How do HubSpot forms work, and should you use HubSpot forms or your own?
HubSpot forms write straight to the CRM, which is usually worth the tradeoff.
A HubSpot form writes directly to the CRM, creates or updates the contact, and carries the visitor's session context with it. That is worth a lot, and it is why we default to HubSpot forms even on pages we built ourselves.
How they get onto a page
You can drop a form onto a HubSpot page in the editor, embed it on an external site with the embed code, or share it as a standalone page. HubSpot documents rendering the embed as raw HTML rather than inside an iframe, which is what you want when the form has to inherit your site styling, and lists that option with Marketing Hub or Content Hub Professional and Enterprise. Campaign association is documented with Marketing Hub Professional and Enterprise.
Progressive fields
Progressive fields let a form swap in a new question once a contact has already answered an earlier one, so a returning visitor is not asked for their first name again. This is the single highest value form feature most portals never turn on. Three fields that change on the second visit beat an eight field form that nobody completes.
When a custom form is the right call
Sometimes it is. Multi-step quoting tools, forms that have to validate against your own system before submitting, or a checkout flow where the form is part of an application rather than a marketing page. In those cases you post to the HubSpot Forms API instead. The thing to plan for: HubSpot's tracking code sets a visitor cookie, and the Forms API accepts that cookie value as context with the submission. If your custom form does not pass it, the record still gets created, but test what session and source context survives before you assume the analytics look the same.
What we do
Default to HubSpot forms. Keep them short. Use progressive fields instead of long forms. Keep field names consistent with your CRM properties so nothing needs mapping later. If a custom form is genuinely required, build it against the Forms API deliberately and test the attribution, rather than discovering the gap three months into a paid campaign.
Related: How do you track leads and conversions from paid campaigns?, Can LevelUp Digital build custom HubSpot integrations?, How to Generate More Inbound Leads, 10 UX Must-Haves for Your HubSpot Website.