If you are building AI agents and you have to pick one personality framework to put inside the identity file, do not pick MBTI. We say this knowing how popular MBTI is, how easy it is to socialise inside a team, and how many existing tools already use it. None of that is a good reason to put it at the load-bearing layer of an agent's soul.
What MBTI is actually good for
MBTI is excellent surface-level packaging. A user who sees "ENFJ-style assistant" forms a useful expectation in about half a second: warm, structured, future-oriented, comfortable leading. That's a real product win. The buyer doesn't need to study a 9-type system to feel oriented. MBTI's familiarity is a feature.
What it cannot do is tell you, or the agent, what to do when the situation goes off-script. "Be ENFJ-style" is not an executable instruction. Should the ENFJ-style agent escalate or de-escalate when the user is rude? Should it volunteer more information than asked? Should it refuse a task that conflicts with the user's stated goals? MBTI is silent on all of these. Those are the exact moments where trust is built or broken.
What the Enneagram does that MBTI cannot
- Specifies a default failure mode — what the agent does wrong, predictably.
- Specifies a stress trajectory — the disintegration arrow tells you exactly which other type's worst behaviour shows up under load.
- Specifies a growth trajectory — the integration arrow tells you what "this agent at its best" looks like, so you have a target.
- Specifies what the agent refuses, even when instructed to allow it.
How Ganjiang ships this
Every soul Ganjiang's Forge produces carries an Enneagram type, a wing, and an instinctual subtype in the soul.md file. Optionally, the same soul carries an MBTI-flavoured tone tag in the identity.md file — for the human users who will scan it and want a familiar handle. The MBTI line is for legibility. The Enneagram block is for behaviour. The agent's actual decisions trace back to the Enneagram every time.
“Put MBTI on the lanyard. Put the Enneagram in the operating manual. Treat the first as marketing and the second as engineering.”