UI extensions (HubSpot's modern app cards, formerly CRM cards) are bespoke React interfaces that live inside HubSpot records, the help desk and full-screen app pages. We are the software engineering firm for HubSpot customers, so we build them properly with the @hubspot/ui-extensions SDK, serverless functions and real data integration.
When HubSpot's stock UI cannot show the data your team needs, or cannot trigger the action they want, a custom card closes the gap without sending people off into a second system. Here is where they earn their place.
Pull live data from an ERP, billing platform, support desk or logistics system and render it on a contact, company, deal or ticket. Your reps see the full picture on the HubSpot record itself, with no tab-switching, using hubspot.fetch() or serverless functions to read your back-end in real time.
Add buttons that create a related record, push an update to an external system, add a note, send an email or kick off a downstream workflow. We wire the CrmActionButton and serverless logic so a single click on the record does the work that used to take five screens.
Display aggregated metrics such as account health, usage trends, renewal risk or lifetime value as charts, statistics and status tags. We compute the values server-side and present them with the SDK's BarChart, LineChart, Statistics and StatusTag components so the numbers are always current.
Embed internal tooling directly in the record: guided multi-step processes, approval flows, or association management that goes beyond HubSpot's default UI. Forms, inputs, modals and panels from the SDK let your team complete structured work without leaving the CRM.
Add app cards to the Service Hub help desk sidebar so agents see customer context, entitlements or system status alongside the ticket. This surface needs Service Hub Pro or above, and we scope the data and actions around the way your agents actually work.
Build full-screen app pages for operational dashboards, guided workflows or admin tooling, plus settings pages for managing credentials and toggles. These give power users a rich, purpose-built workspace inside HubSpot rather than a bolt-on external app.
We build UI extensions inside HubSpot developer projects with the official SDK, the same engineering discipline we apply to every custom build.
We map exactly which records and surfaces the card lives on (crm.record.tab, crm.record.sidebar, crm.preview, helpdesk.sidebar, home or settings), what data it reads, and which actions it performs. We confirm tier eligibility up front, because building UI extensions requires a HubSpot Enterprise subscription and Super Admin access, and help desk sidebar cards specifically need Service Hub Pro or above.
We build the interface in React and TypeScript using @hubspot/ui-extensions and @hubspot/ui-extensions/crm, registered through the hubspot.extend() entry point and configured in the *-hsmeta.json metadata file. We use the SDK's component library (tables, forms, charts, tiles, modals and CRM data components) so the card looks native and behaves predictably.
We connect external systems with serverless functions and hubspot.fetch(), designing around the real platform limits: the 15 second default timeout (120 seconds maximum), 1 MB payload cap, and 20 concurrent requests per app. Where Sensitive Data scopes are in play we architect accordingly, since those apps cannot use hubspot.fetch(), which keeps sensitive data from being sent to external services.
We iterate against a local dev server with hot reload (hs project dev), upload through the HubSpot CLI and validate on real records before go-live. If you are still running legacy JSON-based CRM cards, we migrate them to the App Cards format ahead of the 31 October 2026 deadline so nothing breaks.
We package the extension cleanly and, where it suits you, host the supporting services on Railway as a productised, customisable solution you can run yourself. You get documented, maintainable code, not a black box, so your team is never locked in.
Everything you need to know about our services
Our projects start from £8,000. That figure is indicative rather than a fixed quote: the real cost is driven by scope (how many cards and surfaces), the number and complexity of external integrations, data volume and the back-end logic involved. A focused single card sits near the lower end, while integration-heavy or multi-card builds run higher. We work fixed-price wherever we can once scope is clear, and we back delivery with our guarantee: delivered on time, or you get 20% back.
Yes. Building and using private app cards requires a HubSpot Enterprise subscription. Since 14 November 2024 any Enterprise-tier hub qualifies, where previously it was limited to Sales Hub or Service Hub Enterprise. Customising the Service Hub help desk sidebar specifically requires Service Hub Pro or above. You also need Super Admin permission on the account to build. Importantly, end users do not need a paid seat to view or use a deployed extension once it is live.
This is genuine software engineering and it is what we do. SpotDev is a UK HubSpot Diamond Partner and HubSpot Custom Integration Accredited, with an in-house engineering team that writes real React and serverless code rather than relying on no-code glue. Our own website theme is built with React UI work and HubSpot serverless functions, so the capability is proven in production. We follow a Default to Build approach: when the platform alone is not enough, we build the software around it.
No. UI extensions are scoped to the surfaces you choose and run within HubSpot's developer project and private app model, so they sit alongside your existing CRM rather than altering it. We design them to read and write data deliberately through the SDK and serverless functions, and we test against real records before go-live so you can be confident nothing else is disturbed.
Yes. The legacy JSON-based CRM cards are being retired and must be migrated to the modern App Cards format by 31 October 2026. We handle that migration for you, rebuilding the card on the React-based @hubspot/ui-extensions SDK so it keeps working and gains the richer component library and action support that the modern platform offers.
A great deal. The SDK can read CRM properties and associations, call external services with hubspot.fetch(), and run back-end logic in serverless functions, with a context object that exposes the current user, account and record. Built-in actions include adding notes, opening an email composer, creating records and triggering external workflows, plus UI actions like alerts, copy-to-clipboard and opening modals or panels. The main constraints to design around are the fetch timeout and payload limits, and the rule that sidebar cards cannot use CRM data components, all of which we account for in the build.
Decision-stage guides on planning, costing and migrating to HubSpot UI extensions.
HubSpot is sunsetting legacy CRM cards on 31 October 2026. What the migration involves and why to move early.
Three commonly-confused ways to extend HubSpot, and when to use which.
What drives the price of a UI extension build, and how to scope it.
How to decide between an off-the-shelf app and a bespoke build.
