For years I’ve been frustrated with how most online MBTI tests work.

A lot of the popular ones are essentially Big 5 questionnaires wearing MBTI labels but they measure dichotomy preferences, not cognitive mechanisms. That’s why they mistype anyone with nuance or a non-stereotypical cognitive stack.

Over the past decade I’ve manually typed more than 8,000 people through coaching calls, long-form questionnaires, and pattern audits. In the process I documented hundreds of distinctions that separate lookalike types (for example, Ni–Te vs. Ni–Fe, or why many INFJs consistently mistype as INFPs).

Eventually I realized I needed to stop keeping this logic in handwritten notes and build something scalable.



**What I Built**

**Function-First Engine**

It evaluates all eight cognitive functions directly (Ti, Te, Ni, Ne, etc.) rather than relying on EI/SN/TF/JP sliders.

**Adaptive Question Paths**

The test changes its question sequence based on your previous answers so it can dig into ambiguous areas.

**Borderline and Probability Modeling**

Instead of forcing a binary type, it shows probabilities, nearby alternative types, and the reasoning behind each.

**Full Transparency**

You will be able to see:

* which rules fired
* how function scores were calculated
* why the engine leaned toward one type over another
* what alternative pathways it considered Most tests today are essentially black boxes, and I wanted to fix that.



**Where Things Stand**

I’m finalizing the scoring engine now and preparing a closed beta for early 2026. I’m looking for:

* theorists who want to stress-test the logic
* skeptics who want to challenge assumptions
* enthusiasts who care about cognitive functions
* people who are consistently mistyped and can help refine edge cases



If you want to read the methodology or join the early access list, here’s the site:

[**tjpersonality.com**](http://tjpersonality.com)

I would appreciate any feedback on whether the methodology page accurately reflects the depth of the theory and whether anything feels unclear or incomplete.

Thanks for reading. Excited (and a bit nervous) to finally share this here.

After Typing 8,000+ People Over the Last Decade, I Finally Built a Function-First 1,000+ Rule MBTI Engine — Looking for Beta Testers