Portmux is a SaaS to custom build migration service for companies replacing off-the-shelf platforms with software they built themselves. Salesforce, NetSuite, Zendesk, HubSpot, Shopify, Jira, most systems with an API or a documented export. We move your data into your custom system without slowing down the build team.
Most data migration work assumes a known destination, Salesforce to HubSpot, NetSuite to QuickBooks, both ends documented, both schemas stable. Custom builds break that assumption. The destination is being written while you're trying to migrate into it. Schemas change. Endpoints rename. Validation rules emerge during UAT. We've run a number of migrations into custom-built platforms and learned how to land production data into a target that's still under construction. We work alongside your engineering team, version-pin the destination contract, and stage data as your build hardens, so you don't have to choose between shipping the new platform and migrating the old one.
All CRM contact, account, and company records from any SaaS source, deduplicated and reshaped to your custom domain model.
Orders, invoices, subscriptions, payments, refunds, and ledger entries from any source platform with full audit chain preserved.
Active and historical deals, stages, win/loss reasons, forecast categories, and stage-change timelines reshaped to your sales model.
Conversations, tickets, internal notes, attachments, SLAs, and CSAT data from Zendesk/Intercom/Freshdesk/etc. into your custom support model.
SKUs, variants, pricing, inventory, media, and category hierarchies from Shopify, NetSuite, BigCommerce, or any commerce/ERP source.
User records, password hashes (where exportable), SSO mappings, role assignments, and team membership reshaped to your custom auth model.
Every attachment from every source object, re-uploaded to your storage layer (S3, GCS, custom blob store) with associations preserved.
Login events, record changes, system actions, and audit trails carried forward so compliance and forensic queries still resolve after cutover.
Every custom object, custom field, picklist, and extension from the source SaaS, reshaped to your custom schema (or deliberately retired).
Sent email, transactional notification logs, message templates, and delivery records reshaped to your custom messaging schema.
Critical operational reports re-implemented as queries against your custom database, with the SQL or DSL handed off to your team.
Inventory of every active third-party integration on the source SaaS so your build team knows what your custom platform must replace or absorb.
We sit down with your build team and your business owners to inventory what's in the source SaaS, every object, every custom field, every active integration. In parallel, we read the destination contract: API spec, database schema, ORM models, whatever's authoritative. The deliverable is a "what survives, what dies" decision document. Most custom-build projects use this as the moment to retire 30–50% of legacy fields.
We write a versioned mapping doc, source schema → destination schema, with every transform decision in writing. Because the destination is moving, we version-pin the contract per phase. Your build team agrees: "between now and Phase 2 cutover, these endpoints don't break." We test against a destination preview environment your team controls, with seed data flowing through end-to-end before any production records move.
We dual-write to the custom platform during a 1–4 week rehearsal window so your team can validate UI flows, internal tools, and reports against real production data. On cutover, we run a final delta from the SaaS source, freeze writes, and switch traffic. You get a row-level reconciliation report: every record, accounted for. Migration code is handed to your engineers as a maintained repo, not a black box.
Every migration has its own gotchas. Here's what we plan for on this specific path.
Custom builds evolve. We solve this by version-pinning the destination contract per migration phase and structuring the migration in stages, so your build team isn't blocked from refactoring after a stage lands. We rebuild the mapping for the next phase against the new contract, not the old one.
We write the migration in your stack (Node, Python, Go, Rust) using your APIs and your conventions. The repo is owned by you, code-reviewed by your team, and runnable in your CI. When we leave, your engineers can re-run any migration script themselves. No vendor lock-in.
Most SaaS platforms won't export password hashes. We map users by email, generate one-time reset links, and orchestrate a password-reset email flow timed to cutover. SSO users (Okta, Google Workspace, Azure AD) are mapped via external ID claim and migrate without a reset.
If your custom build replaces a SaaS that's under SOC 2, HIPAA, or financial audit, the auditors will ask whether historical records are still queryable. We carry the audit log forward in a queryable format and document the data lineage from source object to destination row. The auditor sign-off pack is a deliverable, not an afterthought.
Single-system migrations like SaaS Platforms to Custom Build run as Track A engagements: one source, one destination, up to 1M records, 4–6 weeks. Final price depends on object volume, custom field count, and integrations, scoped on a 20-minute call before any commitment. See full pricing →
Tell us what's in the source, where it's going, SaaS or custom, and when you need to be live. You'll walk away with a scoped quote, a named engineer, and a go-live date.