HubSpot custom development, by senior engineers who ship.
When standard HubSpot doesn't cover the use case, custom code does. UI extensions, serverless functions, custom CMS themes, programmable workflow actions, AI agents. Senior engineers, code committed to your repo, version-controlled, fully documented, supported in production.
Custom code that actually ships.
Four real custom development engagements. Each card links to the full case study with the technical scope and business outcome.
3 AI agents shipped to production
Lead scoring, support triage, outbound personalization. Each agent is a serverless function with HubSpot UI extension.
Custom UI extension on every deal
Promptly ships sales context (product usage, support tickets, contract terms) to the deal record via a custom UI extension.
12 programmable workflows in production
Anchor's RevOps motion uses 12 programmable workflows in TypeScript for routing, dedup, enrichment, and escalation.
Custom CMS theme for product catalog
Hunter Pumps' product catalog runs on a custom Content Hub theme with structured data tied to inventory.
When custom code fits, and when it truly doesn't.
We've shipped 300+ custom features. We've also told customers no when standard HubSpot would do the job. Below is the honest read.
Right fit when
- Standard HubSpot doesn't cover the use case and an off-the-shelf integration doesn't either.
- You need code committed to your repo, version-controlled, and supportable by your team.
- Your engineering team can't or won't take this on themselves and you need senior partner engineers.
- You require dedicated production monitoring and on-call coverage for the custom code.
- Build-time is faster than waiting for HubSpot to ship the feature you need.
Wrong fit when
- Standard HubSpot covers 80% of the need and you're trying to bridge the last 20% with custom code.
- You're a sub-10-person startup who'd be better served by a no-code workaround for now.
- Your team doesn't have engineering capacity to maintain custom code post-handoff.
- The use case will change every quarter and a hardcoded custom feature will be obsolete in 6 months.
What we actually build.
Custom development at HubSpot covers four primary surfaces. Below is the structure.
Custom React in HubSpot UI
Custom UI extensions inside contact, deal, and ticket records. React components fetching data from your APIs in real time. Used for context surfacing, in-record automation, lightweight admin tools.
Programmable workflows + serverless
Programmable workflow actions in TypeScript or Python. Serverless functions for heavy lifting. AI-extension actions wrapping LLM calls with proper guardrails. All version-controlled in your repo.
Custom Content Hub themes
Custom Content Hub themes for product catalogs, resource libraries, multi-language sites, and lifecycle-aware templates. HubL + JSON modules. Brand-aligned. Mobile-first.
From kickoff to production-grade feature.
Six steps. Same approach used on every custom feature above. Built to ship reliable code your team can own.
Discovery
Two sessions with engineering and business stakeholders. Use case clarity, edge cases, success metrics, build vs buy analysis. Output: technical specification with effort estimate.
Architecture
Component design, API contracts, error handling strategy, monitoring plan, rollback strategy. Designed before coded. You sign off.
Build
Senior engineers write the code in your repo or our handoff repo. Tests included. Code review against your team's standards. Storybook for UI components where applicable.
Deploy
Stage in HubSpot sandbox plus a non-prod environment. End-to-end test runs. Production rollout in stages with feature flags. Monitoring wired before flag flip.
Monitor
Slack alerts wired. Quality monitoring on critical surfaces. Daily reconciliation reports for high-volume code paths. Escalation paths documented.
Hand off
Code in your repo. Documentation covering architecture, error paths, monitoring setup, common-failure runbook. Your team owns it. Optional retainer for ongoing tuning and net-new builds.
Inside a custom development engagement.
Real deliverables, not capability bullets. Below is the typical scope on a custom feature build, fixed-fee from $14,500.
Architecture
- ·Discovery sessions with engineering + business stakeholders
- ·Technical specification document
- ·API contracts and component design
- ·Error handling and monitoring plan
- ·Rollback strategy with feature-flag plan
- ·Sign-off gate before coding begins
Build
- ·UI extensions, programmable workflows, serverless functions, or CMS theme
- ·Unit tests covering happy path and known error cases
- ·Integration tests against sandbox + non-prod source
- ·Code review against your team's standards
- ·Documentation in your repo
- ·Deploy script and CI configuration
Production
- ·Staged rollout with feature flags
- ·Slack alerts wired to your incident channel
- ·Quality monitoring on critical surfaces
- ·Production runbook with common-failure paths
- ·30-day post-launch warranty
Hand off
- ·Code committed to your repo with full documentation
- ·Architecture document (PDF + editable)
- ·Operational runbook for the feature
- ·Suggested optimization roadmap for months 4-12
Per-feature. Complexity-aware.
Light custom features (single UI extension or one programmable workflow): $14,500. Standard (multi-component, real-time, monitoring): $24,500. Enterprise (AI agents, custom CMS theme, multi-system): $48,000+. Ongoing maintenance retainers from $2,500 monthly.
Things people ask.
What languages do you write in?+
TypeScript or Python primarily. UI extensions are React (TypeScript). Programmable workflows are JavaScript or Python. Serverless functions are TypeScript on AWS Lambda or Vercel. CMS themes are HubL + JSON modules + Tailwind CSS.
Where does the code live?+
Your repo if you want it there. Our handoff repo if you don't have one ready. Either way, version-controlled, peer-reviewed, with CI configured. Your team owns the code after handoff.
Do you build AI agents?+
Yes. We've shipped 15+ AI agents to HubSpot production: lead scoring, support triage, outbound personalization, sales call summarization, support ticket auto-resolution. Each agent is a serverless function calling LLM APIs with proper guardrails and monitoring.
Can you build UI extensions?+
Yes. UI extensions are React components rendered inside HubSpot contact, deal, ticket, and custom-object records. Common use cases: surfacing product usage data, displaying support context, embedding internal-tool actions. We've shipped 50+ to production.
Do you support and monitor the code after launch?+
Yes via a maintenance retainer ($2.5K to $10K monthly depending on scope). Without a retainer, the build includes a 30-day post-launch warranty: we fix any bugs we shipped at no extra cost. After 30 days, your team owns it.
Can you work alongside our internal engineers?+
Yes. About 30% of our custom builds pair us with an internal engineering team. We typically take the HubSpot-specific surface area; they own the broader system. Clean code review and handoff at every milestone.
What about HubSpot certifications?+
Our engineering team holds HubSpot Solutions Architect, App Developer, and Platform Specialist certifications. Plus broader engineering credentials (AWS, GCP, TypeScript). We're not a generic agency stacking certifications, but we hold what's relevant to HubSpot deep work.
How do we get started?+
Book a 30-minute strategy call. We'll cover your use case, technical context, and the highest-leverage approach. Proposal within 48 hours if we're a fit.
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