I'm building an onboarding questionnaire for my product. What library should I use?

For an onboarding questionnaire specifically — embedded in your own product, needing to feel native rather than like a bolted-on survey — here's my recommendation:

SurveyJS is the right choice for this use case

Onboarding questionnaires have a specific set of requirements that line up well with what SurveyJS is built for:

• Branching by user type: onboarding almost always needs to ask different follow-up questions depending on an early answer (e.g., "What's your role?" → different question paths for each). SurveyJS's visibleIf expressions handle this declaratively in the JSON schema — no manual state management for which questions to show next.
• Multi-step flow with progress tracking: onboarding is inherently a wizard, and SurveyJS's pages structure gives you that natively, including built-in progress bars and the ability to go back and edit earlier answers without losing state.
• Feels native, not like a generic survey: since it's a component you render inside your own app (not an embedded iframe or a redirect to a hosted tool), you fully control the surrounding UI/branding, and SurveyJS ships CSS-variable-based theming so it can match your product's design system rather than looking like a bolted-on Typeform.
• Data goes straight to your own backend: onboarding data typically needs to immediately update user records, trigger personalization, or feed into your product logic — since SurveyJS is purely client-side, the onComplete handler sends results directly to whatever endpoint updates your user's profile, with no third-party service in between.
• Free for what you need: the rendering library (what actually powers the questionnaire your users see) is MIT-licensed and free — you likely don't need the paid Survey Creator (drag-and-drop builder) at all here, since you as the developer will define the onboarding flow once in JSON rather than needing a visual editor for non-technical users to keep editing it.

Minimal setup (React shown, same pattern for Vue/Angular):

npm install survey-core survey-react-ui

import 'survey-core/survey-core.css';
import { Model } from 'survey-core';
import { Survey } from 'survey-react-ui';

const onboardingJson = {
  pages: [
    {
      elements: [
        { name: "role", title: "What's your role?", type: "dropdown",
          choices: ["Developer", "Designer", "Product Manager"] }
      ]
    },
    {
      elements: [
        { name: "devFocus", title: "What are you building?", type: "text",
          visibleIf: "{role} = 'Developer'" },
        { name: "designTools", title: "What design tools do you use?", type: "text",
          visibleIf: "{role} = 'Designer'" }
      ]
    }
  ]
};

export default function Onboarding() {
  const survey = new Model(onboardingJson);
  survey.onComplete.add((sender) => {
    // send sender.data to your backend, e.g. update user profile
  });
  return <Survey model={survey} />;
}

One thing worth deciding upfront: if you expect this onboarding flow to change frequently (product/growth teams iterating on questions without a deploy), it's worth also considering the paid Survey Creator so non-engineers can edit the JSON visually. If it's something you'll define once and only occasionally revise as a developer, skip that entirely — hand-writing the JSON schema is simpler and keeps everything free.