---
summary: "Typed message channels with at-least-once delivery \u2014 scopes, queues,\
  \ routing rules, streams, and HITL specs inside ScaiGrid."
title: ScaiQueue
path: overview
status: published
---

ScaiQueue is the messaging primitive on top of ScaiGrid. You publish typed messages to queues, consumers claim and process them, and a built-in routing engine pushes matching messages between queues so you can build multi-stage pipelines without writing the plumbing yourself.

It is a ScaiGrid module: the same tenants, the same API keys, the same accounting and audit story as every other surface. There is no separate broker to deploy.

## When to use it

- You need agent-to-agent coordination — one agent publishes work, others claim and complete it.
- You need a human-in-the-loop step inside an otherwise automated pipeline.
- You want fan-out from one event to several consumers, each tracked independently.
- You want a built-in dead-letter queue, retry policy, and visibility-timeout enforcement, and you don't want to operate Redis Streams or RabbitMQ yourself.

If you just need a webhook to fire after one event, you don't need ScaiQueue — ScaiGrid's webhooks are simpler. Reach for ScaiQueue when you have stages, retries, ordering, or a HITL hand-off.

## What you get

- **Scopes and queues.** A scope is a namespace; queues live inside it. Each scope is auto-seeded with system queues (`_dead_letter`, `_events`, `_audit`, `_integrity`, `_corrections`).
- **Four ordering modes per queue.** FIFO, priority, deadline, or broadcast.
- **At-least-once delivery.** Visibility timeouts reclaim crashed consumers; retries up to `max_retries`; then dead-letter.
- **HITL specs.** Messages can carry a rendering spec describing what a reviewer sees and what they must decide.
- **Routing engine.** Rules with conditions and actions; first-match wins; circuit-breaker prevents loops.
- **Streams.** Chunked sequences (for long generations) with an assembler.
- **Subscriptions, ACLs, scope grants, cross-scope trust, message schemas, HITL pattern registry, GDPR erasure, audit log.**

## Two-minute mental model

You manage three nouns and a verb. A **scope** is a namespace. A **queue** is an ordered channel inside a scope. A **message** is a typed payload that travels through queues. The verb is **publish** — and on the consumer side, **claim, complete, fail, release, or extend**.

System agents (visibility-timeout enforcer, expiry enforcer, archiver, dead-letter monitor, priority-aging worker) do the housekeeping in the background. You don't run them; they're part of ScaiGrid.

## Where to go next

- [Quickstart](./quickstart) — scope, queue, publish, claim, complete in five minutes.
- [Architecture](./concepts/architecture) — how publish, claim, route, and reclaim fit together.
- [Topics, types, and HITL specs](./concepts/topics-and-types) — what makes a queue a typed channel.
- [Build a pipeline with routing](./tutorials/build-a-pipeline) — multi-stage flow with routing rules.
- [Add a human review step](./tutorials/human-review) — HITL messages end-to-end.
- [API reference](./reference/api) — every endpoint, request, response.

ScaiQueue's module ID inside ScaiGrid is `scaiqueue`; its API is mounted at `/v1/modules/scaiqueue/`.