API integrations — connecting systems that don't talk

iPaaS for 60% of cases: faster (weeks instead of months), cheaper maintenance (drag-and-drop workflow), ready-made connectors for popular SaaS (Salesforce, HubSpot, Stripe, Slack). Price: 5,000–30,000 PLN/month. Custom (Java/Node/Python) when: (1) mass volume (>1M events/day where iPaaS becomes expensive per event), (2) unique business logic that iPaaS doesn't support, (3) legacy integrations (mainframe, AS/400, COBOL — no connector in iPaaS), (4) on-prem requirement (KNF, ISO 27001 — cloud iPaaS prohibited), (5) low-latency requirements (<10ms where iPaaS adds overhead), (6) full control over release cycle. We do both — we'll help you choose after a scope audit.

Yes, 10+ years of experience. KSeF (National e-Invoice System) — issuing and receiving XML invoices in the FA(3) schema, online/offline mode, handling corrections and prepayments. Mandatory from 2026. BIK (Credit Information Bureau) — credit history checks, BIK Kompletny, BIK Score, mTLS with certificate. KRS / CEIDG — company data lookup by NIP/REGON (KRS search). GUS / REGON — REGON number verification, statistical data. e-Doreczenia (Polish Post) — official document delivery. ePUAP — communication with public administration. JPK_VAT — audit file exports. BDO (waste register) — reporting, legal requirement. All with API documentation and vendor certificates.

Depends on complexity. Simple REST ↔ REST (e.g. WordPress → Mailchimp): 1–2 weeks. Mid-level with data mapping (e.g. e-commerce → Comarch ERP): 4–8 weeks. Complex with legacy (e.g. CRM → mainframe COBOL via MQ): 3–6 months. Portfolio of 5–10 integrations (e.g. for a bank, telco): 6–12 months with dedicated team. Every integration has milestones every 2 weeks with a demo. First working version (mock + happy path) — after 5–10 days. Production-ready (with error handling, retries, monitoring, security) — per complexity.

We've been doing this for 15 years — there's plenty of COBOL in Polish banks and insurance companies. Strategy: we don't rewrite mainframe from scratch (5+ years of risk, millions of USD). We expose a modern API in front of the mainframe — a REST/GraphQL gateway that translates to MQ/CICS/IMS. Patterns: (1) Strangler Fig — new features in modern stack, old ones stay. (2) Database View — new application reads from mainframe DB2 read-only via API. (3) Event-driven — mainframe publishes events to Kafka, modern systems consume. (4) Gradual migration — table by table, feature by feature, consistency monitoring. Experience with PZU, Aviva, SK banks.

Depends on scale. Single integration (REST, up to 5 endpoints): 490–990 PLN/month — security patches, monitoring, minor changes. Portfolio of 5–10 integrations: 1,990–3,990 PLN/month — same plus new connectors + onboarding new systems. Enterprise (50+ integrations, ESB, mainframe): 9,990–29,990 PLN/month — named team, SLA 99.95%, contractual penalties. Maintenance includes: monitoring (uptime, latency, errors), patching (CVE, dependencies), new external API versions (e.g. Salesforce v60 → v61), backup-recovery, on-call rotation. Dedicated team available for portfolios of 10+ integrations.

Most common path: (1) write to [email protected] with a description (which systems you're connecting, data flow direction, event volume, real-time or batch, compliance, deadline); (2) an API architect responds within 24 h with 5–7 questions; (3) 30-minute call with the architect; (4) Discovery workshop 1–2 wks with architecture selection (P2P / API Gateway / ESB / iPaaS); (5) proposal with OpenAPI spec and specific price within 48–72 h; (6) NDA + MSA + SOW and start. Pre-Discovery audit (free, 2 days) for architecture selection — we'll advise custom vs iPaaS, REST vs SOAP, on-prem vs cloud.