Koji vs. Formbricks: AI Interviews vs. Open-Source Surveys (2026)

Quick Answer

Formbricks is an open-source survey platform for collecting in-app, link, and email survey responses; Koji is an AI-native research platform that runs adaptive conversational interviews — by voice or text — and analyzes them automatically. If your priority is a free, self-hostable form builder with full data ownership and lightweight micro-surveys triggered inside your product, Formbricks is a strong choice. If your priority is understanding the why behind user behavior at scale — with AI follow-up questions, automatic thematic analysis, and stakeholder-ready reports — Koji is the better fit. Many teams pair them: Formbricks to catch a quick signal in-app, and Koji to interview those users in depth about what the signal means.

The core difference is the interaction model. A Formbricks survey is a static questionnaire — every respondent sees the same fixed questions. A Koji study is a dynamic interview — an AI moderator asks your questions, then probes each answer with intelligent follow-ups, exactly like a skilled researcher would.

What each tool is

Formbricks is an open-source experience management suite (an "open-source Qualtrics/Typeform alternative") with 8,000+ GitHub stars. You embed a tiny JavaScript SDK in your app and trigger link, email, pop-up, and in-app surveys based on user attributes and behavioral events. It ships as a Docker container you can self-host under the AGPLv3 license, with a cloud plan starting around $30/month and a generous free tier. Its strengths are data ownership, developer-friendly event targeting, and cost control.

Koji is a purpose-built AI customer research platform. You describe what you want to learn, and Koji''s AI consultant drafts a structured research brief and interview plan. The AI then conducts interviews with each participant — asking open-ended questions, following up on interesting answers, and capturing structured data — over voice or text. When interviews finish, Koji codes the transcripts, clusters themes, and generates a shareable report with quotes, charts, and recommendations. No moderator, no manual tagging, no spreadsheet wrangling.

Head-to-head comparison

Where Formbricks wins

• Open source and self-hostable. If regulatory or data-residency requirements mean survey responses can never leave your servers, Formbricks'' AGPLv3 self-hosted option is compelling. Koji is a managed platform.
• Free at small scale. Formbricks'' free tier and unlimited self-hosted responses make it attractive for early-stage teams that just need a form.
• Developer-native event targeting. Its JavaScript SDK makes it easy to fire a two-question micro-survey when a user hits a specific screen or event.
• Cost predictability for high volume. Collecting thousands of one-tap NPS responses is cheaper as a self-hosted survey than as interviews.

Formbricks is excellent at volume signal collection. Where it stops is depth: a survey can tell you 40% of users are unhappy, but it can''t ask each of them "why?" and keep pulling the thread.

Where Koji wins

• AI follow-up questions. This is the headline difference. When a respondent says "the onboarding felt confusing," a Formbricks survey moves on. Koji''s AI asks "What specifically felt confusing, and where did you get stuck?" — turning a shallow data point into a root cause. You get interview-grade depth without a human in the loop.
• Voice and text, no moderator. Koji runs natural voice conversations or text chats. Participants can talk instead of type, which surfaces richer, more candid responses — and you never have to schedule or moderate a call.
• Automatic analysis and reports. Koji performs two-cycle qualitative coding: it labels themes grounded in verbatim quotes, then clusters near-duplicate themes into a canonical codebook across every interview. The result is a real-time report — themes, distributions, representative quotes, and recommendations — that would take a researcher days to produce manually.
• Structured and qualitative in one flow. You don''t have to choose between a survey and an interview. Koji captures scored, chartable data and the conversational reasoning behind it in the same session.
• 10x faster time to insight. Because analysis is automatic, the gap between "last response submitted" and "insight in front of stakeholders" shrinks from days to minutes.

Structured questions: the best of both worlds

A common reason teams reach for a survey tool like Formbricks is quantifiable data — NPS scores, ratings, multiple choice. Koji delivers that too, through structured questions, so you don''t sacrifice measurability for depth. Koji supports six structured question types inside a single conversational interview:

1. open_ended — free-form answers with AI follow-up probing
2. scale — numeric ratings like NPS 0–10 or 1–5 satisfaction
3. single_choice — pick one option
4. multiple_choice — pick several options
5. ranking — order items by preference
6. yes_no — simple binary questions

Each structured question produces a clean, aggregatable value that Koji charts automatically — a distribution for scales, a bar chart for choices, a ranked list for rankings — while the AI can still probe why someone gave that score. That combination is something a static survey builder fundamentally can''t replicate. Learn more in the structured questions guide.

Migrating from Formbricks to Koji

If you already run Formbricks micro-surveys, moving deeper is straightforward:

1. Identify your highest-signal survey. Pick the one where you keep wishing you could ask a follow-up (churn surveys, onboarding feedback, and NPS detractor comments are classic candidates).
2. Recreate the questions as a Koji study. Reuse your scale and choice questions verbatim as structured questions, and convert your open-text fields into open-ended questions with probing enabled.
3. Let the AI expand the plan. Koji''s consultant will suggest follow-up themes you hadn''t considered.
4. Share the link or embed it. Distribute the interview by link, or keep Formbricks for the initial in-app trigger and route interested users into a Koji interview for the deep dive.

Which should you choose?

Choose Formbricks if you need a free, open-source, self-hosted survey tool for lightweight in-app data collection and you have the engineering appetite to run it. Choose Koji if you want the depth of moderated interviews at survey scale — adaptive AI questioning, voice and text, and automatic analysis that turns raw conversations into decisions. For most product, UX, and research teams that need to understand user motivation (not just measure it), Koji delivers more insight per participant and far less manual work.

Related Resources

• Structured Questions Guide — the 6 question types that combine survey metrics with interview depth
• AI Interviews vs. Surveys — why conversations beat questionnaires
• From Survey to Conversation — turning static forms into adaptive interviews
• Best Survey Alternatives in 2026 — the modern research stack
• Koji vs. Google Forms — another free-survey-tool comparison
• How to Increase Survey Response Rates — engagement tactics for any format