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Why “Exoskeleton”?

Sendy is a solid, proven email marketing tool — 50K+ licenses sold, reliable SES integration, simple interface. But its API is 7 legacy POST endpoints. No webhooks. No analytics API. No CLI. No AI. No health monitoring. SendyKit doesn’t replace Sendy. It wraps around it. Like an exoskeleton augments a human body — same body, dramatically expanded capabilities:
Sendy (the body)SendyKit (the exoskeleton)
7 POST endpoints125 REST endpoints
No CLI240+ commands
No webhooksHMAC-signed webhook delivery
No analytics APIFull intelligence engine
No health checks68 automated diagnostics
No audit trailAutomatic mutation logging
SES onlyAny SMTP provider
No AISubject lines, email gen, insights
No visual editorGrapeJS drag-and-drop
PayPal only (bypassable)Stripe + cryptographic payment tokens

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How It Works Technically

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Database Layer

SendyKit reads Sendy’s existing tables (campaigns, subscribers, lists, links, login, apps) via read-only queries. It never writes to Sendy’s core tables. SendyKit creates its own tables with the sendykit_ prefix:
  • sendykit_migrations — migration tracking
  • sendykit_feature_flags — runtime feature toggles
  • sendykit_webhooks — webhook endpoint configuration
  • sendykit_proxy_settings — proxy and transport settings
  • sendykit_analytics_events — enriched event tracking
  • sendykit_doctor_reports — health check results
  • sendykit_audit_log — mutation audit trail
  • sendykit_tenants — multi-tenant SaaS
  • sendykit_payments — payment verification

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Proxy Layer

The Sendy admin UI is served through SendyKit’s reverse proxy. This allows:
  • CSS injection (dark mode, mobile responsive, design system)
  • Sidebar navigation (SendyKit pages appear in Sendy’s nav)
  • Payment interception (Stripe replaces PayPal)
  • Brand switching (unified dropdown)
Sendy’s PHP code is never modified. The proxy intercepts HTTP responses and injects CSS/JS before serving to the browser.

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Safe Migrations

Every database migration is:
  1. Versioned — v001_foundation.sql through v007_billing.sql
  2. Non-destructive — Never ALTERs Sendy tables. Only CREATEs sendykit_* tables.
  3. Tracked — sendykit_migrations table records which migrations have run
  4. Idempotent — Safe to run multiple times
  5. Reversible — Can DROP all sendykit_* tables to fully uninstall

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Fail-Safe Design

If SendyKit stops running:
  • Sendy continues working exactly as before
  • All campaigns continue sending
  • All subscriber management continues
  • The only things lost are SendyKit-specific features (API, CLI, admin pages)
This is the key advantage of the exoskeleton model: zero risk to the existing system.