Courier

Courier is a multi-channel notification infrastructure platform providing a single REST API for sending notifications across email, push, SMS, Slack, in-app, and other channels. Rather than integrating with each notification channel separately, agents call Courier's send API with the notification content and recipient, and Courier routes to the appropriate channel based on user preferences and channel availability. This routing abstraction is particularly valuable for agents that need to reach users across their preferred channel without managing per-channel integration logic.

Authentication uses API keys for the REST API. Courier separates production and test environment keys. The key model is straightforward for server-side agent integration. Teams should monitor key usage and implement appropriate secrets management given that Courier keys authorize notification delivery to real users.

The API covers notification sends, templates, routing rules, user preferences, and delivery tracking. The send API accepts a recipient ID, template reference, and data — Courier handles channel selection, template rendering, and delivery. Agents can also subscribe users to channels, retrieve delivery status, and manage notification preferences through the API. The routing engine supports fallback logic (try email, fall back to SMS if undelivered).

Reliability is production-grade for a notification platform. Courier maintains the delivery infrastructure and handles provider fallback when individual notification providers experience issues. Delivery analytics enables agents to monitor notification delivery rates and detect systematic delivery failures.

Documentation is thorough and covers the send API, template system, and routing configuration clearly. The multi-channel routing documentation explains how to configure recipient channel preferences and fallback rules. Teams evaluating Courier versus Knock for multi-channel notification infrastructure should compare the routing rule expressiveness and template design capabilities.