Expo Notifications

Expo Push Notifications abstracts Apple APNs and Google FCM into a single REST endpoint — agents POST to exp.host/--/api/v2/push/send with an Expo push token and message payload, and Expo routes delivery to the correct platform. Works only with React Native/Expo apps that use the expo-notifications SDK (which handles token registration). For agents, this dramatically simplifies mobile push compared to direct APNs/FCM integration: no per-platform credentials needed, no platform-specific payload formatting, and a single delivery endpoint. Free for up to 1M messages/month. Receipts confirm per-device delivery status. Confidence is docs-derived.

Development: no authentication required (open endpoint, rate-limited by IP). Production: Expo Access Token as Authorization: Bearer for higher rate limits and analytics. Access tokens from expo.dev/accounts/{username}/settings/access-tokens. Expo push tokens (ExponentPushToken[xxx]) obtained from the client app via expo-notifications SDK — tokens are user/device identifiers, not auth credentials. No per-message signing required. HTTPS enforced.

docs.expo.dev/push-notifications provides a complete guide: push token registration (client SDK), sending pushes (server REST API), handling receipts, and error handling reference. Server-side sending examples in Node.js, Python, and Go. expo-server-sdk packages available (npm: expo-server-sdk; pypi: exponent_server_sdk). Getting started requires an Expo account (free). Client app must use expo-notifications SDK for token registration. Delivery is iOS/Android only (no web push). Community support via Expo Discord and GitHub Discussions.

REST API at exp.host/--/api/v2. Resources: push/send, push/getReceipts. POST /push/send sends notifications (single or batch up to 100). Request body: array of push message objects [{to: 'ExponentPushToken[xxx]', title, body, data, sound, badge, ...}]. Response: array of ticket objects ({status: 'ok'|'error', id: receiptId}). POST /push/getReceipts checks delivery status for receipt IDs (call 15-30 min after send). Receipt status: 'ok' (delivered to platform), 'error' (DeviceNotRegistered, MessageTooBig, etc.). JSON Content-Type required. Batch sends recommended for throughput.

Ticket errors: DeviceNotRegistered (uninstalled app — token should be removed), MessageRateExceeded (too fast to one device), MessageTooBig (>4KB payload). Receipt errors (checked async): same error types with permanent/transient classification. HTTP 400 for malformed request, 429 for rate limit (with Retry-After). Expo handles APNs/FCM quota; agents are isolated from platform-level rate limits. Free tier: up to 1M notifications/month. Paid tier: higher volume + analytics. Expo service status at status.expo.dev. Delivery is best-effort (no retry guarantee for permanent errors).