Postscript SMS API
REST API for Postscript's SMS marketing platform, purpose-built for Shopify stores, enabling programmatic subscriber management, keyword management, and event-driven message triggers for e-commerce workflows.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
All traffic over TLS. API key authentication is straightforward but lacks granular scope control — a single key grants full account access. No per-key permission levels. Webhook events should be validated using signature verification if supported. PII (phone numbers, subscriber data) is present in all payloads.
⚡ Reliability
Best When
You operate a Shopify store already using Postscript for SMS marketing and need to integrate subscriber management or event triggers with custom apps, loyalty platforms, or external marketing tools.
Avoid When
Your store is not on Shopify, you need programmatic campaign creation and content management, or you require a full-featured messaging API beyond subscriber sync and event triggers.
Use Cases
- • Subscribe Shopify customers to Postscript SMS lists from a custom loyalty or rewards program sign-up flow
- • Sync subscriber opt-out events from Postscript webhooks to a master suppression list in an external CRM or ESP
- • Trigger automated SMS flows (e.g., abandoned cart, post-purchase follow-up) by firing custom events when Shopify order events occur
- • Query subscriber profiles to check opt-in status before sending a transactional message through another channel
- • Add or remove subscriber tags in Postscript to segment customers based on purchase history from Shopify order data
Not For
- • Non-Shopify e-commerce platforms — Postscript is deeply integrated with Shopify and most automation relies on Shopify data structures
- • High-volume B2B or enterprise SMS campaigns outside of e-commerce — the platform is optimized for DTC retail use cases
- • Two-way conversational SMS at scale — Postscript focuses on marketing campaigns, not full conversational messaging infrastructure
Interface
Authentication
API key authentication using a private API key passed as a Bearer token or in the X-Postscript-Api-Token header. API keys are generated in the Postscript dashboard and are account-scoped with no granular permission levels. Keys must be rotated manually. Postscript also supports Shopify OAuth for app integrations built on the Shopify App Store.
Pricing
Free tier available for small lists. Paid plans include message credits; overages are charged per message. Pricing is subscriber-count based. API access is included at all plan levels.
Agent Metadata
Known Gotchas
- ⚠ The API is tightly coupled to Shopify — subscriber records reference Shopify customer IDs and most automation flows depend on Shopify order or customer events, making it harder to use for non-Shopify integrations
- ⚠ Phone numbers must be in E.164 format; the API will reject non-standard formats but may return an unhelpful generic error rather than a format-specific message
- ⚠ Keyword and automation flows must be configured in the Postscript dashboard before they can be triggered via the API — agents cannot create or modify automation logic programmatically
- ⚠ Webhook delivery is not guaranteed to be in order — agents processing subscriber opt-out webhooks must handle potential out-of-order delivery and implement idempotent processing
- ⚠ The free tier has strict message volume limits that can be unexpectedly hit in testing; agents should implement rate-aware sending logic even in development to avoid hitting throttles
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Postscript SMS API.
Scores are editorial opinions as of 2026-03-06.