How One Team Replaced a 6-Figure HubSpot Agency with Claude Code

A mid-sized e-commerce company (~15 products across Shopify, Recharge, Digistore24, GoAffPro, and ads) needed to migrate from Zoho CRM, Zoho Desk, and KlickTipp to HubSpot Enterprise. Agency quotes ranged from 20k EUR (templated) to 80k EUR (mid-tier custom objects) — but none offered end-to-end custom middleware for sync/reconciliation. The team decided to build it themselves with Claude Code (desktop app, Opus 4.7, subscription plan).

What Was Built (in 4 months, ~30 sessions of 2-4h each)

• 6 Custom Objects + ~100 properties + associations
• 5 source-system integrations on self-hosted n8n: Shopify, Digistore24, Recharge, GoAffPro, Cart-Notifier — each with inbox pattern, idempotent upserts, reconciliation, backoff/retry, audit trail
• 1 custom Cloud Run service for inbox-polling at 15s cadence
• 10 Lifecycle stages + Funnel/Segment property layer
• Aggregator workflow that backfills 9 contact properties from sync-mirror objects (idempotent, Postgres cursor, cron-driven)
• KlickTipp migration: 202 tags audited, custom object for webinar registrations, consent governance
• Google Ads CAPI (11 conversion actions, enhanced conversions) + Meta CAPI (Pixel + server-side)
• 33 ADRs (architecture decisions, append-only, never deleted)

The author estimates the full deliverable would cost 120-180k EUR from an agency — and most can't deliver the custom middleware piece.

The Mental Shift: Claude Code as System-of-Record

Only ~20% of the repo is code. The other 80% is Markdown: architecture decisions, integration specs, runbooks, ADRs, naming conventions, consent governance. The repo becomes the single source of truth for how the business runs in HubSpot. When code is needed (Python helpers, backfill scripts, Cloud Run service), Claude writes it. For workflow logic, they use n8n — Claude builds/updates workflows via the n8n MCP server.

Repo as Memory Between Sessions

Claude Code sessions are stateless. The team treats this as a design constraint: state lives in files. Key practices:

• ADRs capture every architecture decision with reasoning and trade-offs — new sessions read them and don't re-debate
• Spec files per integration/area with a Status header — single source of truth for implementation state
• Slash commands (/implement, /verify, /new-task) enforce discipline — Definition-of-Done gate, drift checks, atomic status updates
• Cheatsheets for HubSpot operations (which work via API tools vs direct API calls vs UI clicks) and known bugs (HubSpot search index latency, Recharge enumeration-vs-bool, n8n auth races)