Ably Realtime API
Provides globally distributed pub/sub messaging infrastructure with channels, presence tracking, and guaranteed message ordering for real-time applications.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Capability-scoped tokens are a strong pattern. API keys should be server-side only; short-lived token requests are the correct client pattern. Ably supports mutual TLS on enterprise plans.
⚡ Reliability
Best When
You need globally low-latency pub/sub with presence, guaranteed ordering, and connection state recovery for real-time agent or user coordination.
Avoid When
You need messages to persist indefinitely and be replayed on demand, or require synchronous request/response semantics.
Use Cases
- • Broadcasting agent status updates and task progress to subscribed clients via channels
- • Coordinating multi-agent pipelines where agents publish events to trigger downstream agents
- • Maintaining live presence state for which agents or users are currently active in a session
- • Streaming LLM output tokens from backend agents to frontend clients in real time
- • Implementing agent-to-agent command and control messaging with delivery guarantees
Not For
- • Durable persistent storage — messages are transient and not queryable after delivery
- • Request/response RPC patterns — Ably is push-based and not designed for synchronous calls
- • Replacing a task queue or job broker — no built-in retry, scheduling, or dead-letter queues
Interface
Authentication
API keys support capability-based scoping per channel and operation. Token requests allow short-lived delegated credentials, which is the recommended pattern for client-side agents.
Pricing
Pricing scales on messages and peak connections. Reactor integrations (webhooks, serverless) count as messages.
Agent Metadata
Known Gotchas
- ⚠ Connection state machine has multiple states (connecting, connected, disconnected, suspended, closed) — agents must handle all states, not just connected/disconnected
- ⚠ Token expiry mid-session will silently drop messages unless the agent implements an authCallback to refresh tokens
- ⚠ Channel reattachment after network interruption is automatic but messages published during disconnect may be missed unless the agent uses rewind or channel history
- ⚠ Presence enter/leave events can fire multiple times during reconnects, causing agents to double-count active members
- ⚠ REST publish and Realtime SDK publish have different rate limit buckets — mixing both in one agent can cause unexpected throttling
Alternatives
Full Evaluation Report
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Scores are editorial opinions as of 2026-03-07.