Onesignal

REST API at onesignal.com/api/v1/. Notification sending: POST /notifications with target (segments, filters, specific player IDs, external user IDs), content (headings, contents, url), and channel-specific options. The targeting system is flexible: segment-based (Active Users, Inactive Users, custom), filter-based (tag, language, location, app version), or direct (player_id or external_user_id lists). Player management: GET/PUT /players for device/user management. Tags: key-value pairs on players for custom segmentation. Template management for reusable notification designs. Outcomes API tracks notification-attributed events. The API handles platform-specific delivery details (APNs payload format, FCM data messages) transparently — agents send one request, OneSignal handles per-platform delivery.

API errors return JSON with errors array. Notification creation returns an id for tracking delivery status. Delivery outcomes (sent, clicked, received) are available via the View Notification endpoint. Invalid player IDs are reported in the response. Rate limits: generous for notification sending (varies by plan). Large audience notifications are queued and delivered asynchronously — delivery can take minutes for millions of devices. Push notification delivery is best-effort (platform limitation — APNs/FCM don't guarantee delivery). Invalid tokens are automatically cleaned up. The main reliability consideration: push notification delivery depends on device connectivity, OS notification settings, and platform-specific behavior — agents should not treat push as guaranteed delivery.

OneSignal is the most widely adopted push notification platform, supporting iOS, Android, Web, email, SMS, and in-app messages from a single API. For agents, the primary value is multi-channel notification delivery: send a push notification, email, or SMS to specific users or segments via one API call. The free tier includes unlimited push notifications — rare for notification platforms. Audience management with tags and segments enables targeted messaging. Journeys automate multi-step notification sequences. A/B testing optimizes notification content. For agents building user engagement — onboarding sequences, transactional notifications, re-engagement campaigns — OneSignal provides comprehensive multi-channel delivery. The main consideration: push notification setup requires platform-specific configuration (APNs for iOS, FCM for Android, VAPID for Web).

REST API key (App Auth Key) provides full API access per OneSignal app. User Auth Key provides account-level access across apps. REST API key is passed via Authorization: Basic header. The key grants broad access — no fine-grained scoping. Separate keys for different apps provide app-level isolation. No OAuth for third-party integrations. Keys don't expire. For agents, the per-app key model means creating separate OneSignal apps for different environments provides clean credential isolation. The User Auth Key should be used sparingly — it accesses all apps in the account. Client-side SDK keys are separate from REST API keys.

Documentation at documentation.onesignal.com is comprehensive, covering API reference, SDK setup guides (iOS, Android, Web, React Native, Flutter, Unity), and platform configuration (APNs, FCM, VAPID). The API reference covers all endpoints with parameters and examples. Platform setup guides walk through certificate/key configuration for each push platform. The documentation's main challenge: initial setup requires platform-specific knowledge (Apple developer certificates, Firebase project configuration) that's outside OneSignal's control. Community resources include a knowledge base and support forum. For agents, the REST API reference and the 'Send a Notification' guide are the starting points. SDK documentation varies in quality by platform.