current topology

Emoji Protocol¶

The delivery lifecycle is driven entirely by emoji reactions:

Emoji	Meaning	Applied By
:package:	Fan-out marker — message has been copied to subscriber queues	Broker
:eyes:	Claim — a consumer is looking at this message	Consumer
:lock:	Locked — broker confirms the claim, consumer may proceed	Broker
:thumbsup:	ACK — message successfully processed	Consumer
:thumbsdown:	NACK — consumer cannot process this message	Consumer
:repeat:	Redelivery — message is being retried	Broker
:skull:	Dead letter — message exhausted all retry attempts	Broker

Delivery Lifecycle¶

1. Publisher posts message to topic channel
2. Broker detects message, adds :package:, copies to subscriber queues
3. Consumer adds :eyes: to claim a queue message
4. Broker adds :lock: to confirm the claim
5. Consumer processes the message
6. Consumer adds :thumbsup: (ACK) or :thumbsdown: (NACK)
7. On NACK: broker adds :repeat: and redelivers (up to max_attempts)
8. On final failure: broker adds :skull: and routes to DLQ (if configured)

Delivery Guarantees¶

At-least-once: Default mode. Messages may be delivered more than once if a consumer crashes before ACKing.
Exactly-once: Achievable when the broker and consumers share the same bot token (the broker can detect its own fan-out messages and skip re-processing).

Message Metadata¶

The broker tracks metadata per delivery:

Source topic — which topic the message originated from
Attempt count — current delivery attempt number (starts at 1)
Original timestamp — the Slack message timestamp from the topic